Merge drm/drm-next into drm-intel-next

[linux-block.git] / drivers / gpu / drm / i915 / gt / intel_execlists_submission.c

// SPDX-License-Identifier: MIT
/*
 * Copyright © 2014 Intel Corporation
 */

/**
 * DOC: Logical Rings, Logical Ring Contexts and Execlists
 *
 * Motivation:
 * GEN8 brings an expansion of the HW contexts: "Logical Ring Contexts".
 * These expanded contexts enable a number of new abilities, especially
 * "Execlists" (also implemented in this file).
 *
 * One of the main differences with the legacy HW contexts is that logical
 * ring contexts incorporate many more things to the context's state, like
 * PDPs or ringbuffer control registers:
 *
 * The reason why PDPs are included in the context is straightforward: as
 * PPGTTs (per-process GTTs) are actually per-context, having the PDPs
 * contained there mean you don't need to do a ppgtt->switch_mm yourself,
 * instead, the GPU will do it for you on the context switch.
 *
 * But, what about the ringbuffer control registers (head, tail, etc..)?
 * shouldn't we just need a set of those per engine command streamer? This is
 * where the name "Logical Rings" starts to make sense: by virtualizing the
 * rings, the engine cs shifts to a new "ring buffer" with every context
 * switch. When you want to submit a workload to the GPU you: A) choose your
 * context, B) find its appropriate virtualized ring, C) write commands to it
 * and then, finally, D) tell the GPU to switch to that context.
 *
 * Instead of the legacy MI_SET_CONTEXT, the way you tell the GPU to switch
 * to a contexts is via a context execution list, ergo "Execlists".
 *
 * LRC implementation:
 * Regarding the creation of contexts, we have:
 *
 * - One global default context.
 * - One local default context for each opened fd.
 * - One local extra context for each context create ioctl call.
 *
 * Now that ringbuffers belong per-context (and not per-engine, like before)
 * and that contexts are uniquely tied to a given engine (and not reusable,
 * like before) we need:
 *
 * - One ringbuffer per-engine inside each context.
 * - One backing object per-engine inside each context.
 *
 * The global default context starts its life with these new objects fully
 * allocated and populated. The local default context for each opened fd is
 * more complex, because we don't know at creation time which engine is going
 * to use them. To handle this, we have implemented a deferred creation of LR
 * contexts:
 *
 * The local context starts its life as a hollow or blank holder, that only
 * gets populated for a given engine once we receive an execbuffer. If later
 * on we receive another execbuffer ioctl for the same context but a different
 * engine, we allocate/populate a new ringbuffer and context backing object and
 * so on.
 *
 * Finally, regarding local contexts created using the ioctl call: as they are
 * only allowed with the render ring, we can allocate & populate them right
 * away (no need to defer anything, at least for now).
 *
 * Execlists implementation:
 * Execlists are the new method by which, on gen8+ hardware, workloads are
 * submitted for execution (as opposed to the legacy, ringbuffer-based, method).
 * This method works as follows:
 *
 * When a request is committed, its commands (the BB start and any leading or
 * trailing commands, like the seqno breadcrumbs) are placed in the ringbuffer
 * for the appropriate context. The tail pointer in the hardware context is not
 * updated at this time, but instead, kept by the driver in the ringbuffer
 * structure. A structure representing this request is added to a request queue
 * for the appropriate engine: this structure contains a copy of the context's
 * tail after the request was written to the ring buffer and a pointer to the
 * context itself.
 *
 * If the engine's request queue was empty before the request was added, the
 * queue is processed immediately. Otherwise the queue will be processed during
 * a context switch interrupt. In any case, elements on the queue will get sent
 * (in pairs) to the GPU's ExecLists Submit Port (ELSP, for short) with a
 * globally unique 20-bits submission ID.
 *
 * When execution of a request completes, the GPU updates the context status
 * buffer with a context complete event and generates a context switch interrupt.
 * During the interrupt handling, the driver examines the events in the buffer:
 * for each context complete event, if the announced ID matches that on the head
 * of the request queue, then that request is retired and removed from the queue.
 *
 * After processing, if any requests were retired and the queue is not empty
 * then a new execution list can be submitted. The two requests at the front of
 * the queue are next to be submitted but since a context may not occur twice in
 * an execution list, if subsequent requests have the same ID as the first then
 * the two requests must be combined. This is done simply by discarding requests
 * at the head of the queue until either only one requests is left (in which case
 * we use a NULL second context) or the first two requests have unique IDs.
 *
 * By always executing the first two requests in the queue the driver ensures
 * that the GPU is kept as busy as possible. In the case where a single context
 * completes but a second context is still executing, the request for this second
 * context will be at the head of the queue when we remove the first one. This
 * request will then be resubmitted along with a new request for a different context,
 * which will cause the hardware to continue executing the second request and queue
 * the new request (the GPU detects the condition of a context getting preempted
 * with the same context and optimizes the context switch flow by not doing
 * preemption, but just sampling the new tail pointer).
 *
 */
#include <linux/interrupt.h>
#include <linux/string_helpers.h>

#include "i915_drv.h"
#include "i915_trace.h"
#include "i915_vgpu.h"
#include "gen8_engine_cs.h"
#include "intel_breadcrumbs.h"
#include "intel_context.h"
#include "intel_engine_heartbeat.h"
#include "intel_engine_pm.h"
#include "intel_engine_regs.h"
#include "intel_engine_stats.h"
#include "intel_execlists_submission.h"
#include "intel_gt.h"
#include "intel_gt_irq.h"
#include "intel_gt_pm.h"
#include "intel_gt_regs.h"
#include "intel_gt_requests.h"
#include "intel_lrc.h"
#include "intel_lrc_reg.h"
#include "intel_mocs.h"
#include "intel_reset.h"
#include "intel_ring.h"
#include "intel_workarounds.h"
#include "shmem_utils.h"

#define RING_EXECLIST_QFULL             (1 << 0x2)
#define RING_EXECLIST1_VALID            (1 << 0x3)
#define RING_EXECLIST0_VALID            (1 << 0x4)
#define RING_EXECLIST_ACTIVE_STATUS     (3 << 0xE)
#define RING_EXECLIST1_ACTIVE           (1 << 0x11)
#define RING_EXECLIST0_ACTIVE           (1 << 0x12)

#define GEN8_CTX_STATUS_IDLE_ACTIVE     (1 << 0)
#define GEN8_CTX_STATUS_PREEMPTED       (1 << 1)
#define GEN8_CTX_STATUS_ELEMENT_SWITCH  (1 << 2)
#define GEN8_CTX_STATUS_ACTIVE_IDLE     (1 << 3)
#define GEN8_CTX_STATUS_COMPLETE        (1 << 4)
#define GEN8_CTX_STATUS_LITE_RESTORE    (1 << 15)

#define GEN8_CTX_STATUS_COMPLETED_MASK \
         (GEN8_CTX_STATUS_COMPLETE | GEN8_CTX_STATUS_PREEMPTED)

#define GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE  (0x1) /* lower csb dword */
#define GEN12_CTX_SWITCH_DETAIL(csb_dw) ((csb_dw) & 0xF) /* upper csb dword */
#define GEN12_CSB_SW_CTX_ID_MASK                GENMASK(25, 15)
#define GEN12_IDLE_CTX_ID               0x7FF
#define GEN12_CSB_CTX_VALID(csb_dw) \
        (FIELD_GET(GEN12_CSB_SW_CTX_ID_MASK, csb_dw) != GEN12_IDLE_CTX_ID)

#define XEHP_CTX_STATUS_SWITCHED_TO_NEW_QUEUE   BIT(1) /* upper csb dword */
#define XEHP_CSB_SW_CTX_ID_MASK                 GENMASK(31, 10)
#define XEHP_IDLE_CTX_ID                        0xFFFF
#define XEHP_CSB_CTX_VALID(csb_dw) \
        (FIELD_GET(XEHP_CSB_SW_CTX_ID_MASK, csb_dw) != XEHP_IDLE_CTX_ID)

/* Typical size of the average request (2 pipecontrols and a MI_BB) */
#define EXECLISTS_REQUEST_SIZE 64 /* bytes */

struct virtual_engine {
        struct intel_engine_cs base;
        struct intel_context context;
        struct rcu_work rcu;

        /*
         * We allow only a single request through the virtual engine at a time
         * (each request in the timeline waits for the completion fence of
         * the previous before being submitted). By restricting ourselves to
         * only submitting a single request, each request is placed on to a
         * physical to maximise load spreading (by virtue of the late greedy
         * scheduling -- each real engine takes the next available request
         * upon idling).
         */
        struct i915_request *request;

        /*
         * We keep a rbtree of available virtual engines inside each physical
         * engine, sorted by priority. Here we preallocate the nodes we need
         * for the virtual engine, indexed by physical_engine->id.
         */
        struct ve_node {
                struct rb_node rb;
                int prio;
        } nodes[I915_NUM_ENGINES];

        /* And finally, which physical engines this virtual engine maps onto. */
        unsigned int num_siblings;
        struct intel_engine_cs *siblings[];
};

static struct virtual_engine *to_virtual_engine(struct intel_engine_cs *engine)
{
        GEM_BUG_ON(!intel_engine_is_virtual(engine));
        return container_of(engine, struct virtual_engine, base);
}

static struct intel_context *
execlists_create_virtual(struct intel_engine_cs **siblings, unsigned int count,
                         unsigned long flags);

static struct i915_request *
__active_request(const struct intel_timeline * const tl,
                 struct i915_request *rq,
                 int error)
{
        struct i915_request *active = rq;

        list_for_each_entry_from_reverse(rq, &tl->requests, link) {
                if (__i915_request_is_complete(rq))
                        break;

                if (error) {
                        i915_request_set_error_once(rq, error);
                        __i915_request_skip(rq);
                }
                active = rq;
        }

        return active;
}

static struct i915_request *
active_request(const struct intel_timeline * const tl, struct i915_request *rq)
{
        return __active_request(tl, rq, 0);
}

static void ring_set_paused(const struct intel_engine_cs *engine, int state)
{
        /*
         * We inspect HWS_PREEMPT with a semaphore inside
         * engine->emit_fini_breadcrumb. If the dword is true,
         * the ring is paused as the semaphore will busywait
         * until the dword is false.
         */
        engine->status_page.addr[I915_GEM_HWS_PREEMPT] = state;
        if (state)
                wmb();
}

static struct i915_priolist *to_priolist(struct rb_node *rb)
{
        return rb_entry(rb, struct i915_priolist, node);
}

static int rq_prio(const struct i915_request *rq)
{
        return READ_ONCE(rq->sched.attr.priority);
}

static int effective_prio(const struct i915_request *rq)
{
        int prio = rq_prio(rq);

        /*
         * If this request is special and must not be interrupted at any
         * cost, so be it. Note we are only checking the most recent request
         * in the context and so may be masking an earlier vip request. It
         * is hoped that under the conditions where nopreempt is used, this
         * will not matter (i.e. all requests to that context will be
         * nopreempt for as long as desired).
         */
        if (i915_request_has_nopreempt(rq))
                prio = I915_PRIORITY_UNPREEMPTABLE;

        return prio;
}

static int queue_prio(const struct i915_sched_engine *sched_engine)
{
        struct rb_node *rb;

        rb = rb_first_cached(&sched_engine->queue);
        if (!rb)
                return INT_MIN;

        return to_priolist(rb)->priority;
}

static int virtual_prio(const struct intel_engine_execlists *el)
{
        struct rb_node *rb = rb_first_cached(&el->virtual);

        return rb ? rb_entry(rb, struct ve_node, rb)->prio : INT_MIN;
}

static bool need_preempt(const struct intel_engine_cs *engine,
                         const struct i915_request *rq)
{
        int last_prio;

        if (!intel_engine_has_semaphores(engine))
                return false;

        /*
         * Check if the current priority hint merits a preemption attempt.
         *
         * We record the highest value priority we saw during rescheduling
         * prior to this dequeue, therefore we know that if it is strictly
         * less than the current tail of ESLP[0], we do not need to force
         * a preempt-to-idle cycle.
         *
         * However, the priority hint is a mere hint that we may need to
         * preempt. If that hint is stale or we may be trying to preempt
         * ourselves, ignore the request.
         *
         * More naturally we would write
         *      prio >= max(0, last);
         * except that we wish to prevent triggering preemption at the same
         * priority level: the task that is running should remain running
         * to preserve FIFO ordering of dependencies.
         */
        last_prio = max(effective_prio(rq), I915_PRIORITY_NORMAL - 1);
        if (engine->sched_engine->queue_priority_hint <= last_prio)
                return false;

        /*
         * Check against the first request in ELSP[1], it will, thanks to the
         * power of PI, be the highest priority of that context.
         */
        if (!list_is_last(&rq->sched.link, &engine->sched_engine->requests) &&
            rq_prio(list_next_entry(rq, sched.link)) > last_prio)
                return true;

        /*
         * If the inflight context did not trigger the preemption, then maybe
         * it was the set of queued requests? Pick the highest priority in
         * the queue (the first active priolist) and see if it deserves to be
         * running instead of ELSP[0].
         *
         * The highest priority request in the queue can not be either
         * ELSP[0] or ELSP[1] as, thanks again to PI, if it was the same
         * context, it's priority would not exceed ELSP[0] aka last_prio.
         */
        return max(virtual_prio(&engine->execlists),
                   queue_prio(engine->sched_engine)) > last_prio;
}

__maybe_unused static bool
assert_priority_queue(const struct i915_request *prev,
                      const struct i915_request *next)
{
        /*
         * Without preemption, the prev may refer to the still active element
         * which we refuse to let go.
         *
         * Even with preemption, there are times when we think it is better not
         * to preempt and leave an ostensibly lower priority request in flight.
         */
        if (i915_request_is_active(prev))
                return true;

        return rq_prio(prev) >= rq_prio(next);
}

static struct i915_request *
__unwind_incomplete_requests(struct intel_engine_cs *engine)
{
        struct i915_request *rq, *rn, *active = NULL;
        struct list_head *pl;
        int prio = I915_PRIORITY_INVALID;

        lockdep_assert_held(&engine->sched_engine->lock);

        list_for_each_entry_safe_reverse(rq, rn,
                                         &engine->sched_engine->requests,
                                         sched.link) {
                if (__i915_request_is_complete(rq)) {
                        list_del_init(&rq->sched.link);
                        continue;
                }

                __i915_request_unsubmit(rq);

                GEM_BUG_ON(rq_prio(rq) == I915_PRIORITY_INVALID);
                if (rq_prio(rq) != prio) {
                        prio = rq_prio(rq);
                        pl = i915_sched_lookup_priolist(engine->sched_engine,
                                                        prio);
                }
                GEM_BUG_ON(i915_sched_engine_is_empty(engine->sched_engine));

                list_move(&rq->sched.link, pl);
                set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);

                /* Check in case we rollback so far we wrap [size/2] */
                if (intel_ring_direction(rq->ring,
                                         rq->tail,
                                         rq->ring->tail + 8) > 0)
                        rq->context->lrc.desc |= CTX_DESC_FORCE_RESTORE;

                active = rq;
        }

        return active;
}

struct i915_request *
execlists_unwind_incomplete_requests(struct intel_engine_execlists *execlists)
{
        struct intel_engine_cs *engine =
                container_of(execlists, typeof(*engine), execlists);

        return __unwind_incomplete_requests(engine);
}

static void
execlists_context_status_change(struct i915_request *rq, unsigned long status)
{
        /*
         * Only used when GVT-g is enabled now. When GVT-g is disabled,
         * The compiler should eliminate this function as dead-code.
         */
        if (!IS_ENABLED(CONFIG_DRM_I915_GVT))
                return;

        atomic_notifier_call_chain(&rq->engine->context_status_notifier,
                                   status, rq);
}

static void reset_active(struct i915_request *rq,
                         struct intel_engine_cs *engine)
{
        struct intel_context * const ce = rq->context;
        u32 head;

        /*
         * The executing context has been cancelled. We want to prevent
         * further execution along this context and propagate the error on
         * to anything depending on its results.
         *
         * In __i915_request_submit(), we apply the -EIO and remove the
         * requests' payloads for any banned requests. But first, we must
         * rewind the context back to the start of the incomplete request so
         * that we do not jump back into the middle of the batch.
         *
         * We preserve the breadcrumbs and semaphores of the incomplete
         * requests so that inter-timeline dependencies (i.e other timelines)
         * remain correctly ordered. And we defer to __i915_request_submit()
         * so that all asynchronous waits are correctly handled.
         */
        ENGINE_TRACE(engine, "{ reset rq=%llx:%lld }\n",
                     rq->fence.context, rq->fence.seqno);

        /* On resubmission of the active request, payload will be scrubbed */
        if (__i915_request_is_complete(rq))
                head = rq->tail;
        else
                head = __active_request(ce->timeline, rq, -EIO)->head;
        head = intel_ring_wrap(ce->ring, head);

        /* Scrub the context image to prevent replaying the previous batch */
        lrc_init_regs(ce, engine, true);

        /* We've switched away, so this should be a no-op, but intent matters */
        ce->lrc.lrca = lrc_update_regs(ce, engine, head);
}

static bool bad_request(const struct i915_request *rq)
{
        return rq->fence.error && i915_request_started(rq);
}

static struct intel_engine_cs *
__execlists_schedule_in(struct i915_request *rq)
{
        struct intel_engine_cs * const engine = rq->engine;
        struct intel_context * const ce = rq->context;

        intel_context_get(ce);

        if (unlikely(intel_context_is_closed(ce) &&
                     !intel_engine_has_heartbeat(engine)))
                intel_context_set_banned(ce);

        if (unlikely(intel_context_is_banned(ce) || bad_request(rq)))
                reset_active(rq, engine);

        if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
                lrc_check_regs(ce, engine, "before");

        if (ce->tag) {
                /* Use a fixed tag for OA and friends */
                GEM_BUG_ON(ce->tag <= BITS_PER_LONG);
                ce->lrc.ccid = ce->tag;
        } else if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50)) {
                /* We don't need a strict matching tag, just different values */
                unsigned int tag = ffs(READ_ONCE(engine->context_tag));

                GEM_BUG_ON(tag == 0 || tag >= BITS_PER_LONG);
                clear_bit(tag - 1, &engine->context_tag);
                ce->lrc.ccid = tag << (XEHP_SW_CTX_ID_SHIFT - 32);

                BUILD_BUG_ON(BITS_PER_LONG > GEN12_MAX_CONTEXT_HW_ID);

        } else {
                /* We don't need a strict matching tag, just different values */
                unsigned int tag = __ffs(engine->context_tag);

                GEM_BUG_ON(tag >= BITS_PER_LONG);
                __clear_bit(tag, &engine->context_tag);
                ce->lrc.ccid = (1 + tag) << (GEN11_SW_CTX_ID_SHIFT - 32);

                BUILD_BUG_ON(BITS_PER_LONG > GEN12_MAX_CONTEXT_HW_ID);
        }

        ce->lrc.ccid |= engine->execlists.ccid;

        __intel_gt_pm_get(engine->gt);
        if (engine->fw_domain && !engine->fw_active++)
                intel_uncore_forcewake_get(engine->uncore, engine->fw_domain);
        execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_IN);
        intel_engine_context_in(engine);

        CE_TRACE(ce, "schedule-in, ccid:%x\n", ce->lrc.ccid);

        return engine;
}

static void execlists_schedule_in(struct i915_request *rq, int idx)
{
        struct intel_context * const ce = rq->context;
        struct intel_engine_cs *old;

        GEM_BUG_ON(!intel_engine_pm_is_awake(rq->engine));
        trace_i915_request_in(rq, idx);

        old = ce->inflight;
        if (!old)
                old = __execlists_schedule_in(rq);
        WRITE_ONCE(ce->inflight, ptr_inc(old));

        GEM_BUG_ON(intel_context_inflight(ce) != rq->engine);
}

static void
resubmit_virtual_request(struct i915_request *rq, struct virtual_engine *ve)
{
        struct intel_engine_cs *engine = rq->engine;

        spin_lock_irq(&engine->sched_engine->lock);

        clear_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
        WRITE_ONCE(rq->engine, &ve->base);
        ve->base.submit_request(rq);

        spin_unlock_irq(&engine->sched_engine->lock);
}

static void kick_siblings(struct i915_request *rq, struct intel_context *ce)
{
        struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
        struct intel_engine_cs *engine = rq->engine;

        /*
         * After this point, the rq may be transferred to a new sibling, so
         * before we clear ce->inflight make sure that the context has been
         * removed from the b->signalers and furthermore we need to make sure
         * that the concurrent iterator in signal_irq_work is no longer
         * following ce->signal_link.
         */
        if (!list_empty(&ce->signals))
                intel_context_remove_breadcrumbs(ce, engine->breadcrumbs);

        /*
         * This engine is now too busy to run this virtual request, so
         * see if we can find an alternative engine for it to execute on.
         * Once a request has become bonded to this engine, we treat it the
         * same as other native request.
         */
        if (i915_request_in_priority_queue(rq) &&
            rq->execution_mask != engine->mask)
                resubmit_virtual_request(rq, ve);

        if (READ_ONCE(ve->request))
                tasklet_hi_schedule(&ve->base.sched_engine->tasklet);
}

static void __execlists_schedule_out(struct i915_request * const rq,
                                     struct intel_context * const ce)
{
        struct intel_engine_cs * const engine = rq->engine;
        unsigned int ccid;

        /*
         * NB process_csb() is not under the engine->sched_engine->lock and hence
         * schedule_out can race with schedule_in meaning that we should
         * refrain from doing non-trivial work here.
         */

        CE_TRACE(ce, "schedule-out, ccid:%x\n", ce->lrc.ccid);
        GEM_BUG_ON(ce->inflight != engine);

        if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
                lrc_check_regs(ce, engine, "after");

        /*
         * If we have just completed this context, the engine may now be
         * idle and we want to re-enter powersaving.
         */
        if (intel_timeline_is_last(ce->timeline, rq) &&
            __i915_request_is_complete(rq))
                intel_engine_add_retire(engine, ce->timeline);

        ccid = ce->lrc.ccid;
        if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50)) {
                ccid >>= XEHP_SW_CTX_ID_SHIFT - 32;
                ccid &= XEHP_MAX_CONTEXT_HW_ID;
        } else {
                ccid >>= GEN11_SW_CTX_ID_SHIFT - 32;
                ccid &= GEN12_MAX_CONTEXT_HW_ID;
        }

        if (ccid < BITS_PER_LONG) {
                GEM_BUG_ON(ccid == 0);
                GEM_BUG_ON(test_bit(ccid - 1, &engine->context_tag));
                __set_bit(ccid - 1, &engine->context_tag);
        }

        lrc_update_runtime(ce);
        intel_engine_context_out(engine);
        execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
        if (engine->fw_domain && !--engine->fw_active)
                intel_uncore_forcewake_put(engine->uncore, engine->fw_domain);
        intel_gt_pm_put_async(engine->gt);

        /*
         * If this is part of a virtual engine, its next request may
         * have been blocked waiting for access to the active context.
         * We have to kick all the siblings again in case we need to
         * switch (e.g. the next request is not runnable on this
         * engine). Hopefully, we will already have submitted the next
         * request before the tasklet runs and do not need to rebuild
         * each virtual tree and kick everyone again.
         */
        if (ce->engine != engine)
                kick_siblings(rq, ce);

        WRITE_ONCE(ce->inflight, NULL);
        intel_context_put(ce);
}

static inline void execlists_schedule_out(struct i915_request *rq)
{
        struct intel_context * const ce = rq->context;

        trace_i915_request_out(rq);

        GEM_BUG_ON(!ce->inflight);
        ce->inflight = ptr_dec(ce->inflight);
        if (!__intel_context_inflight_count(ce->inflight))
                __execlists_schedule_out(rq, ce);

        i915_request_put(rq);
}

static u64 execlists_update_context(struct i915_request *rq)
{
        struct intel_context *ce = rq->context;
        u64 desc;
        u32 tail, prev;

        desc = ce->lrc.desc;
        if (rq->engine->flags & I915_ENGINE_HAS_EU_PRIORITY)
                desc |= lrc_desc_priority(rq_prio(rq));

        /*
         * WaIdleLiteRestore:bdw,skl
         *
         * We should never submit the context with the same RING_TAIL twice
         * just in case we submit an empty ring, which confuses the HW.
         *
         * We append a couple of NOOPs (gen8_emit_wa_tail) after the end of
         * the normal request to be able to always advance the RING_TAIL on
         * subsequent resubmissions (for lite restore). Should that fail us,
         * and we try and submit the same tail again, force the context
         * reload.
         *
         * If we need to return to a preempted context, we need to skip the
         * lite-restore and force it to reload the RING_TAIL. Otherwise, the
         * HW has a tendency to ignore us rewinding the TAIL to the end of
         * an earlier request.
         */
        GEM_BUG_ON(ce->lrc_reg_state[CTX_RING_TAIL] != rq->ring->tail);
        prev = rq->ring->tail;
        tail = intel_ring_set_tail(rq->ring, rq->tail);
        if (unlikely(intel_ring_direction(rq->ring, tail, prev) <= 0))
                desc |= CTX_DESC_FORCE_RESTORE;
        ce->lrc_reg_state[CTX_RING_TAIL] = tail;
        rq->tail = rq->wa_tail;

        /*
         * Make sure the context image is complete before we submit it to HW.
         *
         * Ostensibly, writes (including the WCB) should be flushed prior to
         * an uncached write such as our mmio register access, the empirical
         * evidence (esp. on Braswell) suggests that the WC write into memory
         * may not be visible to the HW prior to the completion of the UC
         * register write and that we may begin execution from the context
         * before its image is complete leading to invalid PD chasing.
         */
        wmb();

        ce->lrc.desc &= ~CTX_DESC_FORCE_RESTORE;
        return desc;
}

static void write_desc(struct intel_engine_execlists *execlists, u64 desc, u32 port)
{
        if (execlists->ctrl_reg) {
                writel(lower_32_bits(desc), execlists->submit_reg + port * 2);
                writel(upper_32_bits(desc), execlists->submit_reg + port * 2 + 1);
        } else {
                writel(upper_32_bits(desc), execlists->submit_reg);
                writel(lower_32_bits(desc), execlists->submit_reg);
        }
}

static __maybe_unused char *
dump_port(char *buf, int buflen, const char *prefix, struct i915_request *rq)
{
        if (!rq)
                return "";

        snprintf(buf, buflen, "%sccid:%x %llx:%lld%s prio %d",
                 prefix,
                 rq->context->lrc.ccid,
                 rq->fence.context, rq->fence.seqno,
                 __i915_request_is_complete(rq) ? "!" :
                 __i915_request_has_started(rq) ? "*" :
                 "",
                 rq_prio(rq));

        return buf;
}

static __maybe_unused noinline void
trace_ports(const struct intel_engine_execlists *execlists,
            const char *msg,
            struct i915_request * const *ports)
{
        const struct intel_engine_cs *engine =
                container_of(execlists, typeof(*engine), execlists);
        char __maybe_unused p0[40], p1[40];

        if (!ports[0])
                return;

        ENGINE_TRACE(engine, "%s { %s%s }\n", msg,
                     dump_port(p0, sizeof(p0), "", ports[0]),
                     dump_port(p1, sizeof(p1), ", ", ports[1]));
}

static bool
reset_in_progress(const struct intel_engine_cs *engine)
{
        return unlikely(!__tasklet_is_enabled(&engine->sched_engine->tasklet));
}

static __maybe_unused noinline bool
assert_pending_valid(const struct intel_engine_execlists *execlists,
                     const char *msg)
{
        struct intel_engine_cs *engine =
                container_of(execlists, typeof(*engine), execlists);
        struct i915_request * const *port, *rq, *prev = NULL;
        struct intel_context *ce = NULL;
        u32 ccid = -1;

        trace_ports(execlists, msg, execlists->pending);

        /* We may be messing around with the lists during reset, lalala */
        if (reset_in_progress(engine))
                return true;

        if (!execlists->pending[0]) {
                GEM_TRACE_ERR("%s: Nothing pending for promotion!\n",
                              engine->name);
                return false;
        }

        if (execlists->pending[execlists_num_ports(execlists)]) {
                GEM_TRACE_ERR("%s: Excess pending[%d] for promotion!\n",
                              engine->name, execlists_num_ports(execlists));
                return false;
        }

        for (port = execlists->pending; (rq = *port); port++) {
                unsigned long flags;
                bool ok = true;

                GEM_BUG_ON(!kref_read(&rq->fence.refcount));
                GEM_BUG_ON(!i915_request_is_active(rq));

                if (ce == rq->context) {
                        GEM_TRACE_ERR("%s: Dup context:%llx in pending[%zd]\n",
                                      engine->name,
                                      ce->timeline->fence_context,
                                      port - execlists->pending);
                        return false;
                }
                ce = rq->context;

                if (ccid == ce->lrc.ccid) {
                        GEM_TRACE_ERR("%s: Dup ccid:%x context:%llx in pending[%zd]\n",
                                      engine->name,
                                      ccid, ce->timeline->fence_context,
                                      port - execlists->pending);
                        return false;
                }
                ccid = ce->lrc.ccid;

                /*
                 * Sentinels are supposed to be the last request so they flush
                 * the current execution off the HW. Check that they are the only
                 * request in the pending submission.
                 *
                 * NB: Due to the async nature of preempt-to-busy and request
                 * cancellation we need to handle the case where request
                 * becomes a sentinel in parallel to CSB processing.
                 */
                if (prev && i915_request_has_sentinel(prev) &&
                    !READ_ONCE(prev->fence.error)) {
                        GEM_TRACE_ERR("%s: context:%llx after sentinel in pending[%zd]\n",
                                      engine->name,
                                      ce->timeline->fence_context,
                                      port - execlists->pending);
                        return false;
                }
                prev = rq;

                /*
                 * We want virtual requests to only be in the first slot so
                 * that they are never stuck behind a hog and can be immediately
                 * transferred onto the next idle engine.
                 */
                if (rq->execution_mask != engine->mask &&
                    port != execlists->pending) {
                        GEM_TRACE_ERR("%s: virtual engine:%llx not in prime position[%zd]\n",
                                      engine->name,
                                      ce->timeline->fence_context,
                                      port - execlists->pending);
                        return false;
                }

                /* Hold tightly onto the lock to prevent concurrent retires! */
                if (!spin_trylock_irqsave(&rq->lock, flags))
                        continue;

                if (__i915_request_is_complete(rq))
                        goto unlock;

                if (i915_active_is_idle(&ce->active) &&
                    !intel_context_is_barrier(ce)) {
                        GEM_TRACE_ERR("%s: Inactive context:%llx in pending[%zd]\n",
                                      engine->name,
                                      ce->timeline->fence_context,
                                      port - execlists->pending);
                        ok = false;
                        goto unlock;
                }

                if (!i915_vma_is_pinned(ce->state)) {
                        GEM_TRACE_ERR("%s: Unpinned context:%llx in pending[%zd]\n",
                                      engine->name,
                                      ce->timeline->fence_context,
                                      port - execlists->pending);
                        ok = false;
                        goto unlock;
                }

                if (!i915_vma_is_pinned(ce->ring->vma)) {
                        GEM_TRACE_ERR("%s: Unpinned ring:%llx in pending[%zd]\n",
                                      engine->name,
                                      ce->timeline->fence_context,
                                      port - execlists->pending);
                        ok = false;
                        goto unlock;
                }

unlock:
                spin_unlock_irqrestore(&rq->lock, flags);
                if (!ok)
                        return false;
        }

        return ce;
}

static void execlists_submit_ports(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists *execlists = &engine->execlists;
        unsigned int n;

        GEM_BUG_ON(!assert_pending_valid(execlists, "submit"));

        /*
         * We can skip acquiring intel_runtime_pm_get() here as it was taken
         * on our behalf by the request (see i915_gem_mark_busy()) and it will
         * not be relinquished until the device is idle (see
         * i915_gem_idle_work_handler()). As a precaution, we make sure
         * that all ELSP are drained i.e. we have processed the CSB,
         * before allowing ourselves to idle and calling intel_runtime_pm_put().
         */
        GEM_BUG_ON(!intel_engine_pm_is_awake(engine));

        /*
         * ELSQ note: the submit queue is not cleared after being submitted
         * to the HW so we need to make sure we always clean it up. This is
         * currently ensured by the fact that we always write the same number
         * of elsq entries, keep this in mind before changing the loop below.
         */
        for (n = execlists_num_ports(execlists); n--; ) {
                struct i915_request *rq = execlists->pending[n];

                write_desc(execlists,
                           rq ? execlists_update_context(rq) : 0,
                           n);
        }

        /* we need to manually load the submit queue */
        if (execlists->ctrl_reg)
                writel(EL_CTRL_LOAD, execlists->ctrl_reg);
}

static bool ctx_single_port_submission(const struct intel_context *ce)
{
        return (IS_ENABLED(CONFIG_DRM_I915_GVT) &&
                intel_context_force_single_submission(ce));
}

static bool can_merge_ctx(const struct intel_context *prev,
                          const struct intel_context *next)
{
        if (prev != next)
                return false;

        if (ctx_single_port_submission(prev))
                return false;

        return true;
}

static unsigned long i915_request_flags(const struct i915_request *rq)
{
        return READ_ONCE(rq->fence.flags);
}

static bool can_merge_rq(const struct i915_request *prev,
                         const struct i915_request *next)
{
        GEM_BUG_ON(prev == next);
        GEM_BUG_ON(!assert_priority_queue(prev, next));

        /*
         * We do not submit known completed requests. Therefore if the next
         * request is already completed, we can pretend to merge it in
         * with the previous context (and we will skip updating the ELSP
         * and tracking). Thus hopefully keeping the ELSP full with active
         * contexts, despite the best efforts of preempt-to-busy to confuse
         * us.
         */
        if (__i915_request_is_complete(next))
                return true;

        if (unlikely((i915_request_flags(prev) | i915_request_flags(next)) &
                     (BIT(I915_FENCE_FLAG_NOPREEMPT) |
                      BIT(I915_FENCE_FLAG_SENTINEL))))
                return false;

        if (!can_merge_ctx(prev->context, next->context))
                return false;

        GEM_BUG_ON(i915_seqno_passed(prev->fence.seqno, next->fence.seqno));
        return true;
}

static bool virtual_matches(const struct virtual_engine *ve,
                            const struct i915_request *rq,
                            const struct intel_engine_cs *engine)
{
        const struct intel_engine_cs *inflight;

        if (!rq)
                return false;

        if (!(rq->execution_mask & engine->mask)) /* We peeked too soon! */
                return false;

        /*
         * We track when the HW has completed saving the context image
         * (i.e. when we have seen the final CS event switching out of
         * the context) and must not overwrite the context image before
         * then. This restricts us to only using the active engine
         * while the previous virtualized request is inflight (so
         * we reuse the register offsets). This is a very small
         * hystersis on the greedy seelction algorithm.
         */
        inflight = intel_context_inflight(&ve->context);
        if (inflight && inflight != engine)
                return false;

        return true;
}

static struct virtual_engine *
first_virtual_engine(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists *el = &engine->execlists;
        struct rb_node *rb = rb_first_cached(&el->virtual);

        while (rb) {
                struct virtual_engine *ve =
                        rb_entry(rb, typeof(*ve), nodes[engine->id].rb);
                struct i915_request *rq = READ_ONCE(ve->request);

                /* lazily cleanup after another engine handled rq */
                if (!rq || !virtual_matches(ve, rq, engine)) {
                        rb_erase_cached(rb, &el->virtual);
                        RB_CLEAR_NODE(rb);
                        rb = rb_first_cached(&el->virtual);
                        continue;
                }

                return ve;
        }

        return NULL;
}

static void virtual_xfer_context(struct virtual_engine *ve,
                                 struct intel_engine_cs *engine)
{
        unsigned int n;

        if (likely(engine == ve->siblings[0]))
                return;

        GEM_BUG_ON(READ_ONCE(ve->context.inflight));
        if (!intel_engine_has_relative_mmio(engine))
                lrc_update_offsets(&ve->context, engine);

        /*
         * Move the bound engine to the top of the list for
         * future execution. We then kick this tasklet first
         * before checking others, so that we preferentially
         * reuse this set of bound registers.
         */
        for (n = 1; n < ve->num_siblings; n++) {
                if (ve->siblings[n] == engine) {
                        swap(ve->siblings[n], ve->siblings[0]);
                        break;
                }
        }
}

static void defer_request(struct i915_request *rq, struct list_head * const pl)
{
        LIST_HEAD(list);

        /*
         * We want to move the interrupted request to the back of
         * the round-robin list (i.e. its priority level), but
         * in doing so, we must then move all requests that were in
         * flight and were waiting for the interrupted request to
         * be run after it again.
         */
        do {
                struct i915_dependency *p;

                GEM_BUG_ON(i915_request_is_active(rq));
                list_move_tail(&rq->sched.link, pl);

                for_each_waiter(p, rq) {
                        struct i915_request *w =
                                container_of(p->waiter, typeof(*w), sched);

                        if (p->flags & I915_DEPENDENCY_WEAK)
                                continue;

                        /* Leave semaphores spinning on the other engines */
                        if (w->engine != rq->engine)
                                continue;

                        /* No waiter should start before its signaler */
                        GEM_BUG_ON(i915_request_has_initial_breadcrumb(w) &&
                                   __i915_request_has_started(w) &&
                                   !__i915_request_is_complete(rq));

                        if (!i915_request_is_ready(w))
                                continue;

                        if (rq_prio(w) < rq_prio(rq))
                                continue;

                        GEM_BUG_ON(rq_prio(w) > rq_prio(rq));
                        GEM_BUG_ON(i915_request_is_active(w));
                        list_move_tail(&w->sched.link, &list);
                }

                rq = list_first_entry_or_null(&list, typeof(*rq), sched.link);
        } while (rq);
}

static void defer_active(struct intel_engine_cs *engine)
{
        struct i915_request *rq;

        rq = __unwind_incomplete_requests(engine);
        if (!rq)
                return;

        defer_request(rq, i915_sched_lookup_priolist(engine->sched_engine,
                                                     rq_prio(rq)));
}

static bool
timeslice_yield(const struct intel_engine_execlists *el,
                const struct i915_request *rq)
{
        /*
         * Once bitten, forever smitten!
         *
         * If the active context ever busy-waited on a semaphore,
         * it will be treated as a hog until the end of its timeslice (i.e.
         * until it is scheduled out and replaced by a new submission,
         * possibly even its own lite-restore). The HW only sends an interrupt
         * on the first miss, and we do know if that semaphore has been
         * signaled, or even if it is now stuck on another semaphore. Play
         * safe, yield if it might be stuck -- it will be given a fresh
         * timeslice in the near future.
         */
        return rq->context->lrc.ccid == READ_ONCE(el->yield);
}

static bool needs_timeslice(const struct intel_engine_cs *engine,
                            const struct i915_request *rq)
{
        if (!intel_engine_has_timeslices(engine))
                return false;

        /* If not currently active, or about to switch, wait for next event */
        if (!rq || __i915_request_is_complete(rq))
                return false;

        /* We do not need to start the timeslice until after the ACK */
        if (READ_ONCE(engine->execlists.pending[0]))
                return false;

        /* If ELSP[1] is occupied, always check to see if worth slicing */
        if (!list_is_last_rcu(&rq->sched.link,
                              &engine->sched_engine->requests)) {
                ENGINE_TRACE(engine, "timeslice required for second inflight context\n");
                return true;
        }

        /* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */
        if (!i915_sched_engine_is_empty(engine->sched_engine)) {
                ENGINE_TRACE(engine, "timeslice required for queue\n");
                return true;
        }

        if (!RB_EMPTY_ROOT(&engine->execlists.virtual.rb_root)) {
                ENGINE_TRACE(engine, "timeslice required for virtual\n");
                return true;
        }

        return false;
}

static bool
timeslice_expired(struct intel_engine_cs *engine, const struct i915_request *rq)
{
        const struct intel_engine_execlists *el = &engine->execlists;

        if (i915_request_has_nopreempt(rq) && __i915_request_has_started(rq))
                return false;

        if (!needs_timeslice(engine, rq))
                return false;

        return timer_expired(&el->timer) || timeslice_yield(el, rq);
}

static unsigned long timeslice(const struct intel_engine_cs *engine)
{
        return READ_ONCE(engine->props.timeslice_duration_ms);
}

static void start_timeslice(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists *el = &engine->execlists;
        unsigned long duration;

        /* Disable the timer if there is nothing to switch to */
        duration = 0;
        if (needs_timeslice(engine, *el->active)) {
                /* Avoid continually prolonging an active timeslice */
                if (timer_active(&el->timer)) {
                        /*
                         * If we just submitted a new ELSP after an old
                         * context, that context may have already consumed
                         * its timeslice, so recheck.
                         */
                        if (!timer_pending(&el->timer))
                                tasklet_hi_schedule(&engine->sched_engine->tasklet);
                        return;
                }

                duration = timeslice(engine);
        }

        set_timer_ms(&el->timer, duration);
}

static void record_preemption(struct intel_engine_execlists *execlists)
{
        (void)I915_SELFTEST_ONLY(execlists->preempt_hang.count++);
}

static unsigned long active_preempt_timeout(struct intel_engine_cs *engine,
                                            const struct i915_request *rq)
{
        if (!rq)
                return 0;

        /* Force a fast reset for terminated contexts (ignoring sysfs!) */
        if (unlikely(intel_context_is_banned(rq->context) || bad_request(rq)))
                return 1;

        return READ_ONCE(engine->props.preempt_timeout_ms);
}

static void set_preempt_timeout(struct intel_engine_cs *engine,
                                const struct i915_request *rq)
{
        if (!intel_engine_has_preempt_reset(engine))
                return;

        set_timer_ms(&engine->execlists.preempt,
                     active_preempt_timeout(engine, rq));
}

static bool completed(const struct i915_request *rq)
{
        if (i915_request_has_sentinel(rq))
                return false;

        return __i915_request_is_complete(rq);
}

static void execlists_dequeue(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct i915_sched_engine * const sched_engine = engine->sched_engine;
        struct i915_request **port = execlists->pending;
        struct i915_request ** const last_port = port + execlists->port_mask;
        struct i915_request *last, * const *active;
        struct virtual_engine *ve;
        struct rb_node *rb;
        bool submit = false;

        /*
         * Hardware submission is through 2 ports. Conceptually each port
         * has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
         * static for a context, and unique to each, so we only execute
         * requests belonging to a single context from each ring. RING_HEAD
         * is maintained by the CS in the context image, it marks the place
         * where it got up to last time, and through RING_TAIL we tell the CS
         * where we want to execute up to this time.
         *
         * In this list the requests are in order of execution. Consecutive
         * requests from the same context are adjacent in the ringbuffer. We
         * can combine these requests into a single RING_TAIL update:
         *
         *              RING_HEAD...req1...req2
         *                                    ^- RING_TAIL
         * since to execute req2 the CS must first execute req1.
         *
         * Our goal then is to point each port to the end of a consecutive
         * sequence of requests as being the most optimal (fewest wake ups
         * and context switches) submission.
         */

        spin_lock(&sched_engine->lock);

        /*
         * If the queue is higher priority than the last
         * request in the currently active context, submit afresh.
         * We will resubmit again afterwards in case we need to split
         * the active context to interject the preemption request,
         * i.e. we will retrigger preemption following the ack in case
         * of trouble.
         *
         */
        active = execlists->active;
        while ((last = *active) && completed(last))
                active++;

        if (last) {
                if (need_preempt(engine, last)) {
                        ENGINE_TRACE(engine,
                                     "preempting last=%llx:%lld, prio=%d, hint=%d\n",
                                     last->fence.context,
                                     last->fence.seqno,
                                     last->sched.attr.priority,
                                     sched_engine->queue_priority_hint);
                        record_preemption(execlists);

                        /*
                         * Don't let the RING_HEAD advance past the breadcrumb
                         * as we unwind (and until we resubmit) so that we do
                         * not accidentally tell it to go backwards.
                         */
                        ring_set_paused(engine, 1);

                        /*
                         * Note that we have not stopped the GPU at this point,
                         * so we are unwinding the incomplete requests as they
                         * remain inflight and so by the time we do complete
                         * the preemption, some of the unwound requests may
                         * complete!
                         */
                        __unwind_incomplete_requests(engine);

                        last = NULL;
                } else if (timeslice_expired(engine, last)) {
                        ENGINE_TRACE(engine,
                                     "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n",
                                     str_yes_no(timer_expired(&execlists->timer)),
                                     last->fence.context, last->fence.seqno,
                                     rq_prio(last),
                                     sched_engine->queue_priority_hint,
                                     str_yes_no(timeslice_yield(execlists, last)));

                        /*
                         * Consume this timeslice; ensure we start a new one.
                         *
                         * The timeslice expired, and we will unwind the
                         * running contexts and recompute the next ELSP.
                         * If that submit will be the same pair of contexts
                         * (due to dependency ordering), we will skip the
                         * submission. If we don't cancel the timer now,
                         * we will see that the timer has expired and
                         * reschedule the tasklet; continually until the
                         * next context switch or other preeemption event.
                         *
                         * Since we have decided to reschedule based on
                         * consumption of this timeslice, if we submit the
                         * same context again, grant it a full timeslice.
                         */
                        cancel_timer(&execlists->timer);
                        ring_set_paused(engine, 1);
                        defer_active(engine);

                        /*
                         * Unlike for preemption, if we rewind and continue
                         * executing the same context as previously active,
                         * the order of execution will remain the same and
                         * the tail will only advance. We do not need to
                         * force a full context restore, as a lite-restore
                         * is sufficient to resample the monotonic TAIL.
                         *
                         * If we switch to any other context, similarly we
                         * will not rewind TAIL of current context, and
                         * normal save/restore will preserve state and allow
                         * us to later continue executing the same request.
                         */
                        last = NULL;
                } else {
                        /*
                         * Otherwise if we already have a request pending
                         * for execution after the current one, we can
                         * just wait until the next CS event before
                         * queuing more. In either case we will force a
                         * lite-restore preemption event, but if we wait
                         * we hopefully coalesce several updates into a single
                         * submission.
                         */
                        if (active[1]) {
                                /*
                                 * Even if ELSP[1] is occupied and not worthy
                                 * of timeslices, our queue might be.
                                 */
                                spin_unlock(&sched_engine->lock);
                                return;
                        }
                }
        }

        /* XXX virtual is always taking precedence */
        while ((ve = first_virtual_engine(engine))) {
                struct i915_request *rq;

                spin_lock(&ve->base.sched_engine->lock);

                rq = ve->request;
                if (unlikely(!virtual_matches(ve, rq, engine)))
                        goto unlock; /* lost the race to a sibling */

                GEM_BUG_ON(rq->engine != &ve->base);
                GEM_BUG_ON(rq->context != &ve->context);

                if (unlikely(rq_prio(rq) < queue_prio(sched_engine))) {
                        spin_unlock(&ve->base.sched_engine->lock);
                        break;
                }

                if (last && !can_merge_rq(last, rq)) {
                        spin_unlock(&ve->base.sched_engine->lock);
                        spin_unlock(&engine->sched_engine->lock);
                        return; /* leave this for another sibling */
                }

                ENGINE_TRACE(engine,
                             "virtual rq=%llx:%lld%s, new engine? %s\n",
                             rq->fence.context,
                             rq->fence.seqno,
                             __i915_request_is_complete(rq) ? "!" :
                             __i915_request_has_started(rq) ? "*" :
                             "",
                             str_yes_no(engine != ve->siblings[0]));

                WRITE_ONCE(ve->request, NULL);
                WRITE_ONCE(ve->base.sched_engine->queue_priority_hint, INT_MIN);

                rb = &ve->nodes[engine->id].rb;
                rb_erase_cached(rb, &execlists->virtual);
                RB_CLEAR_NODE(rb);

                GEM_BUG_ON(!(rq->execution_mask & engine->mask));
                WRITE_ONCE(rq->engine, engine);

                if (__i915_request_submit(rq)) {
                        /*
                         * Only after we confirm that we will submit
                         * this request (i.e. it has not already
                         * completed), do we want to update the context.
                         *
                         * This serves two purposes. It avoids
                         * unnecessary work if we are resubmitting an
                         * already completed request after timeslicing.
                         * But more importantly, it prevents us altering
                         * ve->siblings[] on an idle context, where
                         * we may be using ve->siblings[] in
                         * virtual_context_enter / virtual_context_exit.
                         */
                        virtual_xfer_context(ve, engine);
                        GEM_BUG_ON(ve->siblings[0] != engine);

                        submit = true;
                        last = rq;
                }

                i915_request_put(rq);
unlock:
                spin_unlock(&ve->base.sched_engine->lock);

                /*
                 * Hmm, we have a bunch of virtual engine requests,
                 * but the first one was already completed (thanks
                 * preempt-to-busy!). Keep looking at the veng queue
                 * until we have no more relevant requests (i.e.
                 * the normal submit queue has higher priority).
                 */
                if (submit)
                        break;
        }

        while ((rb = rb_first_cached(&sched_engine->queue))) {
                struct i915_priolist *p = to_priolist(rb);
                struct i915_request *rq, *rn;

                priolist_for_each_request_consume(rq, rn, p) {
                        bool merge = true;

                        /*
                         * Can we combine this request with the current port?
                         * It has to be the same context/ringbuffer and not
                         * have any exceptions (e.g. GVT saying never to
                         * combine contexts).
                         *
                         * If we can combine the requests, we can execute both
                         * by updating the RING_TAIL to point to the end of the
                         * second request, and so we never need to tell the
                         * hardware about the first.
                         */
                        if (last && !can_merge_rq(last, rq)) {
                                /*
                                 * If we are on the second port and cannot
                                 * combine this request with the last, then we
                                 * are done.
                                 */
                                if (port == last_port)
                                        goto done;

                                /*
                                 * We must not populate both ELSP[] with the
                                 * same LRCA, i.e. we must submit 2 different
                                 * contexts if we submit 2 ELSP.
                                 */
                                if (last->context == rq->context)
                                        goto done;

                                if (i915_request_has_sentinel(last))
                                        goto done;

                                /*
                                 * We avoid submitting virtual requests into
                                 * the secondary ports so that we can migrate
                                 * the request immediately to another engine
                                 * rather than wait for the primary request.
                                 */
                                if (rq->execution_mask != engine->mask)
                                        goto done;

                                /*
                                 * If GVT overrides us we only ever submit
                                 * port[0], leaving port[1] empty. Note that we
                                 * also have to be careful that we don't queue
                                 * the same context (even though a different
                                 * request) to the second port.
                                 */
                                if (ctx_single_port_submission(last->context) ||
                                    ctx_single_port_submission(rq->context))
                                        goto done;

                                merge = false;
                        }

                        if (__i915_request_submit(rq)) {
                                if (!merge) {
                                        *port++ = i915_request_get(last);
                                        last = NULL;
                                }

                                GEM_BUG_ON(last &&
                                           !can_merge_ctx(last->context,
                                                          rq->context));
                                GEM_BUG_ON(last &&
                                           i915_seqno_passed(last->fence.seqno,
                                                             rq->fence.seqno));

                                submit = true;
                                last = rq;
                        }
                }

                rb_erase_cached(&p->node, &sched_engine->queue);
                i915_priolist_free(p);
        }
done:
        *port++ = i915_request_get(last);

        /*
         * Here be a bit of magic! Or sleight-of-hand, whichever you prefer.
         *
         * We choose the priority hint such that if we add a request of greater
         * priority than this, we kick the submission tasklet to decide on
         * the right order of submitting the requests to hardware. We must
         * also be prepared to reorder requests as they are in-flight on the
         * HW. We derive the priority hint then as the first "hole" in
         * the HW submission ports and if there are no available slots,
         * the priority of the lowest executing request, i.e. last.
         *
         * When we do receive a higher priority request ready to run from the
         * user, see queue_request(), the priority hint is bumped to that
         * request triggering preemption on the next dequeue (or subsequent
         * interrupt for secondary ports).
         */
        sched_engine->queue_priority_hint = queue_prio(sched_engine);
        i915_sched_engine_reset_on_empty(sched_engine);
        spin_unlock(&sched_engine->lock);

        /*
         * We can skip poking the HW if we ended up with exactly the same set
         * of requests as currently running, e.g. trying to timeslice a pair
         * of ordered contexts.
         */
        if (submit &&
            memcmp(active,
                   execlists->pending,
                   (port - execlists->pending) * sizeof(*port))) {
                *port = NULL;
                while (port-- != execlists->pending)
                        execlists_schedule_in(*port, port - execlists->pending);

                WRITE_ONCE(execlists->yield, -1);
                set_preempt_timeout(engine, *active);
                execlists_submit_ports(engine);
        } else {
                ring_set_paused(engine, 0);
                while (port-- != execlists->pending)
                        i915_request_put(*port);
                *execlists->pending = NULL;
        }
}

static void execlists_dequeue_irq(struct intel_engine_cs *engine)
{
        local_irq_disable(); /* Suspend interrupts across request submission */
        execlists_dequeue(engine);
        local_irq_enable(); /* flush irq_work (e.g. breadcrumb enabling) */
}

static void clear_ports(struct i915_request **ports, int count)
{
        memset_p((void **)ports, NULL, count);
}

static void
copy_ports(struct i915_request **dst, struct i915_request **src, int count)
{
        /* A memcpy_p() would be very useful here! */
        while (count--)
                WRITE_ONCE(*dst++, *src++); /* avoid write tearing */
}

static struct i915_request **
cancel_port_requests(struct intel_engine_execlists * const execlists,
                     struct i915_request **inactive)
{
        struct i915_request * const *port;

        for (port = execlists->pending; *port; port++)
                *inactive++ = *port;
        clear_ports(execlists->pending, ARRAY_SIZE(execlists->pending));

        /* Mark the end of active before we overwrite *active */
        for (port = xchg(&execlists->active, execlists->pending); *port; port++)
                *inactive++ = *port;
        clear_ports(execlists->inflight, ARRAY_SIZE(execlists->inflight));

        smp_wmb(); /* complete the seqlock for execlists_active() */
        WRITE_ONCE(execlists->active, execlists->inflight);

        /* Having cancelled all outstanding process_csb(), stop their timers */
        GEM_BUG_ON(execlists->pending[0]);
        cancel_timer(&execlists->timer);
        cancel_timer(&execlists->preempt);

        return inactive;
}

static void invalidate_csb_entries(const u64 *first, const u64 *last)
{
        clflush((void *)first);
        clflush((void *)last);
}

/*
 * Starting with Gen12, the status has a new format:
 *
 *     bit  0:     switched to new queue
 *     bit  1:     reserved
 *     bit  2:     semaphore wait mode (poll or signal), only valid when
 *                 switch detail is set to "wait on semaphore"
 *     bits 3-5:   engine class
 *     bits 6-11:  engine instance
 *     bits 12-14: reserved
 *     bits 15-25: sw context id of the lrc the GT switched to
 *     bits 26-31: sw counter of the lrc the GT switched to
 *     bits 32-35: context switch detail
 *                  - 0: ctx complete
 *                  - 1: wait on sync flip
 *                  - 2: wait on vblank
 *                  - 3: wait on scanline
 *                  - 4: wait on semaphore
 *                  - 5: context preempted (not on SEMAPHORE_WAIT or
 *                       WAIT_FOR_EVENT)
 *     bit  36:    reserved
 *     bits 37-43: wait detail (for switch detail 1 to 4)
 *     bits 44-46: reserved
 *     bits 47-57: sw context id of the lrc the GT switched away from
 *     bits 58-63: sw counter of the lrc the GT switched away from
 *
 * Xe_HP csb shuffles things around compared to TGL:
 *
 *     bits 0-3:   context switch detail (same possible values as TGL)
 *     bits 4-9:   engine instance
 *     bits 10-25: sw context id of the lrc the GT switched to
 *     bits 26-31: sw counter of the lrc the GT switched to
 *     bit  32:    semaphore wait mode (poll or signal), Only valid when
 *                 switch detail is set to "wait on semaphore"
 *     bit  33:    switched to new queue
 *     bits 34-41: wait detail (for switch detail 1 to 4)
 *     bits 42-57: sw context id of the lrc the GT switched away from
 *     bits 58-63: sw counter of the lrc the GT switched away from
 */
static inline bool
__gen12_csb_parse(bool ctx_to_valid, bool ctx_away_valid, bool new_queue,
                  u8 switch_detail)
{
        /*
         * The context switch detail is not guaranteed to be 5 when a preemption
         * occurs, so we can't just check for that. The check below works for
         * all the cases we care about, including preemptions of WAIT
         * instructions and lite-restore. Preempt-to-idle via the CTRL register
         * would require some extra handling, but we don't support that.
         */
        if (!ctx_away_valid || new_queue) {
                GEM_BUG_ON(!ctx_to_valid);
                return true;
        }

        /*
         * switch detail = 5 is covered by the case above and we do not expect a
         * context switch on an unsuccessful wait instruction since we always
         * use polling mode.
         */
        GEM_BUG_ON(switch_detail);
        return false;
}

static bool xehp_csb_parse(const u64 csb)
{
        return __gen12_csb_parse(XEHP_CSB_CTX_VALID(lower_32_bits(csb)), /* cxt to */
                                 XEHP_CSB_CTX_VALID(upper_32_bits(csb)), /* cxt away */
                                 upper_32_bits(csb) & XEHP_CTX_STATUS_SWITCHED_TO_NEW_QUEUE,
                                 GEN12_CTX_SWITCH_DETAIL(lower_32_bits(csb)));
}

static bool gen12_csb_parse(const u64 csb)
{
        return __gen12_csb_parse(GEN12_CSB_CTX_VALID(lower_32_bits(csb)), /* cxt to */
                                 GEN12_CSB_CTX_VALID(upper_32_bits(csb)), /* cxt away */
                                 lower_32_bits(csb) & GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE,
                                 GEN12_CTX_SWITCH_DETAIL(upper_32_bits(csb)));
}

static bool gen8_csb_parse(const u64 csb)
{
        return csb & (GEN8_CTX_STATUS_IDLE_ACTIVE | GEN8_CTX_STATUS_PREEMPTED);
}

static noinline u64
wa_csb_read(const struct intel_engine_cs *engine, u64 * const csb)
{
        u64 entry;

        /*
         * Reading from the HWSP has one particular advantage: we can detect
         * a stale entry. Since the write into HWSP is broken, we have no reason
         * to trust the HW at all, the mmio entry may equally be unordered, so
         * we prefer the path that is self-checking and as a last resort,
         * return the mmio value.
         *
         * tgl,dg1:HSDES#22011327657
         */
        preempt_disable();
        if (wait_for_atomic_us((entry = READ_ONCE(*csb)) != -1, 10)) {
                int idx = csb - engine->execlists.csb_status;
                int status;

                status = GEN8_EXECLISTS_STATUS_BUF;
                if (idx >= 6) {
                        status = GEN11_EXECLISTS_STATUS_BUF2;
                        idx -= 6;
                }
                status += sizeof(u64) * idx;

                entry = intel_uncore_read64(engine->uncore,
                                            _MMIO(engine->mmio_base + status));
        }
        preempt_enable();

        return entry;
}

static u64 csb_read(const struct intel_engine_cs *engine, u64 * const csb)
{
        u64 entry = READ_ONCE(*csb);

        /*
         * Unfortunately, the GPU does not always serialise its write
         * of the CSB entries before its write of the CSB pointer, at least
         * from the perspective of the CPU, using what is known as a Global
         * Observation Point. We may read a new CSB tail pointer, but then
         * read the stale CSB entries, causing us to misinterpret the
         * context-switch events, and eventually declare the GPU hung.
         *
         * icl:HSDES#1806554093
         * tgl:HSDES#22011248461
         */
        if (unlikely(entry == -1))
                entry = wa_csb_read(engine, csb);

        /* Consume this entry so that we can spot its future reuse. */
        WRITE_ONCE(*csb, -1);

        /* ELSP is an implicit wmb() before the GPU wraps and overwrites csb */
        return entry;
}

static void new_timeslice(struct intel_engine_execlists *el)
{
        /* By cancelling, we will start afresh in start_timeslice() */
        cancel_timer(&el->timer);
}

static struct i915_request **
process_csb(struct intel_engine_cs *engine, struct i915_request **inactive)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        u64 * const buf = execlists->csb_status;
        const u8 num_entries = execlists->csb_size;
        struct i915_request **prev;
        u8 head, tail;

        /*
         * As we modify our execlists state tracking we require exclusive
         * access. Either we are inside the tasklet, or the tasklet is disabled
         * and we assume that is only inside the reset paths and so serialised.
         */
        GEM_BUG_ON(!tasklet_is_locked(&engine->sched_engine->tasklet) &&
                   !reset_in_progress(engine));

        /*
         * Note that csb_write, csb_status may be either in HWSP or mmio.
         * When reading from the csb_write mmio register, we have to be
         * careful to only use the GEN8_CSB_WRITE_PTR portion, which is
         * the low 4bits. As it happens we know the next 4bits are always
         * zero and so we can simply masked off the low u8 of the register
         * and treat it identically to reading from the HWSP (without having
         * to use explicit shifting and masking, and probably bifurcating
         * the code to handle the legacy mmio read).
         */
        head = execlists->csb_head;
        tail = READ_ONCE(*execlists->csb_write);
        if (unlikely(head == tail))
                return inactive;

        /*
         * We will consume all events from HW, or at least pretend to.
         *
         * The sequence of events from the HW is deterministic, and derived
         * from our writes to the ELSP, with a smidgen of variability for
         * the arrival of the asynchronous requests wrt to the inflight
         * execution. If the HW sends an event that does not correspond with
         * the one we are expecting, we have to abandon all hope as we lose
         * all tracking of what the engine is actually executing. We will
         * only detect we are out of sequence with the HW when we get an
         * 'impossible' event because we have already drained our own
         * preemption/promotion queue. If this occurs, we know that we likely
         * lost track of execution earlier and must unwind and restart, the
         * simplest way is by stop processing the event queue and force the
         * engine to reset.
         */
        execlists->csb_head = tail;
        ENGINE_TRACE(engine, "cs-irq head=%d, tail=%d\n", head, tail);

        /*
         * Hopefully paired with a wmb() in HW!
         *
         * We must complete the read of the write pointer before any reads
         * from the CSB, so that we do not see stale values. Without an rmb
         * (lfence) the HW may speculatively perform the CSB[] reads *before*
         * we perform the READ_ONCE(*csb_write).
         */
        rmb();

        /* Remember who was last running under the timer */
        prev = inactive;
        *prev = NULL;

        do {
                bool promote;
                u64 csb;

                if (++head == num_entries)
                        head = 0;

                /*
                 * We are flying near dragons again.
                 *
                 * We hold a reference to the request in execlist_port[]
                 * but no more than that. We are operating in softirq
                 * context and so cannot hold any mutex or sleep. That
                 * prevents us stopping the requests we are processing
                 * in port[] from being retired simultaneously (the
                 * breadcrumb will be complete before we see the
                 * context-switch). As we only hold the reference to the
                 * request, any pointer chasing underneath the request
                 * is subject to a potential use-after-free. Thus we
                 * store all of the bookkeeping within port[] as
                 * required, and avoid using unguarded pointers beneath
                 * request itself. The same applies to the atomic
                 * status notifier.
                 */

                csb = csb_read(engine, buf + head);
                ENGINE_TRACE(engine, "csb[%d]: status=0x%08x:0x%08x\n",
                             head, upper_32_bits(csb), lower_32_bits(csb));

                if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50))
                        promote = xehp_csb_parse(csb);
                else if (GRAPHICS_VER(engine->i915) >= 12)
                        promote = gen12_csb_parse(csb);
                else
                        promote = gen8_csb_parse(csb);
                if (promote) {
                        struct i915_request * const *old = execlists->active;

                        if (GEM_WARN_ON(!*execlists->pending)) {
                                execlists->error_interrupt |= ERROR_CSB;
                                break;
                        }

                        ring_set_paused(engine, 0);

                        /* Point active to the new ELSP; prevent overwriting */
                        WRITE_ONCE(execlists->active, execlists->pending);
                        smp_wmb(); /* notify execlists_active() */

                        /* cancel old inflight, prepare for switch */
                        trace_ports(execlists, "preempted", old);
                        while (*old)
                                *inactive++ = *old++;

                        /* switch pending to inflight */
                        GEM_BUG_ON(!assert_pending_valid(execlists, "promote"));
                        copy_ports(execlists->inflight,
                                   execlists->pending,
                                   execlists_num_ports(execlists));
                        smp_wmb(); /* complete the seqlock */
                        WRITE_ONCE(execlists->active, execlists->inflight);

                        /* XXX Magic delay for tgl */
                        ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);

                        WRITE_ONCE(execlists->pending[0], NULL);
                } else {
                        if (GEM_WARN_ON(!*execlists->active)) {
                                execlists->error_interrupt |= ERROR_CSB;
                                break;
                        }

                        /* port0 completed, advanced to port1 */
                        trace_ports(execlists, "completed", execlists->active);

                        /*
                         * We rely on the hardware being strongly
                         * ordered, that the breadcrumb write is
                         * coherent (visible from the CPU) before the
                         * user interrupt is processed. One might assume
                         * that the breadcrumb write being before the
                         * user interrupt and the CS event for the context
                         * switch would therefore be before the CS event
                         * itself...
                         */
                        if (GEM_SHOW_DEBUG() &&
                            !__i915_request_is_complete(*execlists->active)) {
                                struct i915_request *rq = *execlists->active;
                                const u32 *regs __maybe_unused =
                                        rq->context->lrc_reg_state;

                                ENGINE_TRACE(engine,
                                             "context completed before request!\n");
                                ENGINE_TRACE(engine,
                                             "ring:{start:0x%08x, head:%04x, tail:%04x, ctl:%08x, mode:%08x}\n",
                                             ENGINE_READ(engine, RING_START),
                                             ENGINE_READ(engine, RING_HEAD) & HEAD_ADDR,
                                             ENGINE_READ(engine, RING_TAIL) & TAIL_ADDR,
                                             ENGINE_READ(engine, RING_CTL),
                                             ENGINE_READ(engine, RING_MI_MODE));
                                ENGINE_TRACE(engine,
                                             "rq:{start:%08x, head:%04x, tail:%04x, seqno:%llx:%d, hwsp:%d}, ",
                                             i915_ggtt_offset(rq->ring->vma),
                                             rq->head, rq->tail,
                                             rq->fence.context,
                                             lower_32_bits(rq->fence.seqno),
                                             hwsp_seqno(rq));
                                ENGINE_TRACE(engine,
                                             "ctx:{start:%08x, head:%04x, tail:%04x}, ",
                                             regs[CTX_RING_START],
                                             regs[CTX_RING_HEAD],
                                             regs[CTX_RING_TAIL]);
                        }

                        *inactive++ = *execlists->active++;

                        GEM_BUG_ON(execlists->active - execlists->inflight >
                                   execlists_num_ports(execlists));
                }
        } while (head != tail);

        /*
         * Gen11 has proven to fail wrt global observation point between
         * entry and tail update, failing on the ordering and thus
         * we see an old entry in the context status buffer.
         *
         * Forcibly evict out entries for the next gpu csb update,
         * to increase the odds that we get a fresh entries with non
         * working hardware. The cost for doing so comes out mostly with
         * the wash as hardware, working or not, will need to do the
         * invalidation before.
         */
        invalidate_csb_entries(&buf[0], &buf[num_entries - 1]);

        /*
         * We assume that any event reflects a change in context flow
         * and merits a fresh timeslice. We reinstall the timer after
         * inspecting the queue to see if we need to resumbit.
         */
        if (*prev != *execlists->active) /* elide lite-restores */
                new_timeslice(execlists);

        return inactive;
}

static void post_process_csb(struct i915_request **port,
                             struct i915_request **last)
{
        while (port != last)
                execlists_schedule_out(*port++);
}

static void __execlists_hold(struct i915_request *rq)
{
        LIST_HEAD(list);

        do {
                struct i915_dependency *p;

                if (i915_request_is_active(rq))
                        __i915_request_unsubmit(rq);

                clear_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
                list_move_tail(&rq->sched.link,
                               &rq->engine->sched_engine->hold);
                i915_request_set_hold(rq);
                RQ_TRACE(rq, "on hold\n");

                for_each_waiter(p, rq) {
                        struct i915_request *w =
                                container_of(p->waiter, typeof(*w), sched);

                        if (p->flags & I915_DEPENDENCY_WEAK)
                                continue;

                        /* Leave semaphores spinning on the other engines */
                        if (w->engine != rq->engine)
                                continue;

                        if (!i915_request_is_ready(w))
                                continue;

                        if (__i915_request_is_complete(w))
                                continue;

                        if (i915_request_on_hold(w))
                                continue;

                        list_move_tail(&w->sched.link, &list);
                }

                rq = list_first_entry_or_null(&list, typeof(*rq), sched.link);
        } while (rq);
}

static bool execlists_hold(struct intel_engine_cs *engine,
                           struct i915_request *rq)
{
        if (i915_request_on_hold(rq))
                return false;

        spin_lock_irq(&engine->sched_engine->lock);

        if (__i915_request_is_complete(rq)) { /* too late! */
                rq = NULL;
                goto unlock;
        }

        /*
         * Transfer this request onto the hold queue to prevent it
         * being resumbitted to HW (and potentially completed) before we have
         * released it. Since we may have already submitted following
         * requests, we need to remove those as well.
         */
        GEM_BUG_ON(i915_request_on_hold(rq));
        GEM_BUG_ON(rq->engine != engine);
        __execlists_hold(rq);
        GEM_BUG_ON(list_empty(&engine->sched_engine->hold));

unlock:
        spin_unlock_irq(&engine->sched_engine->lock);
        return rq;
}

static bool hold_request(const struct i915_request *rq)
{
        struct i915_dependency *p;
        bool result = false;

        /*
         * If one of our ancestors is on hold, we must also be on hold,
         * otherwise we will bypass it and execute before it.
         */
        rcu_read_lock();
        for_each_signaler(p, rq) {
                const struct i915_request *s =
                        container_of(p->signaler, typeof(*s), sched);

                if (s->engine != rq->engine)
                        continue;

                result = i915_request_on_hold(s);
                if (result)
                        break;
        }
        rcu_read_unlock();

        return result;
}

static void __execlists_unhold(struct i915_request *rq)
{
        LIST_HEAD(list);

        do {
                struct i915_dependency *p;

                RQ_TRACE(rq, "hold release\n");

                GEM_BUG_ON(!i915_request_on_hold(rq));
                GEM_BUG_ON(!i915_sw_fence_signaled(&rq->submit));

                i915_request_clear_hold(rq);
                list_move_tail(&rq->sched.link,
                               i915_sched_lookup_priolist(rq->engine->sched_engine,
                                                          rq_prio(rq)));
                set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);

                /* Also release any children on this engine that are ready */
                for_each_waiter(p, rq) {
                        struct i915_request *w =
                                container_of(p->waiter, typeof(*w), sched);

                        if (p->flags & I915_DEPENDENCY_WEAK)
                                continue;

                        if (w->engine != rq->engine)
                                continue;

                        if (!i915_request_on_hold(w))
                                continue;

                        /* Check that no other parents are also on hold */
                        if (hold_request(w))
                                continue;

                        list_move_tail(&w->sched.link, &list);
                }

                rq = list_first_entry_or_null(&list, typeof(*rq), sched.link);
        } while (rq);
}

static void execlists_unhold(struct intel_engine_cs *engine,
                             struct i915_request *rq)
{
        spin_lock_irq(&engine->sched_engine->lock);

        /*
         * Move this request back to the priority queue, and all of its
         * children and grandchildren that were suspended along with it.
         */
        __execlists_unhold(rq);

        if (rq_prio(rq) > engine->sched_engine->queue_priority_hint) {
                engine->sched_engine->queue_priority_hint = rq_prio(rq);
                tasklet_hi_schedule(&engine->sched_engine->tasklet);
        }

        spin_unlock_irq(&engine->sched_engine->lock);
}

struct execlists_capture {
        struct work_struct work;
        struct i915_request *rq;
        struct i915_gpu_coredump *error;
};

static void execlists_capture_work(struct work_struct *work)
{
        struct execlists_capture *cap = container_of(work, typeof(*cap), work);
        const gfp_t gfp = __GFP_KSWAPD_RECLAIM | __GFP_RETRY_MAYFAIL |
                __GFP_NOWARN;
        struct intel_engine_cs *engine = cap->rq->engine;
        struct intel_gt_coredump *gt = cap->error->gt;
        struct intel_engine_capture_vma *vma;

        /* Compress all the objects attached to the request, slow! */
        vma = intel_engine_coredump_add_request(gt->engine, cap->rq, gfp);
        if (vma) {
                struct i915_vma_compress *compress =
                        i915_vma_capture_prepare(gt);

                intel_engine_coredump_add_vma(gt->engine, vma, compress);
                i915_vma_capture_finish(gt, compress);
        }

        gt->simulated = gt->engine->simulated;
        cap->error->simulated = gt->simulated;

        /* Publish the error state, and announce it to the world */
        i915_error_state_store(cap->error);
        i915_gpu_coredump_put(cap->error);

        /* Return this request and all that depend upon it for signaling */
        execlists_unhold(engine, cap->rq);
        i915_request_put(cap->rq);

        kfree(cap);
}

static struct execlists_capture *capture_regs(struct intel_engine_cs *engine)
{
        const gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
        struct execlists_capture *cap;

        cap = kmalloc(sizeof(*cap), gfp);
        if (!cap)
                return NULL;

        cap->error = i915_gpu_coredump_alloc(engine->i915, gfp);
        if (!cap->error)
                goto err_cap;

        cap->error->gt = intel_gt_coredump_alloc(engine->gt, gfp);
        if (!cap->error->gt)
                goto err_gpu;

        cap->error->gt->engine = intel_engine_coredump_alloc(engine, gfp);
        if (!cap->error->gt->engine)
                goto err_gt;

        cap->error->gt->engine->hung = true;

        return cap;

err_gt:
        kfree(cap->error->gt);
err_gpu:
        kfree(cap->error);
err_cap:
        kfree(cap);
        return NULL;
}

static struct i915_request *
active_context(struct intel_engine_cs *engine, u32 ccid)
{
        const struct intel_engine_execlists * const el = &engine->execlists;
        struct i915_request * const *port, *rq;

        /*
         * Use the most recent result from process_csb(), but just in case
         * we trigger an error (via interrupt) before the first CS event has
         * been written, peek at the next submission.
         */

        for (port = el->active; (rq = *port); port++) {
                if (rq->context->lrc.ccid == ccid) {
                        ENGINE_TRACE(engine,
                                     "ccid:%x found at active:%zd\n",
                                     ccid, port - el->active);
                        return rq;
                }
        }

        for (port = el->pending; (rq = *port); port++) {
                if (rq->context->lrc.ccid == ccid) {
                        ENGINE_TRACE(engine,
                                     "ccid:%x found at pending:%zd\n",
                                     ccid, port - el->pending);
                        return rq;
                }
        }

        ENGINE_TRACE(engine, "ccid:%x not found\n", ccid);
        return NULL;
}

static u32 active_ccid(struct intel_engine_cs *engine)
{
        return ENGINE_READ_FW(engine, RING_EXECLIST_STATUS_HI);
}

static void execlists_capture(struct intel_engine_cs *engine)
{
        struct execlists_capture *cap;

        if (!IS_ENABLED(CONFIG_DRM_I915_CAPTURE_ERROR))
                return;

        /*
         * We need to _quickly_ capture the engine state before we reset.
         * We are inside an atomic section (softirq) here and we are delaying
         * the forced preemption event.
         */
        cap = capture_regs(engine);
        if (!cap)
                return;

        spin_lock_irq(&engine->sched_engine->lock);
        cap->rq = active_context(engine, active_ccid(engine));
        if (cap->rq) {
                cap->rq = active_request(cap->rq->context->timeline, cap->rq);
                cap->rq = i915_request_get_rcu(cap->rq);
        }
        spin_unlock_irq(&engine->sched_engine->lock);
        if (!cap->rq)
                goto err_free;

        /*
         * Remove the request from the execlists queue, and take ownership
         * of the request. We pass it to our worker who will _slowly_ compress
         * all the pages the _user_ requested for debugging their batch, after
         * which we return it to the queue for signaling.
         *
         * By removing them from the execlists queue, we also remove the
         * requests from being processed by __unwind_incomplete_requests()
         * during the intel_engine_reset(), and so they will *not* be replayed
         * afterwards.
         *
         * Note that because we have not yet reset the engine at this point,
         * it is possible for the request that we have identified as being
         * guilty, did in fact complete and we will then hit an arbitration
         * point allowing the outstanding preemption to succeed. The likelihood
         * of that is very low (as capturing of the engine registers should be
         * fast enough to run inside an irq-off atomic section!), so we will
         * simply hold that request accountable for being non-preemptible
         * long enough to force the reset.
         */
        if (!execlists_hold(engine, cap->rq))
                goto err_rq;

        INIT_WORK(&cap->work, execlists_capture_work);
        schedule_work(&cap->work);
        return;

err_rq:
        i915_request_put(cap->rq);
err_free:
        i915_gpu_coredump_put(cap->error);
        kfree(cap);
}

static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
{
        const unsigned int bit = I915_RESET_ENGINE + engine->id;
        unsigned long *lock = &engine->gt->reset.flags;

        if (!intel_has_reset_engine(engine->gt))
                return;

        if (test_and_set_bit(bit, lock))
                return;

        ENGINE_TRACE(engine, "reset for %s\n", msg);

        /* Mark this tasklet as disabled to avoid waiting for it to complete */
        tasklet_disable_nosync(&engine->sched_engine->tasklet);

        ring_set_paused(engine, 1); /* Freeze the current request in place */
        execlists_capture(engine);
        intel_engine_reset(engine, msg);

        tasklet_enable(&engine->sched_engine->tasklet);
        clear_and_wake_up_bit(bit, lock);
}

static bool preempt_timeout(const struct intel_engine_cs *const engine)
{
        const struct timer_list *t = &engine->execlists.preempt;

        if (!CONFIG_DRM_I915_PREEMPT_TIMEOUT)
                return false;

        if (!timer_expired(t))
                return false;

        return engine->execlists.pending[0];
}

/*
 * Check the unread Context Status Buffers and manage the submission of new
 * contexts to the ELSP accordingly.
 */
static void execlists_submission_tasklet(struct tasklet_struct *t)
{
        struct i915_sched_engine *sched_engine =
                from_tasklet(sched_engine, t, tasklet);
        struct intel_engine_cs * const engine = sched_engine->private_data;
        struct i915_request *post[2 * EXECLIST_MAX_PORTS];
        struct i915_request **inactive;

        rcu_read_lock();
        inactive = process_csb(engine, post);
        GEM_BUG_ON(inactive - post > ARRAY_SIZE(post));

        if (unlikely(preempt_timeout(engine))) {
                cancel_timer(&engine->execlists.preempt);
                engine->execlists.error_interrupt |= ERROR_PREEMPT;
        }

        if (unlikely(READ_ONCE(engine->execlists.error_interrupt))) {
                const char *msg;

                /* Generate the error message in priority wrt to the user! */
                if (engine->execlists.error_interrupt & GENMASK(15, 0))
                        msg = "CS error"; /* thrown by a user payload */
                else if (engine->execlists.error_interrupt & ERROR_CSB)
                        msg = "invalid CSB event";
                else if (engine->execlists.error_interrupt & ERROR_PREEMPT)
                        msg = "preemption time out";
                else
                        msg = "internal error";

                engine->execlists.error_interrupt = 0;
                execlists_reset(engine, msg);
        }

        if (!engine->execlists.pending[0]) {
                execlists_dequeue_irq(engine);
                start_timeslice(engine);
        }

        post_process_csb(post, inactive);
        rcu_read_unlock();
}

static void execlists_irq_handler(struct intel_engine_cs *engine, u16 iir)
{
        bool tasklet = false;

        if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
                u32 eir;

                /* Upper 16b are the enabling mask, rsvd for internal errors */
                eir = ENGINE_READ(engine, RING_EIR) & GENMASK(15, 0);
                ENGINE_TRACE(engine, "CS error: %x\n", eir);

                /* Disable the error interrupt until after the reset */
                if (likely(eir)) {
                        ENGINE_WRITE(engine, RING_EMR, ~0u);
                        ENGINE_WRITE(engine, RING_EIR, eir);
                        WRITE_ONCE(engine->execlists.error_interrupt, eir);
                        tasklet = true;
                }
        }

        if (iir & GT_WAIT_SEMAPHORE_INTERRUPT) {
                WRITE_ONCE(engine->execlists.yield,
                           ENGINE_READ_FW(engine, RING_EXECLIST_STATUS_HI));
                ENGINE_TRACE(engine, "semaphore yield: %08x\n",
                             engine->execlists.yield);
                if (del_timer(&engine->execlists.timer))
                        tasklet = true;
        }

        if (iir & GT_CONTEXT_SWITCH_INTERRUPT)
                tasklet = true;

        if (iir & GT_RENDER_USER_INTERRUPT)
                intel_engine_signal_breadcrumbs(engine);

        if (tasklet)
                tasklet_hi_schedule(&engine->sched_engine->tasklet);
}

static void __execlists_kick(struct intel_engine_execlists *execlists)
{
        struct intel_engine_cs *engine =
                container_of(execlists, typeof(*engine), execlists);

        /* Kick the tasklet for some interrupt coalescing and reset handling */
        tasklet_hi_schedule(&engine->sched_engine->tasklet);
}

#define execlists_kick(t, member) \
        __execlists_kick(container_of(t, struct intel_engine_execlists, member))

static void execlists_timeslice(struct timer_list *timer)
{
        execlists_kick(timer, timer);
}

static void execlists_preempt(struct timer_list *timer)
{
        execlists_kick(timer, preempt);
}

static void queue_request(struct intel_engine_cs *engine,
                          struct i915_request *rq)
{
        GEM_BUG_ON(!list_empty(&rq->sched.link));
        list_add_tail(&rq->sched.link,
                      i915_sched_lookup_priolist(engine->sched_engine,
                                                 rq_prio(rq)));
        set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
}

static bool submit_queue(struct intel_engine_cs *engine,
                         const struct i915_request *rq)
{
        struct i915_sched_engine *sched_engine = engine->sched_engine;

        if (rq_prio(rq) <= sched_engine->queue_priority_hint)
                return false;

        sched_engine->queue_priority_hint = rq_prio(rq);
        return true;
}

static bool ancestor_on_hold(const struct intel_engine_cs *engine,
                             const struct i915_request *rq)
{
        GEM_BUG_ON(i915_request_on_hold(rq));
        return !list_empty(&engine->sched_engine->hold) && hold_request(rq);
}

static void execlists_submit_request(struct i915_request *request)
{
        struct intel_engine_cs *engine = request->engine;
        unsigned long flags;

        /* Will be called from irq-context when using foreign fences. */
        spin_lock_irqsave(&engine->sched_engine->lock, flags);

        if (unlikely(ancestor_on_hold(engine, request))) {
                RQ_TRACE(request, "ancestor on hold\n");
                list_add_tail(&request->sched.link,
                              &engine->sched_engine->hold);
                i915_request_set_hold(request);
        } else {
                queue_request(engine, request);

                GEM_BUG_ON(i915_sched_engine_is_empty(engine->sched_engine));
                GEM_BUG_ON(list_empty(&request->sched.link));

                if (submit_queue(engine, request))
                        __execlists_kick(&engine->execlists);
        }

        spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
}

static int
__execlists_context_pre_pin(struct intel_context *ce,
                            struct intel_engine_cs *engine,
                            struct i915_gem_ww_ctx *ww, void **vaddr)
{
        int err;

        err = lrc_pre_pin(ce, engine, ww, vaddr);
        if (err)
                return err;

        if (!__test_and_set_bit(CONTEXT_INIT_BIT, &ce->flags)) {
                lrc_init_state(ce, engine, *vaddr);

                __i915_gem_object_flush_map(ce->state->obj, 0, engine->context_size);
        }

        return 0;
}

static int execlists_context_pre_pin(struct intel_context *ce,
                                     struct i915_gem_ww_ctx *ww,
                                     void **vaddr)
{
        return __execlists_context_pre_pin(ce, ce->engine, ww, vaddr);
}

static int execlists_context_pin(struct intel_context *ce, void *vaddr)
{
        return lrc_pin(ce, ce->engine, vaddr);
}

static int execlists_context_alloc(struct intel_context *ce)
{
        return lrc_alloc(ce, ce->engine);
}

static void execlists_context_cancel_request(struct intel_context *ce,
                                             struct i915_request *rq)
{
        struct intel_engine_cs *engine = NULL;

        i915_request_active_engine(rq, &engine);

        if (engine && intel_engine_pulse(engine))
                intel_gt_handle_error(engine->gt, engine->mask, 0,
                                      "request cancellation by %s",
                                      current->comm);
}

static struct intel_context *
execlists_create_parallel(struct intel_engine_cs **engines,
                          unsigned int num_siblings,
                          unsigned int width)
{
        struct intel_context *parent = NULL, *ce, *err;
        int i;

        GEM_BUG_ON(num_siblings != 1);

        for (i = 0; i < width; ++i) {
                ce = intel_context_create(engines[i]);
                if (IS_ERR(ce)) {
                        err = ce;
                        goto unwind;
                }

                if (i == 0)
                        parent = ce;
                else
                        intel_context_bind_parent_child(parent, ce);
        }

        parent->parallel.fence_context = dma_fence_context_alloc(1);

        intel_context_set_nopreempt(parent);
        for_each_child(parent, ce)
                intel_context_set_nopreempt(ce);

        return parent;

unwind:
        if (parent)
                intel_context_put(parent);
        return err;
}

static const struct intel_context_ops execlists_context_ops = {
        .flags = COPS_HAS_INFLIGHT,

        .alloc = execlists_context_alloc,

        .cancel_request = execlists_context_cancel_request,

        .pre_pin = execlists_context_pre_pin,
        .pin = execlists_context_pin,
        .unpin = lrc_unpin,
        .post_unpin = lrc_post_unpin,

        .enter = intel_context_enter_engine,
        .exit = intel_context_exit_engine,

        .reset = lrc_reset,
        .destroy = lrc_destroy,

        .create_parallel = execlists_create_parallel,
        .create_virtual = execlists_create_virtual,
};

static int emit_pdps(struct i915_request *rq)
{
        const struct intel_engine_cs * const engine = rq->engine;
        struct i915_ppgtt * const ppgtt = i915_vm_to_ppgtt(rq->context->vm);
        int err, i;
        u32 *cs;

        GEM_BUG_ON(intel_vgpu_active(rq->engine->i915));

        /*
         * Beware ye of the dragons, this sequence is magic!
         *
         * Small changes to this sequence can cause anything from
         * GPU hangs to forcewake errors and machine lockups!
         */

        cs = intel_ring_begin(rq, 2);
        if (IS_ERR(cs))
                return PTR_ERR(cs);

        *cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
        *cs++ = MI_NOOP;
        intel_ring_advance(rq, cs);

        /* Flush any residual operations from the context load */
        err = engine->emit_flush(rq, EMIT_FLUSH);
        if (err)
                return err;

        /* Magic required to prevent forcewake errors! */
        err = engine->emit_flush(rq, EMIT_INVALIDATE);
        if (err)
                return err;

        cs = intel_ring_begin(rq, 4 * GEN8_3LVL_PDPES + 2);
        if (IS_ERR(cs))
                return PTR_ERR(cs);

        /* Ensure the LRI have landed before we invalidate & continue */
        *cs++ = MI_LOAD_REGISTER_IMM(2 * GEN8_3LVL_PDPES) | MI_LRI_FORCE_POSTED;
        for (i = GEN8_3LVL_PDPES; i--; ) {
                const dma_addr_t pd_daddr = i915_page_dir_dma_addr(ppgtt, i);
                u32 base = engine->mmio_base;

                *cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_UDW(base, i));
                *cs++ = upper_32_bits(pd_daddr);
                *cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_LDW(base, i));
                *cs++ = lower_32_bits(pd_daddr);
        }
        *cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
        intel_ring_advance(rq, cs);

        intel_ring_advance(rq, cs);

        return 0;
}

static int execlists_request_alloc(struct i915_request *request)
{
        int ret;

        GEM_BUG_ON(!intel_context_is_pinned(request->context));

        /*
         * Flush enough space to reduce the likelihood of waiting after
         * we start building the request - in which case we will just
         * have to repeat work.
         */
        request->reserved_space += EXECLISTS_REQUEST_SIZE;

        /*
         * Note that after this point, we have committed to using
         * this request as it is being used to both track the
         * state of engine initialisation and liveness of the
         * golden renderstate above. Think twice before you try
         * to cancel/unwind this request now.
         */

        if (!i915_vm_is_4lvl(request->context->vm)) {
                ret = emit_pdps(request);
                if (ret)
                        return ret;
        }

        /* Unconditionally invalidate GPU caches and TLBs. */
        ret = request->engine->emit_flush(request, EMIT_INVALIDATE);
        if (ret)
                return ret;

        request->reserved_space -= EXECLISTS_REQUEST_SIZE;
        return 0;
}

static void reset_csb_pointers(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        const unsigned int reset_value = execlists->csb_size - 1;

        ring_set_paused(engine, 0);

        /*
         * Sometimes Icelake forgets to reset its pointers on a GPU reset.
         * Bludgeon them with a mmio update to be sure.
         */
        ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
                     0xffff << 16 | reset_value << 8 | reset_value);
        ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);

        /*
         * After a reset, the HW starts writing into CSB entry [0]. We
         * therefore have to set our HEAD pointer back one entry so that
         * the *first* entry we check is entry 0. To complicate this further,
         * as we don't wait for the first interrupt after reset, we have to
         * fake the HW write to point back to the last entry so that our
         * inline comparison of our cached head position against the last HW
         * write works even before the first interrupt.
         */
        execlists->csb_head = reset_value;
        WRITE_ONCE(*execlists->csb_write, reset_value);
        wmb(); /* Make sure this is visible to HW (paranoia?) */

        /* Check that the GPU does indeed update the CSB entries! */
        memset(execlists->csb_status, -1, (reset_value + 1) * sizeof(u64));
        invalidate_csb_entries(&execlists->csb_status[0],
                               &execlists->csb_status[reset_value]);

        /* Once more for luck and our trusty paranoia */
        ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
                     0xffff << 16 | reset_value << 8 | reset_value);
        ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);

        GEM_BUG_ON(READ_ONCE(*execlists->csb_write) != reset_value);
}

static void sanitize_hwsp(struct intel_engine_cs *engine)
{
        struct intel_timeline *tl;

        list_for_each_entry(tl, &engine->status_page.timelines, engine_link)
                intel_timeline_reset_seqno(tl);
}

static void execlists_sanitize(struct intel_engine_cs *engine)
{
        GEM_BUG_ON(execlists_active(&engine->execlists));

        /*
         * Poison residual state on resume, in case the suspend didn't!
         *
         * We have to assume that across suspend/resume (or other loss
         * of control) that the contents of our pinned buffers has been
         * lost, replaced by garbage. Since this doesn't always happen,
         * let's poison such state so that we more quickly spot when
         * we falsely assume it has been preserved.
         */
        if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
                memset(engine->status_page.addr, POISON_INUSE, PAGE_SIZE);

        reset_csb_pointers(engine);

        /*
         * The kernel_context HWSP is stored in the status_page. As above,
         * that may be lost on resume/initialisation, and so we need to
         * reset the value in the HWSP.
         */
        sanitize_hwsp(engine);

        /* And scrub the dirty cachelines for the HWSP */
        clflush_cache_range(engine->status_page.addr, PAGE_SIZE);

        intel_engine_reset_pinned_contexts(engine);
}

static void enable_error_interrupt(struct intel_engine_cs *engine)
{
        u32 status;

        engine->execlists.error_interrupt = 0;
        ENGINE_WRITE(engine, RING_EMR, ~0u);
        ENGINE_WRITE(engine, RING_EIR, ~0u); /* clear all existing errors */

        status = ENGINE_READ(engine, RING_ESR);
        if (unlikely(status)) {
                drm_err(&engine->i915->drm,
                        "engine '%s' resumed still in error: %08x\n",
                        engine->name, status);
                __intel_gt_reset(engine->gt, engine->mask);
        }

        /*
         * On current gen8+, we have 2 signals to play with
         *
         * - I915_ERROR_INSTUCTION (bit 0)
         *
         *    Generate an error if the command parser encounters an invalid
         *    instruction
         *
         *    This is a fatal error.
         *
         * - CP_PRIV (bit 2)
         *
         *    Generate an error on privilege violation (where the CP replaces
         *    the instruction with a no-op). This also fires for writes into
         *    read-only scratch pages.
         *
         *    This is a non-fatal error, parsing continues.
         *
         * * there are a few others defined for odd HW that we do not use
         *
         * Since CP_PRIV fires for cases where we have chosen to ignore the
         * error (as the HW is validating and suppressing the mistakes), we
         * only unmask the instruction error bit.
         */
        ENGINE_WRITE(engine, RING_EMR, ~I915_ERROR_INSTRUCTION);
}

static void enable_execlists(struct intel_engine_cs *engine)
{
        u32 mode;

        assert_forcewakes_active(engine->uncore, FORCEWAKE_ALL);

        intel_engine_set_hwsp_writemask(engine, ~0u); /* HWSTAM */

        if (GRAPHICS_VER(engine->i915) >= 11)
                mode = _MASKED_BIT_ENABLE(GEN11_GFX_DISABLE_LEGACY_MODE);
        else
                mode = _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE);
        ENGINE_WRITE_FW(engine, RING_MODE_GEN7, mode);

        ENGINE_WRITE_FW(engine, RING_MI_MODE, _MASKED_BIT_DISABLE(STOP_RING));

        ENGINE_WRITE_FW(engine,
                        RING_HWS_PGA,
                        i915_ggtt_offset(engine->status_page.vma));
        ENGINE_POSTING_READ(engine, RING_HWS_PGA);

        enable_error_interrupt(engine);
}

static int execlists_resume(struct intel_engine_cs *engine)
{
        intel_mocs_init_engine(engine);
        intel_breadcrumbs_reset(engine->breadcrumbs);

        enable_execlists(engine);

        if (engine->class == RENDER_CLASS)
                xehp_enable_ccs_engines(engine);

        return 0;
}

static void execlists_reset_prepare(struct intel_engine_cs *engine)
{
        ENGINE_TRACE(engine, "depth<-%d\n",
                     atomic_read(&engine->sched_engine->tasklet.count));

        /*
         * Prevent request submission to the hardware until we have
         * completed the reset in i915_gem_reset_finish(). If a request
         * is completed by one engine, it may then queue a request
         * to a second via its execlists->tasklet *just* as we are
         * calling engine->resume() and also writing the ELSP.
         * Turning off the execlists->tasklet until the reset is over
         * prevents the race.
         */
        __tasklet_disable_sync_once(&engine->sched_engine->tasklet);
        GEM_BUG_ON(!reset_in_progress(engine));

        /*
         * We stop engines, otherwise we might get failed reset and a
         * dead gpu (on elk). Also as modern gpu as kbl can suffer
         * from system hang if batchbuffer is progressing when
         * the reset is issued, regardless of READY_TO_RESET ack.
         * Thus assume it is best to stop engines on all gens
         * where we have a gpu reset.
         *
         * WaKBLVECSSemaphoreWaitPoll:kbl (on ALL_ENGINES)
         *
         * FIXME: Wa for more modern gens needs to be validated
         */
        ring_set_paused(engine, 1);
        intel_engine_stop_cs(engine);

        engine->execlists.reset_ccid = active_ccid(engine);
}

static struct i915_request **
reset_csb(struct intel_engine_cs *engine, struct i915_request **inactive)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;

        mb(); /* paranoia: read the CSB pointers from after the reset */
        clflush(execlists->csb_write);
        mb();

        inactive = process_csb(engine, inactive); /* drain preemption events */

        /* Following the reset, we need to reload the CSB read/write pointers */
        reset_csb_pointers(engine);

        return inactive;
}

static void
execlists_reset_active(struct intel_engine_cs *engine, bool stalled)
{
        struct intel_context *ce;
        struct i915_request *rq;
        u32 head;

        /*
         * Save the currently executing context, even if we completed
         * its request, it was still running at the time of the
         * reset and will have been clobbered.
         */
        rq = active_context(engine, engine->execlists.reset_ccid);
        if (!rq)
                return;

        ce = rq->context;
        GEM_BUG_ON(!i915_vma_is_pinned(ce->state));

        if (__i915_request_is_complete(rq)) {
                /* Idle context; tidy up the ring so we can restart afresh */
                head = intel_ring_wrap(ce->ring, rq->tail);
                goto out_replay;
        }

        /* We still have requests in-flight; the engine should be active */
        GEM_BUG_ON(!intel_engine_pm_is_awake(engine));

        /* Context has requests still in-flight; it should not be idle! */
        GEM_BUG_ON(i915_active_is_idle(&ce->active));

        rq = active_request(ce->timeline, rq);
        head = intel_ring_wrap(ce->ring, rq->head);
        GEM_BUG_ON(head == ce->ring->tail);

        /*
         * If this request hasn't started yet, e.g. it is waiting on a
         * semaphore, we need to avoid skipping the request or else we
         * break the signaling chain. However, if the context is corrupt
         * the request will not restart and we will be stuck with a wedged
         * device. It is quite often the case that if we issue a reset
         * while the GPU is loading the context image, that the context
         * image becomes corrupt.
         *
         * Otherwise, if we have not started yet, the request should replay
         * perfectly and we do not need to flag the result as being erroneous.
         */
        if (!__i915_request_has_started(rq))
                goto out_replay;

        /*
         * If the request was innocent, we leave the request in the ELSP
         * and will try to replay it on restarting. The context image may
         * have been corrupted by the reset, in which case we may have
         * to service a new GPU hang, but more likely we can continue on
         * without impact.
         *
         * If the request was guilty, we presume the context is corrupt
         * and have to at least restore the RING register in the context
         * image back to the expected values to skip over the guilty request.
         */
        __i915_request_reset(rq, stalled);

        /*
         * We want a simple context + ring to execute the breadcrumb update.
         * We cannot rely on the context being intact across the GPU hang,
         * so clear it and rebuild just what we need for the breadcrumb.
         * All pending requests for this context will be zapped, and any
         * future request will be after userspace has had the opportunity
         * to recreate its own state.
         */
out_replay:
        ENGINE_TRACE(engine, "replay {head:%04x, tail:%04x}\n",
                     head, ce->ring->tail);
        lrc_reset_regs(ce, engine);
        ce->lrc.lrca = lrc_update_regs(ce, engine, head);
}

static void execlists_reset_csb(struct intel_engine_cs *engine, bool stalled)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct i915_request *post[2 * EXECLIST_MAX_PORTS];
        struct i915_request **inactive;

        rcu_read_lock();
        inactive = reset_csb(engine, post);

        execlists_reset_active(engine, true);

        inactive = cancel_port_requests(execlists, inactive);
        post_process_csb(post, inactive);
        rcu_read_unlock();
}

static void execlists_reset_rewind(struct intel_engine_cs *engine, bool stalled)
{
        unsigned long flags;

        ENGINE_TRACE(engine, "\n");

        /* Process the csb, find the guilty context and throw away */
        execlists_reset_csb(engine, stalled);

        /* Push back any incomplete requests for replay after the reset. */
        rcu_read_lock();
        spin_lock_irqsave(&engine->sched_engine->lock, flags);
        __unwind_incomplete_requests(engine);
        spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
        rcu_read_unlock();
}

static void nop_submission_tasklet(struct tasklet_struct *t)
{
        struct i915_sched_engine *sched_engine =
                from_tasklet(sched_engine, t, tasklet);
        struct intel_engine_cs * const engine = sched_engine->private_data;

        /* The driver is wedged; don't process any more events. */
        WRITE_ONCE(engine->sched_engine->queue_priority_hint, INT_MIN);
}

static void execlists_reset_cancel(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct i915_sched_engine * const sched_engine = engine->sched_engine;
        struct i915_request *rq, *rn;
        struct rb_node *rb;
        unsigned long flags;

        ENGINE_TRACE(engine, "\n");

        /*
         * Before we call engine->cancel_requests(), we should have exclusive
         * access to the submission state. This is arranged for us by the
         * caller disabling the interrupt generation, the tasklet and other
         * threads that may then access the same state, giving us a free hand
         * to reset state. However, we still need to let lockdep be aware that
         * we know this state may be accessed in hardirq context, so we
         * disable the irq around this manipulation and we want to keep
         * the spinlock focused on its duties and not accidentally conflate
         * coverage to the submission's irq state. (Similarly, although we
         * shouldn't need to disable irq around the manipulation of the
         * submission's irq state, we also wish to remind ourselves that
         * it is irq state.)
         */
        execlists_reset_csb(engine, true);

        rcu_read_lock();
        spin_lock_irqsave(&engine->sched_engine->lock, flags);

        /* Mark all executing requests as skipped. */
        list_for_each_entry(rq, &engine->sched_engine->requests, sched.link)
                i915_request_put(i915_request_mark_eio(rq));
        intel_engine_signal_breadcrumbs(engine);

        /* Flush the queued requests to the timeline list (for retiring). */
        while ((rb = rb_first_cached(&sched_engine->queue))) {
                struct i915_priolist *p = to_priolist(rb);

                priolist_for_each_request_consume(rq, rn, p) {
                        if (i915_request_mark_eio(rq)) {
                                __i915_request_submit(rq);
                                i915_request_put(rq);
                        }
                }

                rb_erase_cached(&p->node, &sched_engine->queue);
                i915_priolist_free(p);
        }

        /* On-hold requests will be flushed to timeline upon their release */
        list_for_each_entry(rq, &sched_engine->hold, sched.link)
                i915_request_put(i915_request_mark_eio(rq));

        /* Cancel all attached virtual engines */
        while ((rb = rb_first_cached(&execlists->virtual))) {
                struct virtual_engine *ve =
                        rb_entry(rb, typeof(*ve), nodes[engine->id].rb);

                rb_erase_cached(rb, &execlists->virtual);
                RB_CLEAR_NODE(rb);

                spin_lock(&ve->base.sched_engine->lock);
                rq = fetch_and_zero(&ve->request);
                if (rq) {
                        if (i915_request_mark_eio(rq)) {
                                rq->engine = engine;
                                __i915_request_submit(rq);
                                i915_request_put(rq);
                        }
                        i915_request_put(rq);

                        ve->base.sched_engine->queue_priority_hint = INT_MIN;
                }
                spin_unlock(&ve->base.sched_engine->lock);
        }

        /* Remaining _unready_ requests will be nop'ed when submitted */

        sched_engine->queue_priority_hint = INT_MIN;
        sched_engine->queue = RB_ROOT_CACHED;

        GEM_BUG_ON(__tasklet_is_enabled(&engine->sched_engine->tasklet));
        engine->sched_engine->tasklet.callback = nop_submission_tasklet;

        spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
        rcu_read_unlock();
}

static void execlists_reset_finish(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;

        /*
         * After a GPU reset, we may have requests to replay. Do so now while
         * we still have the forcewake to be sure that the GPU is not allowed
         * to sleep before we restart and reload a context.
         *
         * If the GPU reset fails, the engine may still be alive with requests
         * inflight. We expect those to complete, or for the device to be
         * reset as the next level of recovery, and as a final resort we
         * will declare the device wedged.
         */
        GEM_BUG_ON(!reset_in_progress(engine));

        /* And kick in case we missed a new request submission. */
        if (__tasklet_enable(&engine->sched_engine->tasklet))
                __execlists_kick(execlists);

        ENGINE_TRACE(engine, "depth->%d\n",
                     atomic_read(&engine->sched_engine->tasklet.count));
}

static void gen8_logical_ring_enable_irq(struct intel_engine_cs *engine)
{
        ENGINE_WRITE(engine, RING_IMR,
                     ~(engine->irq_enable_mask | engine->irq_keep_mask));
        ENGINE_POSTING_READ(engine, RING_IMR);
}

static void gen8_logical_ring_disable_irq(struct intel_engine_cs *engine)
{
        ENGINE_WRITE(engine, RING_IMR, ~engine->irq_keep_mask);
}

static void execlists_park(struct intel_engine_cs *engine)
{
        cancel_timer(&engine->execlists.timer);
        cancel_timer(&engine->execlists.preempt);
}

static void add_to_engine(struct i915_request *rq)
{
        lockdep_assert_held(&rq->engine->sched_engine->lock);
        list_move_tail(&rq->sched.link, &rq->engine->sched_engine->requests);
}

static void remove_from_engine(struct i915_request *rq)
{
        struct intel_engine_cs *engine, *locked;

        /*
         * Virtual engines complicate acquiring the engine timeline lock,
         * as their rq->engine pointer is not stable until under that
         * engine lock. The simple ploy we use is to take the lock then
         * check that the rq still belongs to the newly locked engine.
         */
        locked = READ_ONCE(rq->engine);
        spin_lock_irq(&locked->sched_engine->lock);
        while (unlikely(locked != (engine = READ_ONCE(rq->engine)))) {
                spin_unlock(&locked->sched_engine->lock);
                spin_lock(&engine->sched_engine->lock);
                locked = engine;
        }
        list_del_init(&rq->sched.link);

        clear_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
        clear_bit(I915_FENCE_FLAG_HOLD, &rq->fence.flags);

        /* Prevent further __await_execution() registering a cb, then flush */
        set_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags);

        spin_unlock_irq(&locked->sched_engine->lock);

        i915_request_notify_execute_cb_imm(rq);
}

static bool can_preempt(struct intel_engine_cs *engine)
{
        if (GRAPHICS_VER(engine->i915) > 8)
                return true;

        /* GPGPU on bdw requires extra w/a; not implemented */
        return engine->class != RENDER_CLASS;
}

static void kick_execlists(const struct i915_request *rq, int prio)
{
        struct intel_engine_cs *engine = rq->engine;
        struct i915_sched_engine *sched_engine = engine->sched_engine;
        const struct i915_request *inflight;

        /*
         * We only need to kick the tasklet once for the high priority
         * new context we add into the queue.
         */
        if (prio <= sched_engine->queue_priority_hint)
                return;

        rcu_read_lock();

        /* Nothing currently active? We're overdue for a submission! */
        inflight = execlists_active(&engine->execlists);
        if (!inflight)
                goto unlock;

        /*
         * If we are already the currently executing context, don't
         * bother evaluating if we should preempt ourselves.
         */
        if (inflight->context == rq->context)
                goto unlock;

        ENGINE_TRACE(engine,
                     "bumping queue-priority-hint:%d for rq:%llx:%lld, inflight:%llx:%lld prio %d\n",
                     prio,
                     rq->fence.context, rq->fence.seqno,
                     inflight->fence.context, inflight->fence.seqno,
                     inflight->sched.attr.priority);

        sched_engine->queue_priority_hint = prio;

        /*
         * Allow preemption of low -> normal -> high, but we do
         * not allow low priority tasks to preempt other low priority
         * tasks under the impression that latency for low priority
         * tasks does not matter (as much as background throughput),
         * so kiss.
         */
        if (prio >= max(I915_PRIORITY_NORMAL, rq_prio(inflight)))
                tasklet_hi_schedule(&sched_engine->tasklet);

unlock:
        rcu_read_unlock();
}

static void execlists_set_default_submission(struct intel_engine_cs *engine)
{
        engine->submit_request = execlists_submit_request;
        engine->sched_engine->schedule = i915_schedule;
        engine->sched_engine->kick_backend = kick_execlists;
        engine->sched_engine->tasklet.callback = execlists_submission_tasklet;
}

static void execlists_shutdown(struct intel_engine_cs *engine)
{
        /* Synchronise with residual timers and any softirq they raise */
        del_timer_sync(&engine->execlists.timer);
        del_timer_sync(&engine->execlists.preempt);
        tasklet_kill(&engine->sched_engine->tasklet);
}

static void execlists_release(struct intel_engine_cs *engine)
{
        engine->sanitize = NULL; /* no longer in control, nothing to sanitize */

        execlists_shutdown(engine);

        intel_engine_cleanup_common(engine);
        lrc_fini_wa_ctx(engine);
}

static ktime_t __execlists_engine_busyness(struct intel_engine_cs *engine,
                                           ktime_t *now)
{
        struct intel_engine_execlists_stats *stats = &engine->stats.execlists;
        ktime_t total = stats->total;

        /*
         * If the engine is executing something at the moment
         * add it to the total.
         */
        *now = ktime_get();
        if (READ_ONCE(stats->active))
                total = ktime_add(total, ktime_sub(*now, stats->start));

        return total;
}

static ktime_t execlists_engine_busyness(struct intel_engine_cs *engine,
                                         ktime_t *now)
{
        struct intel_engine_execlists_stats *stats = &engine->stats.execlists;
        unsigned int seq;
        ktime_t total;

        do {
                seq = read_seqcount_begin(&stats->lock);
                total = __execlists_engine_busyness(engine, now);
        } while (read_seqcount_retry(&stats->lock, seq));

        return total;
}

static void
logical_ring_default_vfuncs(struct intel_engine_cs *engine)
{
        /* Default vfuncs which can be overridden by each engine. */

        engine->resume = execlists_resume;

        engine->cops = &execlists_context_ops;
        engine->request_alloc = execlists_request_alloc;
        engine->add_active_request = add_to_engine;
        engine->remove_active_request = remove_from_engine;

        engine->reset.prepare = execlists_reset_prepare;
        engine->reset.rewind = execlists_reset_rewind;
        engine->reset.cancel = execlists_reset_cancel;
        engine->reset.finish = execlists_reset_finish;

        engine->park = execlists_park;
        engine->unpark = NULL;

        engine->emit_flush = gen8_emit_flush_xcs;
        engine->emit_init_breadcrumb = gen8_emit_init_breadcrumb;
        engine->emit_fini_breadcrumb = gen8_emit_fini_breadcrumb_xcs;
        if (GRAPHICS_VER(engine->i915) >= 12) {
                engine->emit_fini_breadcrumb = gen12_emit_fini_breadcrumb_xcs;
                engine->emit_flush = gen12_emit_flush_xcs;
        }
        engine->set_default_submission = execlists_set_default_submission;

        if (GRAPHICS_VER(engine->i915) < 11) {
                engine->irq_enable = gen8_logical_ring_enable_irq;
                engine->irq_disable = gen8_logical_ring_disable_irq;
        } else {
                /*
                 * TODO: On Gen11 interrupt masks need to be clear
                 * to allow C6 entry. Keep interrupts enabled at
                 * and take the hit of generating extra interrupts
                 * until a more refined solution exists.
                 */
        }
        intel_engine_set_irq_handler(engine, execlists_irq_handler);

        engine->flags |= I915_ENGINE_SUPPORTS_STATS;
        if (!intel_vgpu_active(engine->i915)) {
                engine->flags |= I915_ENGINE_HAS_SEMAPHORES;
                if (can_preempt(engine)) {
                        engine->flags |= I915_ENGINE_HAS_PREEMPTION;
                        if (CONFIG_DRM_I915_TIMESLICE_DURATION)
                                engine->flags |= I915_ENGINE_HAS_TIMESLICES;
                }
        }

        if (intel_engine_has_preemption(engine))
                engine->emit_bb_start = gen8_emit_bb_start;
        else
                engine->emit_bb_start = gen8_emit_bb_start_noarb;

        engine->busyness = execlists_engine_busyness;
}

static void logical_ring_default_irqs(struct intel_engine_cs *engine)
{
        unsigned int shift = 0;

        if (GRAPHICS_VER(engine->i915) < 11) {
                const u8 irq_shifts[] = {
                        [RCS0]  = GEN8_RCS_IRQ_SHIFT,
                        [BCS0]  = GEN8_BCS_IRQ_SHIFT,
                        [VCS0]  = GEN8_VCS0_IRQ_SHIFT,
                        [VCS1]  = GEN8_VCS1_IRQ_SHIFT,
                        [VECS0] = GEN8_VECS_IRQ_SHIFT,
                };

                shift = irq_shifts[engine->id];
        }

        engine->irq_enable_mask = GT_RENDER_USER_INTERRUPT << shift;
        engine->irq_keep_mask = GT_CONTEXT_SWITCH_INTERRUPT << shift;
        engine->irq_keep_mask |= GT_CS_MASTER_ERROR_INTERRUPT << shift;
        engine->irq_keep_mask |= GT_WAIT_SEMAPHORE_INTERRUPT << shift;
}

static void rcs_submission_override(struct intel_engine_cs *engine)
{
        switch (GRAPHICS_VER(engine->i915)) {
        case 12:
                engine->emit_flush = gen12_emit_flush_rcs;
                engine->emit_fini_breadcrumb = gen12_emit_fini_breadcrumb_rcs;
                break;
        case 11:
                engine->emit_flush = gen11_emit_flush_rcs;
                engine->emit_fini_breadcrumb = gen11_emit_fini_breadcrumb_rcs;
                break;
        default:
                engine->emit_flush = gen8_emit_flush_rcs;
                engine->emit_fini_breadcrumb = gen8_emit_fini_breadcrumb_rcs;
                break;
        }
}

int intel_execlists_submission_setup(struct intel_engine_cs *engine)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct drm_i915_private *i915 = engine->i915;
        struct intel_uncore *uncore = engine->uncore;
        u32 base = engine->mmio_base;

        tasklet_setup(&engine->sched_engine->tasklet, execlists_submission_tasklet);
        timer_setup(&engine->execlists.timer, execlists_timeslice, 0);
        timer_setup(&engine->execlists.preempt, execlists_preempt, 0);

        logical_ring_default_vfuncs(engine);
        logical_ring_default_irqs(engine);

        if (engine->flags & I915_ENGINE_HAS_RCS_REG_STATE)
                rcs_submission_override(engine);

        lrc_init_wa_ctx(engine);

        if (HAS_LOGICAL_RING_ELSQ(i915)) {
                execlists->submit_reg = uncore->regs +
                        i915_mmio_reg_offset(RING_EXECLIST_SQ_CONTENTS(base));
                execlists->ctrl_reg = uncore->regs +
                        i915_mmio_reg_offset(RING_EXECLIST_CONTROL(base));

                engine->fw_domain = intel_uncore_forcewake_for_reg(engine->uncore,
                                    RING_EXECLIST_CONTROL(engine->mmio_base),
                                    FW_REG_WRITE);
        } else {
                execlists->submit_reg = uncore->regs +
                        i915_mmio_reg_offset(RING_ELSP(base));
        }

        execlists->csb_status =
                (u64 *)&engine->status_page.addr[I915_HWS_CSB_BUF0_INDEX];

        execlists->csb_write =
                &engine->status_page.addr[INTEL_HWS_CSB_WRITE_INDEX(i915)];

        if (GRAPHICS_VER(i915) < 11)
                execlists->csb_size = GEN8_CSB_ENTRIES;
        else
                execlists->csb_size = GEN11_CSB_ENTRIES;

        engine->context_tag = GENMASK(BITS_PER_LONG - 2, 0);
        if (GRAPHICS_VER(engine->i915) >= 11 &&
            GRAPHICS_VER_FULL(engine->i915) < IP_VER(12, 50)) {
                execlists->ccid |= engine->instance << (GEN11_ENGINE_INSTANCE_SHIFT - 32);
                execlists->ccid |= engine->class << (GEN11_ENGINE_CLASS_SHIFT - 32);
        }

        /* Finally, take ownership and responsibility for cleanup! */
        engine->sanitize = execlists_sanitize;
        engine->release = execlists_release;

        return 0;
}

static struct list_head *virtual_queue(struct virtual_engine *ve)
{
        return &ve->base.sched_engine->default_priolist.requests;
}

static void rcu_virtual_context_destroy(struct work_struct *wrk)
{
        struct virtual_engine *ve =
                container_of(wrk, typeof(*ve), rcu.work);
        unsigned int n;

        GEM_BUG_ON(ve->context.inflight);

        /* Preempt-to-busy may leave a stale request behind. */
        if (unlikely(ve->request)) {
                struct i915_request *old;

                spin_lock_irq(&ve->base.sched_engine->lock);

                old = fetch_and_zero(&ve->request);
                if (old) {
                        GEM_BUG_ON(!__i915_request_is_complete(old));
                        __i915_request_submit(old);
                        i915_request_put(old);
                }

                spin_unlock_irq(&ve->base.sched_engine->lock);
        }

        /*
         * Flush the tasklet in case it is still running on another core.
         *
         * This needs to be done before we remove ourselves from the siblings'
         * rbtrees as in the case it is running in parallel, it may reinsert
         * the rb_node into a sibling.
         */
        tasklet_kill(&ve->base.sched_engine->tasklet);

        /* Decouple ourselves from the siblings, no more access allowed. */
        for (n = 0; n < ve->num_siblings; n++) {
                struct intel_engine_cs *sibling = ve->siblings[n];
                struct rb_node *node = &ve->nodes[sibling->id].rb;

                if (RB_EMPTY_NODE(node))
                        continue;

                spin_lock_irq(&sibling->sched_engine->lock);

                /* Detachment is lazily performed in the sched_engine->tasklet */
                if (!RB_EMPTY_NODE(node))
                        rb_erase_cached(node, &sibling->execlists.virtual);

                spin_unlock_irq(&sibling->sched_engine->lock);
        }
        GEM_BUG_ON(__tasklet_is_scheduled(&ve->base.sched_engine->tasklet));
        GEM_BUG_ON(!list_empty(virtual_queue(ve)));

        lrc_fini(&ve->context);
        intel_context_fini(&ve->context);

        if (ve->base.breadcrumbs)
                intel_breadcrumbs_put(ve->base.breadcrumbs);
        if (ve->base.sched_engine)
                i915_sched_engine_put(ve->base.sched_engine);
        intel_engine_free_request_pool(&ve->base);

        kfree(ve);
}

static void virtual_context_destroy(struct kref *kref)
{
        struct virtual_engine *ve =
                container_of(kref, typeof(*ve), context.ref);

        GEM_BUG_ON(!list_empty(&ve->context.signals));

        /*
         * When destroying the virtual engine, we have to be aware that
         * it may still be in use from an hardirq/softirq context causing
         * the resubmission of a completed request (background completion
         * due to preempt-to-busy). Before we can free the engine, we need
         * to flush the submission code and tasklets that are still potentially
         * accessing the engine. Flushing the tasklets requires process context,
         * and since we can guard the resubmit onto the engine with an RCU read
         * lock, we can delegate the free of the engine to an RCU worker.
         */
        INIT_RCU_WORK(&ve->rcu, rcu_virtual_context_destroy);
        queue_rcu_work(system_wq, &ve->rcu);
}

static void virtual_engine_initial_hint(struct virtual_engine *ve)
{
        int swp;

        /*
         * Pick a random sibling on starting to help spread the load around.
         *
         * New contexts are typically created with exactly the same order
         * of siblings, and often started in batches. Due to the way we iterate
         * the array of sibling when submitting requests, sibling[0] is
         * prioritised for dequeuing. If we make sure that sibling[0] is fairly
         * randomised across the system, we also help spread the load by the
         * first engine we inspect being different each time.
         *
         * NB This does not force us to execute on this engine, it will just
         * typically be the first we inspect for submission.
         */
        swp = prandom_u32_max(ve->num_siblings);
        if (swp)
                swap(ve->siblings[swp], ve->siblings[0]);
}

static int virtual_context_alloc(struct intel_context *ce)
{
        struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

        return lrc_alloc(ce, ve->siblings[0]);
}

static int virtual_context_pre_pin(struct intel_context *ce,
                                   struct i915_gem_ww_ctx *ww,
                                   void **vaddr)
{
        struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

         /* Note: we must use a real engine class for setting up reg state */
        return __execlists_context_pre_pin(ce, ve->siblings[0], ww, vaddr);
}

static int virtual_context_pin(struct intel_context *ce, void *vaddr)
{
        struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

        return lrc_pin(ce, ve->siblings[0], vaddr);
}

static void virtual_context_enter(struct intel_context *ce)
{
        struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
        unsigned int n;

        for (n = 0; n < ve->num_siblings; n++)
                intel_engine_pm_get(ve->siblings[n]);

        intel_timeline_enter(ce->timeline);
}

static void virtual_context_exit(struct intel_context *ce)
{
        struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
        unsigned int n;

        intel_timeline_exit(ce->timeline);

        for (n = 0; n < ve->num_siblings; n++)
                intel_engine_pm_put(ve->siblings[n]);
}

static struct intel_engine_cs *
virtual_get_sibling(struct intel_engine_cs *engine, unsigned int sibling)
{
        struct virtual_engine *ve = to_virtual_engine(engine);

        if (sibling >= ve->num_siblings)
                return NULL;

        return ve->siblings[sibling];
}

static const struct intel_context_ops virtual_context_ops = {
        .flags = COPS_HAS_INFLIGHT,

        .alloc = virtual_context_alloc,

        .cancel_request = execlists_context_cancel_request,

        .pre_pin = virtual_context_pre_pin,
        .pin = virtual_context_pin,
        .unpin = lrc_unpin,
        .post_unpin = lrc_post_unpin,

        .enter = virtual_context_enter,
        .exit = virtual_context_exit,

        .destroy = virtual_context_destroy,

        .get_sibling = virtual_get_sibling,
};

static intel_engine_mask_t virtual_submission_mask(struct virtual_engine *ve)
{
        struct i915_request *rq;
        intel_engine_mask_t mask;

        rq = READ_ONCE(ve->request);
        if (!rq)
                return 0;

        /* The rq is ready for submission; rq->execution_mask is now stable. */
        mask = rq->execution_mask;
        if (unlikely(!mask)) {
                /* Invalid selection, submit to a random engine in error */
                i915_request_set_error_once(rq, -ENODEV);
                mask = ve->siblings[0]->mask;
        }

        ENGINE_TRACE(&ve->base, "rq=%llx:%lld, mask=%x, prio=%d\n",
                     rq->fence.context, rq->fence.seqno,
                     mask, ve->base.sched_engine->queue_priority_hint);

        return mask;
}

static void virtual_submission_tasklet(struct tasklet_struct *t)
{
        struct i915_sched_engine *sched_engine =
                from_tasklet(sched_engine, t, tasklet);
        struct virtual_engine * const ve =
                (struct virtual_engine *)sched_engine->private_data;
        const int prio = READ_ONCE(sched_engine->queue_priority_hint);
        intel_engine_mask_t mask;
        unsigned int n;

        rcu_read_lock();
        mask = virtual_submission_mask(ve);
        rcu_read_unlock();
        if (unlikely(!mask))
                return;

        for (n = 0; n < ve->num_siblings; n++) {
                struct intel_engine_cs *sibling = READ_ONCE(ve->siblings[n]);
                struct ve_node * const node = &ve->nodes[sibling->id];
                struct rb_node **parent, *rb;
                bool first;

                if (!READ_ONCE(ve->request))
                        break; /* already handled by a sibling's tasklet */

                spin_lock_irq(&sibling->sched_engine->lock);

                if (unlikely(!(mask & sibling->mask))) {
                        if (!RB_EMPTY_NODE(&node->rb)) {
                                rb_erase_cached(&node->rb,
                                                &sibling->execlists.virtual);
                                RB_CLEAR_NODE(&node->rb);
                        }

                        goto unlock_engine;
                }

                if (unlikely(!RB_EMPTY_NODE(&node->rb))) {
                        /*
                         * Cheat and avoid rebalancing the tree if we can
                         * reuse this node in situ.
                         */
                        first = rb_first_cached(&sibling->execlists.virtual) ==
                                &node->rb;
                        if (prio == node->prio || (prio > node->prio && first))
                                goto submit_engine;

                        rb_erase_cached(&node->rb, &sibling->execlists.virtual);
                }

                rb = NULL;
                first = true;
                parent = &sibling->execlists.virtual.rb_root.rb_node;
                while (*parent) {
                        struct ve_node *other;

                        rb = *parent;
                        other = rb_entry(rb, typeof(*other), rb);
                        if (prio > other->prio) {
                                parent = &rb->rb_left;
                        } else {
                                parent = &rb->rb_right;
                                first = false;
                        }
                }

                rb_link_node(&node->rb, rb, parent);
                rb_insert_color_cached(&node->rb,
                                       &sibling->execlists.virtual,
                                       first);

submit_engine:
                GEM_BUG_ON(RB_EMPTY_NODE(&node->rb));
                node->prio = prio;
                if (first && prio > sibling->sched_engine->queue_priority_hint)
                        tasklet_hi_schedule(&sibling->sched_engine->tasklet);

unlock_engine:
                spin_unlock_irq(&sibling->sched_engine->lock);

                if (intel_context_inflight(&ve->context))
                        break;
        }
}

static void virtual_submit_request(struct i915_request *rq)
{
        struct virtual_engine *ve = to_virtual_engine(rq->engine);
        unsigned long flags;

        ENGINE_TRACE(&ve->base, "rq=%llx:%lld\n",
                     rq->fence.context,
                     rq->fence.seqno);

        GEM_BUG_ON(ve->base.submit_request != virtual_submit_request);

        spin_lock_irqsave(&ve->base.sched_engine->lock, flags);

        /* By the time we resubmit a request, it may be completed */
        if (__i915_request_is_complete(rq)) {
                __i915_request_submit(rq);
                goto unlock;
        }

        if (ve->request) { /* background completion from preempt-to-busy */
                GEM_BUG_ON(!__i915_request_is_complete(ve->request));
                __i915_request_submit(ve->request);
                i915_request_put(ve->request);
        }

        ve->base.sched_engine->queue_priority_hint = rq_prio(rq);
        ve->request = i915_request_get(rq);

        GEM_BUG_ON(!list_empty(virtual_queue(ve)));
        list_move_tail(&rq->sched.link, virtual_queue(ve));

        tasklet_hi_schedule(&ve->base.sched_engine->tasklet);

unlock:
        spin_unlock_irqrestore(&ve->base.sched_engine->lock, flags);
}

static struct intel_context *
execlists_create_virtual(struct intel_engine_cs **siblings, unsigned int count,
                         unsigned long flags)
{
        struct virtual_engine *ve;
        unsigned int n;
        int err;

        ve = kzalloc(struct_size(ve, siblings, count), GFP_KERNEL);
        if (!ve)
                return ERR_PTR(-ENOMEM);

        ve->base.i915 = siblings[0]->i915;
        ve->base.gt = siblings[0]->gt;
        ve->base.uncore = siblings[0]->uncore;
        ve->base.id = -1;

        ve->base.class = OTHER_CLASS;
        ve->base.uabi_class = I915_ENGINE_CLASS_INVALID;
        ve->base.instance = I915_ENGINE_CLASS_INVALID_VIRTUAL;
        ve->base.uabi_instance = I915_ENGINE_CLASS_INVALID_VIRTUAL;

        /*
         * The decision on whether to submit a request using semaphores
         * depends on the saturated state of the engine. We only compute
         * this during HW submission of the request, and we need for this
         * state to be globally applied to all requests being submitted
         * to this engine. Virtual engines encompass more than one physical
         * engine and so we cannot accurately tell in advance if one of those
         * engines is already saturated and so cannot afford to use a semaphore
         * and be pessimized in priority for doing so -- if we are the only
         * context using semaphores after all other clients have stopped, we
         * will be starved on the saturated system. Such a global switch for
         * semaphores is less than ideal, but alas is the current compromise.
         */
        ve->base.saturated = ALL_ENGINES;

        snprintf(ve->base.name, sizeof(ve->base.name), "virtual");

        intel_engine_init_execlists(&ve->base);

        ve->base.sched_engine = i915_sched_engine_create(ENGINE_VIRTUAL);
        if (!ve->base.sched_engine) {
                err = -ENOMEM;
                goto err_put;
        }
        ve->base.sched_engine->private_data = &ve->base;

        ve->base.cops = &virtual_context_ops;
        ve->base.request_alloc = execlists_request_alloc;

        ve->base.sched_engine->schedule = i915_schedule;
        ve->base.sched_engine->kick_backend = kick_execlists;
        ve->base.submit_request = virtual_submit_request;

        INIT_LIST_HEAD(virtual_queue(ve));
        tasklet_setup(&ve->base.sched_engine->tasklet, virtual_submission_tasklet);

        intel_context_init(&ve->context, &ve->base);

        ve->base.breadcrumbs = intel_breadcrumbs_create(NULL);
        if (!ve->base.breadcrumbs) {
                err = -ENOMEM;
                goto err_put;
        }

        for (n = 0; n < count; n++) {
                struct intel_engine_cs *sibling = siblings[n];

                GEM_BUG_ON(!is_power_of_2(sibling->mask));
                if (sibling->mask & ve->base.mask) {
                        DRM_DEBUG("duplicate %s entry in load balancer\n",
                                  sibling->name);
                        err = -EINVAL;
                        goto err_put;
                }

                /*
                 * The virtual engine implementation is tightly coupled to
                 * the execlists backend -- we push out request directly
                 * into a tree inside each physical engine. We could support
                 * layering if we handle cloning of the requests and
                 * submitting a copy into each backend.
                 */
                if (sibling->sched_engine->tasklet.callback !=
                    execlists_submission_tasklet) {
                        err = -ENODEV;
                        goto err_put;
                }

                GEM_BUG_ON(RB_EMPTY_NODE(&ve->nodes[sibling->id].rb));
                RB_CLEAR_NODE(&ve->nodes[sibling->id].rb);

                ve->siblings[ve->num_siblings++] = sibling;
                ve->base.mask |= sibling->mask;
                ve->base.logical_mask |= sibling->logical_mask;

                /*
                 * All physical engines must be compatible for their emission
                 * functions (as we build the instructions during request
                 * construction and do not alter them before submission
                 * on the physical engine). We use the engine class as a guide
                 * here, although that could be refined.
                 */
                if (ve->base.class != OTHER_CLASS) {
                        if (ve->base.class != sibling->class) {
                                DRM_DEBUG("invalid mixing of engine class, sibling %d, already %d\n",
                                          sibling->class, ve->base.class);
                                err = -EINVAL;
                                goto err_put;
                        }
                        continue;
                }

                ve->base.class = sibling->class;
                ve->base.uabi_class = sibling->uabi_class;
                snprintf(ve->base.name, sizeof(ve->base.name),
                         "v%dx%d", ve->base.class, count);
                ve->base.context_size = sibling->context_size;

                ve->base.add_active_request = sibling->add_active_request;
                ve->base.remove_active_request = sibling->remove_active_request;
                ve->base.emit_bb_start = sibling->emit_bb_start;
                ve->base.emit_flush = sibling->emit_flush;
                ve->base.emit_init_breadcrumb = sibling->emit_init_breadcrumb;
                ve->base.emit_fini_breadcrumb = sibling->emit_fini_breadcrumb;
                ve->base.emit_fini_breadcrumb_dw =
                        sibling->emit_fini_breadcrumb_dw;

                ve->base.flags = sibling->flags;
        }

        ve->base.flags |= I915_ENGINE_IS_VIRTUAL;

        virtual_engine_initial_hint(ve);
        return &ve->context;

err_put:
        intel_context_put(&ve->context);
        return ERR_PTR(err);
}

void intel_execlists_show_requests(struct intel_engine_cs *engine,
                                   struct drm_printer *m,
                                   void (*show_request)(struct drm_printer *m,
                                                        const struct i915_request *rq,
                                                        const char *prefix,
                                                        int indent),
                                   unsigned int max)
{
        const struct intel_engine_execlists *execlists = &engine->execlists;
        struct i915_sched_engine *sched_engine = engine->sched_engine;
        struct i915_request *rq, *last;
        unsigned long flags;
        unsigned int count;
        struct rb_node *rb;

        spin_lock_irqsave(&sched_engine->lock, flags);

        last = NULL;
        count = 0;
        list_for_each_entry(rq, &sched_engine->requests, sched.link) {
                if (count++ < max - 1)
                        show_request(m, rq, "\t\t", 0);
                else
                        last = rq;
        }
        if (last) {
                if (count > max) {
                        drm_printf(m,
                                   "\t\t...skipping %d executing requests...\n",
                                   count - max);
                }
                show_request(m, last, "\t\t", 0);
        }

        if (sched_engine->queue_priority_hint != INT_MIN)
                drm_printf(m, "\t\tQueue priority hint: %d\n",
                           READ_ONCE(sched_engine->queue_priority_hint));

        last = NULL;
        count = 0;
        for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
                struct i915_priolist *p = rb_entry(rb, typeof(*p), node);

                priolist_for_each_request(rq, p) {
                        if (count++ < max - 1)
                                show_request(m, rq, "\t\t", 0);
                        else
                                last = rq;
                }
        }
        if (last) {
                if (count > max) {
                        drm_printf(m,
                                   "\t\t...skipping %d queued requests...\n",
                                   count - max);
                }
                show_request(m, last, "\t\t", 0);
        }

        last = NULL;
        count = 0;
        for (rb = rb_first_cached(&execlists->virtual); rb; rb = rb_next(rb)) {
                struct virtual_engine *ve =
                        rb_entry(rb, typeof(*ve), nodes[engine->id].rb);
                struct i915_request *rq = READ_ONCE(ve->request);

                if (rq) {
                        if (count++ < max - 1)
                                show_request(m, rq, "\t\t", 0);
                        else
                                last = rq;
                }
        }
        if (last) {
                if (count > max) {
                        drm_printf(m,
                                   "\t\t...skipping %d virtual requests...\n",
                                   count - max);
                }
                show_request(m, last, "\t\t", 0);
        }

        spin_unlock_irqrestore(&sched_engine->lock, flags);
}

#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftest_execlists.c"
#endif