drm/i915/guc: Fill preempt context once at init time

Since we're inhibiting context save of preempt context, we're no longer
tracking the position of HEAD/TAIL. With GuC, we're adding a new
breadcrumb for each preemption, which means that the HW will do more and
more breadcrumb writes. Eventually the ring is filled, and we're
submitting the preemption context with HEAD==TAIL==0, which won't result
in breadcrumb write, but will trigger hangcheck instead.
Instead of writing a new preempt breadcrumb for each preemption, let's
just fill the ring once at init time (which also saves a couple of
instructions in the tasklet).

v2: Assert that context save restore is inhibited, don't assert on ring
    alignment. (Chris)
v3: Cleanup checkpatch.

Fixes: 517aaffe0c1b ("drm/i915/execlists: Inhibit context save/restore for the fake preempt context")
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180226163800.21745-1-michal.winiarski@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
index 586dde579903ae4083ede1a689f93c4a794edf2d..8a8ad2fe158d7527bd5134a49d6366808bee11a2 100644 (file)
--- a/drivers/gpu/drm/i915/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/intel_guc_submission.c
@@ -26,8 +26,14 @@
 #include <trace/events/dma_fence.h>
 
 #include "intel_guc_submission.h"
+#include "intel_lrc_reg.h"
 #include "i915_drv.h"
 
+#define GUC_PREEMPT_FINISHED           0x1
+#define GUC_PREEMPT_BREADCRUMB_DWORDS  0x8
+#define GUC_PREEMPT_BREADCRUMB_BYTES   \
+       (sizeof(u32) * GUC_PREEMPT_BREADCRUMB_DWORDS)
+
 /**
  * DOC: GuC-based command submission
  *
@@ -535,8 +541,6 @@ static void flush_ggtt_writes(struct i915_vma *vma)
                POSTING_READ_FW(GUC_STATUS);
 }
 
-#define GUC_PREEMPT_FINISHED 0x1
-#define GUC_PREEMPT_BREADCRUMB_DWORDS 0x8
 static void inject_preempt_context(struct work_struct *work)
 {
        struct guc_preempt_work *preempt_work =
@@ -546,37 +550,17 @@ static void inject_preempt_context(struct work_struct *work)
                                             preempt_work[engine->id]);
        struct intel_guc_client *client = guc->preempt_client;
        struct guc_stage_desc *stage_desc = __get_stage_desc(client);
-       struct intel_ring *ring = client->owner->engine[engine->id].ring;
        u32 ctx_desc = lower_32_bits(intel_lr_context_descriptor(client->owner,
                                                                 engine));
-       u32 *cs = ring->vaddr + ring->tail;
        u32 data[7];
 
-       if (engine->id == RCS) {
-               cs = gen8_emit_ggtt_write_rcs(cs, GUC_PREEMPT_FINISHED,
-                               intel_hws_preempt_done_address(engine));
-       } else {
-               cs = gen8_emit_ggtt_write(cs, GUC_PREEMPT_FINISHED,
-                               intel_hws_preempt_done_address(engine));
-               *cs++ = MI_NOOP;
-               *cs++ = MI_NOOP;
-       }
-       *cs++ = MI_USER_INTERRUPT;
-       *cs++ = MI_NOOP;
-
-       GEM_BUG_ON(!IS_ALIGNED(ring->size,
-                              GUC_PREEMPT_BREADCRUMB_DWORDS * sizeof(u32)));
-       GEM_BUG_ON((void *)cs - (ring->vaddr + ring->tail) !=
-                  GUC_PREEMPT_BREADCRUMB_DWORDS * sizeof(u32));
-
-       ring->tail += GUC_PREEMPT_BREADCRUMB_DWORDS * sizeof(u32);
-       ring->tail &= (ring->size - 1);
-
-       flush_ggtt_writes(ring->vma);
-
+       /*
+        * The ring contains commands to write GUC_PREEMPT_FINISHED into HWSP.
+        * See guc_fill_preempt_context().
+        */
        spin_lock_irq(&client->wq_lock);
        guc_wq_item_append(client, engine->guc_id, ctx_desc,
-                          ring->tail / sizeof(u64), 0);
+                          GUC_PREEMPT_BREADCRUMB_BYTES / sizeof(u64), 0);
        spin_unlock_irq(&client->wq_lock);
 
        /*
@@ -972,6 +956,62 @@ static void guc_client_free(struct intel_guc_client *client)
        kfree(client);
 }
 
+static inline bool ctx_save_restore_disabled(struct intel_context *ce)
+{
+       u32 sr = ce->lrc_reg_state[CTX_CONTEXT_CONTROL + 1];
+
+#define SR_DISABLED \
+       _MASKED_BIT_ENABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT | \
+                          CTX_CTRL_ENGINE_CTX_SAVE_INHIBIT)
+
+       return (sr & SR_DISABLED) == SR_DISABLED;
+
+#undef SR_DISABLED
+}
+
+static void guc_fill_preempt_context(struct intel_guc *guc)
+{
+       struct drm_i915_private *dev_priv = guc_to_i915(guc);
+       struct intel_guc_client *client = guc->preempt_client;
+       struct intel_engine_cs *engine;
+       enum intel_engine_id id;
+
+       for_each_engine(engine, dev_priv, id) {
+               struct intel_context *ce = &client->owner->engine[id];
+               u32 addr = intel_hws_preempt_done_address(engine);
+               u32 *cs;
+
+               GEM_BUG_ON(!ce->pin_count);
+
+               /*
+                * We rely on this context image *not* being saved after
+                * preemption. This ensures that the RING_HEAD / RING_TAIL
+                * remain pointing at initial values forever.
+                */
+               GEM_BUG_ON(!ctx_save_restore_disabled(ce));
+
+               cs = ce->ring->vaddr;
+               if (id == RCS) {
+                       cs = gen8_emit_ggtt_write_rcs(cs,
+                                                     GUC_PREEMPT_FINISHED,
+                                                     addr);
+               } else {
+                       cs = gen8_emit_ggtt_write(cs,
+                                                 GUC_PREEMPT_FINISHED,
+                                                 addr);
+                       *cs++ = MI_NOOP;
+                       *cs++ = MI_NOOP;
+               }
+               *cs++ = MI_USER_INTERRUPT;
+               *cs++ = MI_NOOP;
+
+               GEM_BUG_ON((void *)cs - ce->ring->vaddr !=
+                          GUC_PREEMPT_BREADCRUMB_BYTES);
+
+               flush_ggtt_writes(ce->ring->vma);
+       }
+}
+
 static int guc_clients_create(struct intel_guc *guc)
 {
        struct drm_i915_private *dev_priv = guc_to_i915(guc);
@@ -1002,6 +1042,8 @@ static int guc_clients_create(struct intel_guc *guc)
                        return PTR_ERR(client);
                }
                guc->preempt_client = client;
+
+               guc_fill_preempt_context(guc);
        }
 
        return 0;