iommu/arm-smmu-v3: Increase CMDQ drain timeout value

Waiting for a CMD_SYNC to be processed involves waiting for the command
queue to drain, which can take an awful lot longer than waiting for a
single entry to become available. Consequently, the common timeout value
of 100us has been observed to be too short on some platforms when a
CMD_SYNC is issued into a queued full of TLBI commands.

This patch resolves the issue by using a different (1s) timeout when
waiting for the CMDQ to drain and using a simple back-off mechanism
when polling the cons pointer in the absence of WFE support.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
[will: rewrote commit message and cosmetic changes]
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 380969aa60d5a6070765d4eaae3532c1b3324a8c..6a06be7626dbebfa61662a42da835b1f6bee93e4 100644 (file)
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -408,6 +408,7 @@
 
 /* High-level queue structures */
 #define ARM_SMMU_POLL_TIMEOUT_US       100
+#define ARM_SMMU_CMDQ_DRAIN_TIMEOUT_US 1000000 /* 1s! */
 
 #define MSI_IOVA_BASE                  0x8000000
 #define MSI_IOVA_LENGTH                        0x100000
@@ -737,7 +738,13 @@ static void queue_inc_prod(struct arm_smmu_queue *q)
  */
 static int queue_poll_cons(struct arm_smmu_queue *q, bool drain, bool wfe)
 {
-       ktime_t timeout = ktime_add_us(ktime_get(), ARM_SMMU_POLL_TIMEOUT_US);
+       ktime_t timeout;
+       unsigned int delay = 1;
+
+       /* Wait longer if it's queue drain */
+       timeout = ktime_add_us(ktime_get(), drain ?
+                                           ARM_SMMU_CMDQ_DRAIN_TIMEOUT_US :
+                                           ARM_SMMU_POLL_TIMEOUT_US);
 
        while (queue_sync_cons(q), (drain ? !queue_empty(q) : queue_full(q))) {
                if (ktime_compare(ktime_get(), timeout) > 0)
@@ -747,7 +754,8 @@ static int queue_poll_cons(struct arm_smmu_queue *q, bool drain, bool wfe)
                        wfe();
                } else {
                        cpu_relax();
-                       udelay(1);
+                       udelay(delay);
+                       delay *= 2;
                }
        }