From: Christian König <christian.koenig@amd.com>
Date: Fri, 11 Mar 2016 16:49:58 +0000 (+0100)
Subject: drm/amdgpu: cleanup amdgpu_fence_activity
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=d9713ef6b99e43b93bf8e73fc210d2925322eacc;p=deliverable%2Flinux.git

drm/amdgpu: cleanup amdgpu_fence_activity

The comment about the loop counter was never valid, even when you have
multiple threads this loop only runs as long as the sequence increases.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
---

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
index 3db18f42c5c9..35fbc8874514 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
@@ -166,30 +166,8 @@ static void amdgpu_fence_schedule_fallback(struct amdgpu_ring *ring)
 static bool amdgpu_fence_activity(struct amdgpu_ring *ring)
 {
 	uint64_t seq, last_seq, last_emitted;
-	unsigned count_loop = 0;
 	bool wake = false;
 
-	/* Note there is a scenario here for an infinite loop but it's
-	 * very unlikely to happen. For it to happen, the current polling
-	 * process need to be interrupted by another process and another
-	 * process needs to update the last_seq btw the atomic read and
-	 * xchg of the current process.
-	 *
-	 * More over for this to go in infinite loop there need to be
-	 * continuously new fence signaled ie amdgpu_fence_read needs
-	 * to return a different value each time for both the currently
-	 * polling process and the other process that xchg the last_seq
-	 * btw atomic read and xchg of the current process. And the
-	 * value the other process set as last seq must be higher than
-	 * the seq value we just read. Which means that current process
-	 * need to be interrupted after amdgpu_fence_read and before
-	 * atomic xchg.
-	 *
-	 * To be even more safe we count the number of time we loop and
-	 * we bail after 10 loop just accepting the fact that we might
-	 * have temporarly set the last_seq not to the true real last
-	 * seq but to an older one.
-	 */
 	last_seq = atomic64_read(&ring->fence_drv.last_seq);
 	do {
 		last_emitted = ring->fence_drv.sync_seq;
@@ -200,23 +178,16 @@ static bool amdgpu_fence_activity(struct amdgpu_ring *ring)
 			seq |= last_emitted & 0xffffffff00000000LL;
 		}
 
-		if (seq <= last_seq || seq > last_emitted) {
+		if (seq <= last_seq || seq > last_emitted)
 			break;
-		}
+
 		/* If we loop over we don't want to return without
 		 * checking if a fence is signaled as it means that the
 		 * seq we just read is different from the previous on.
 		 */
 		wake = true;
 		last_seq = seq;
-		if ((count_loop++) > 10) {
-			/* We looped over too many time leave with the
-			 * fact that we might have set an older fence
-			 * seq then the current real last seq as signaled
-			 * by the hw.
-			 */
-			break;
-		}
+
 	} while (atomic64_xchg(&ring->fence_drv.last_seq, seq) > seq);
 
 	if (seq < last_emitted)