From 4c2488cfaa997e396aeb9d6496db94c25b97c671 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>
Date: Mon, 5 Aug 2019 13:18:43 +0200
Subject: drm/i915: stop using seqcount for fence pruning
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Git-commit: 4c2488cfaa997e396aeb9d6496db94c25b97c671
Patch-mainline: v5.4-rc1
References: bsc#1152472

After waiting for a reservation object use reservation_object_test_signaled_rcu
to opportunistically prune the fences on the object.

This allows removal of the seqcount handling in the reservation object.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/322032/?series=64786&rev=1
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/i915/gem/i915_gem_wait.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
index 26ec6579b7cd..fa46a54bcbe7 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
@@ -35,7 +35,6 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 				 unsigned int flags,
 				 long timeout)
 {
-	unsigned int seq = __read_seqcount_begin(&resv->seq);
 	struct dma_fence *excl;
 	bool prune_fences = false;
 
@@ -83,15 +82,12 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 
 	/*
 	 * Opportunistically prune the fences iff we know they have *all* been
-	 * signaled and that the reservation object has not been changed (i.e.
-	 * no new fences have been added).
+	 * signaled.
 	 */
-	if (prune_fences && !__read_seqcount_retry(&resv->seq, seq)) {
-		if (reservation_object_trylock(resv)) {
-			if (!__read_seqcount_retry(&resv->seq, seq))
-				reservation_object_add_excl_fence(resv, NULL);
-			reservation_object_unlock(resv);
-		}
+	if (prune_fences && reservation_object_trylock(resv)) {
+		if (reservation_object_test_signaled_rcu(resv, true))
+			reservation_object_add_excl_fence(resv, NULL);
+		reservation_object_unlock(resv);
 	}
 
 	return timeout;
-- 
2.28.0