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From:   Rob Clark <robdclark@gmail.com>
To:     dri-devel@lists.freedesktop.org
Cc:     Rob Clark <robdclark@chromium.org>,
        Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        linux-arm-msm@vger.kernel.org (open list:DRM DRIVER FOR MSM ADRENO GPU),
        freedreno@lists.freedesktop.org (open list:DRM DRIVER FOR MSM ADRENO
        GPU), linux-kernel@vger.kernel.org (open list)
Subject: [PATCH 14/14] drm/msm: Don't implicit-sync if only a single ring
Date:   Sun,  4 Oct 2020 12:21:46 -0700
Message-Id: <20201004192152.3298573-15-robdclark@gmail.com>
In-Reply-To: <20201004192152.3298573-1-robdclark@gmail.com>
References: <20201004192152.3298573-1-robdclark@gmail.com>
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From: Rob Clark <robdclark@chromium.org>

Any cross-device sync use-cases *must* use explicit sync.  And if there
is only a single ring (no-preemption), everything is FIFO order and
there is no need to implicit-sync.

Mesa should probably just always use MSM_SUBMIT_NO_IMPLICIT, as behavior
is undefined when fences are not used to synchronize buffer usage across
contexts (which is the only case where multiple different priority rings
could come into play).

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/msm/msm_gem_submit.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index 7d653bdc92dc..b9b68153b7b2 100644
--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -219,7 +219,7 @@ static int submit_lock_objects(struct msm_gem_submit *submit)
 	return ret;
 }
 
-static int submit_fence_sync(struct msm_gem_submit *submit, bool no_implicit)
+static int submit_fence_sync(struct msm_gem_submit *submit, bool implicit_sync)
 {
 	int i, ret = 0;
 
@@ -239,7 +239,7 @@ static int submit_fence_sync(struct msm_gem_submit *submit, bool no_implicit)
 				return ret;
 		}
 
-		if (no_implicit)
+		if (!implicit_sync)
 			continue;
 
 		ret = msm_gem_sync_object(&msm_obj->base, submit->ring->fctx,
@@ -704,7 +704,8 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 	if (ret)
 		goto out;
 
-	ret = submit_fence_sync(submit, !!(args->flags & MSM_SUBMIT_NO_IMPLICIT));
+	ret = submit_fence_sync(submit, (gpu->nr_rings > 1) &&
+			!(args->flags & MSM_SUBMIT_NO_IMPLICIT));
 	if (ret)
 		goto out;
 
-- 
2.26.2