linux-kernel - [PATCH] drm/msm: Fix fence rollover issue

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Date:   Wed, 15 Jun 2022 09:24:35 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/msm: Fix fence rollover issue

From: Rob Clark <robdclark@...omium.org>

And while we are at it, let's start the fence counter close to the
rollover point so that if issues slip in, they are more obvious.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/msm/msm_fence.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_fence.c b/drivers/gpu/drm/msm/msm_fence.c
index 3df255402a33..a35a6746c7cd 100644
--- a/drivers/gpu/drm/msm/msm_fence.c
+++ b/drivers/gpu/drm/msm/msm_fence.c
@@ -28,6 +28,14 @@ msm_fence_context_alloc(struct drm_device *dev, volatile uint32_t *fenceptr,
 	fctx->fenceptr = fenceptr;
 	spin_lock_init(&fctx->spinlock);
 
+	/*
+	 * Start out close to the 32b fence rollover point, so we can
+	 * catch bugs with fence comparisons.
+	 */
+	fctx->last_fence = 0xffffff00;
+	fctx->completed_fence = fctx->last_fence;
+	*fctx->fenceptr = fctx->last_fence;
+
 	return fctx;
 }
 
@@ -46,11 +54,12 @@ bool msm_fence_completed(struct msm_fence_context *fctx, uint32_t fence)
 		(int32_t)(*fctx->fenceptr - fence) >= 0;
 }
 
-/* called from workqueue */
+/* called from irq handler */
 void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence)
 {
 	spin_lock(&fctx->spinlock);
-	fctx->completed_fence = max(fence, fctx->completed_fence);
+	if (fence_after(fence, fctx->completed_fence))
+		fctx->completed_fence = fence;
 	spin_unlock(&fctx->spinlock);
 }
 
-- 
2.36.1