[PATCH] drm/msm: Fix fence rollover issue

Rob Clark
2022-06-15T16:24:27Z

From: Rob Clark <robdclark@chromium.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@chromium.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