Re: [Freedreno] [PATCH 4/5] drm/msm: Handle fence rollover

[Akhil P Oommen]

On 11/9/2021 11:41 PM, Rob Clark wrote:
From: Rob Clark <robdcl...@chromium.org>
Add some helpers for fence comparision, which handle rollover properly,
and stop open coding fence seqno comparisions.

Signed-off-by: Rob Clark <robdcl...@chromium.org>
---
  drivers/gpu/drm/msm/msm_fence.h | 12 ++++++++++++
  drivers/gpu/drm/msm/msm_gpu.c   |  6 +++---
  drivers/gpu/drm/msm/msm_gpu.h   |  2 +-
  3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_fence.h b/drivers/gpu/drm/msm/msm_fence.h
index 4783db528bcc..17ee3822b423 100644
--- a/drivers/gpu/drm/msm/msm_fence.h
+++ b/drivers/gpu/drm/msm/msm_fence.h
@@ -60,4 +60,16 @@ void msm_update_fence(struct msm_fence_context *fctx, 
uint32_t fence);
  
  struct dma_fence * msm_fence_alloc(struct msm_fence_context *fctx);
  
+static inline bool
+fence_before(uint32_t a, uint32_t b)
+{
+   return (int32_t)(a - b) < 0;

This is good enough when a and b have close values. And that is a good 
assumption for KMD generated seqno.

Reviewed-by: Akhil P Oommen <akhi...@codeaurora.org>

-Akhil.

+}
+
+static inline bool
+fence_after(uint32_t a, uint32_t b)
+{
+   return (int32_t)(a - b) > 0;
+}
+
  #endif
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index 13de1241d595..0f78c2615272 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -172,7 +172,7 @@ static void update_fences(struct msm_gpu *gpu, struct 
msm_ringbuffer *ring,
  
  	spin_lock_irqsave(&ring->submit_lock, flags);
        list_for_each_entry(submit, &ring->submits, node) {
-               if (submit->seqno > fence)
+               if (fence_after(submit->seqno, fence))
                        break;
  
  		msm_update_fence(submit->ring->fctx,
@@ -509,7 +509,7 @@ static void hangcheck_handler(struct timer_list *t)
        if (fence != ring->hangcheck_fence) {
                /* some progress has been made.. ya! */
                ring->hangcheck_fence = fence;
-       } else if (fence < ring->seqno) {
+       } else if (fence_before(fence, ring->seqno)) {
                /* no progress and not done.. hung! */
                ring->hangcheck_fence = fence;
                DRM_DEV_ERROR(dev->dev, "%s: hangcheck detected gpu lockup rb 
%d!\n",
@@ -523,7 +523,7 @@ static void hangcheck_handler(struct timer_list *t)
        }
  
  	/* if still more pending work, reset the hangcheck timer: */
-       if (ring->seqno > ring->hangcheck_fence)
+       if (fence_after(ring->seqno, ring->hangcheck_fence))
                hangcheck_timer_reset(gpu);
  
  	/* workaround for missing irq: */
diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
index 0dcc31c27ac3..bd4e0024033e 100644
--- a/drivers/gpu/drm/msm/msm_gpu.h
+++ b/drivers/gpu/drm/msm/msm_gpu.h
@@ -258,7 +258,7 @@ static inline bool msm_gpu_active(struct msm_gpu *gpu)
        for (i = 0; i < gpu->nr_rings; i++) {
                struct msm_ringbuffer *ring = gpu->rb[i];
  
-		if (ring->seqno > ring->memptrs->fence)
+               if (fence_after(ring->seqno, ring->memptrs->fence))
                        return true;
        }