drm/msm: Handle fence rollover

Add some helpers for fence comparision, which handle rollover properly,
and stop open coding fence seqno comparisions.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Akhil P Oommen <akhilpo@codeaurora.org>
Link: https://lore.kernel.org/r/20211109181117.591148-5-robdclark@gmail.com
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_drv.c

@@ -967,7 +967,7 @@ static int wait_fence(struct msm_gpu_submitqueue *queue, uint32_t fence_id,
 	struct dma_fence *fence;
 	int ret;
 
-	if (fence_id > queue->last_fence) {
+	if (fence_after(fence_id, queue->last_fence)) {
 		DRM_ERROR_RATELIMITED("waiting on invalid fence: %u (of %u)\n",
 				      fence_id, queue->last_fence);
 		return -EINVAL;

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;
+}
+
+static inline bool
+fence_after(uint32_t a, uint32_t b)
+{
+   return (int32_t)(a - b) > 0;
+}
+
 #endif

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: */

drivers/gpu/drm/msm/msm_gpu.h

@@ -262,7 +262,7 @@ 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;
 	}