dma-buf: keep the signaling time of merged fences v3

Some Android CTS is testing if the signaling time keeps consistent
during merges.

v2: use the current time if the fence is still in the signaling path and
the timestamp not yet available.
v3: improve comment, fix one more case to use the correct timestamp

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230630120041.109216-1-christian.koenig@amd.com

Author: ChristianKoenigAMD

drivers/dma-buf/dma-fence-unwrap.c

@@ -66,18 +66,36 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
 {
 	struct dma_fence_array *result;
 	struct dma_fence *tmp, **array;
+	ktime_t timestamp;
 	unsigned int i;
 	size_t count;
 
 	count = 0;
+	timestamp = ns_to_ktime(0);
 	for (i = 0; i < num_fences; ++i) {
-		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
-			if (!dma_fence_is_signaled(tmp))
+		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
+			if (!dma_fence_is_signaled(tmp)) {
 				++count;
+			} else if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT,
+					    &tmp->flags)) {
+				if (ktime_after(tmp->timestamp, timestamp))
+					timestamp = tmp->timestamp;
+			} else {
+				/*
+				 * Use the current time if the fence is
+				 * currently signaling.
+				 */
+				timestamp = ktime_get();
+			}
+		}
 	}
 
+	/*
+	 * If we couldn't find a pending fence just return a private signaled
+	 * fence with the timestamp of the last signaled one.
+	 */
 	if (count == 0)
-		return dma_fence_get_stub();
+		return dma_fence_allocate_private_stub(timestamp);
 
 	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
 	if (!array)
@@ -138,7 +156,7 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
 	} while (tmp);
 
 	if (count == 0) {
-		tmp = dma_fence_get_stub();
+		tmp = dma_fence_allocate_private_stub(ktime_get());
 		goto return_tmp;
 	}
 

drivers/dma-buf/dma-fence.c

@@ -150,10 +150,11 @@ EXPORT_SYMBOL(dma_fence_get_stub);
 
 /**
  * dma_fence_allocate_private_stub - return a private, signaled fence
+ * @timestamp: timestamp when the fence was signaled
  *
  * Return a newly allocated and signaled stub fence.
  */
-struct dma_fence *dma_fence_allocate_private_stub(void)
+struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp)
 {
 	struct dma_fence *fence;
 
@@ -169,7 +170,7 @@ struct dma_fence *dma_fence_allocate_private_stub(void)
 	set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
 		&fence->flags);
 
-	dma_fence_signal(fence);
+	dma_fence_signal_timestamp(fence, timestamp);
 
 	return fence;
 }

drivers/gpu/drm/drm_syncobj.c

@@ -353,7 +353,7 @@ EXPORT_SYMBOL(drm_syncobj_replace_fence);
  */
 static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
 {
-	struct dma_fence *fence = dma_fence_allocate_private_stub();
+	struct dma_fence *fence = dma_fence_allocate_private_stub(ktime_get());
 
 	if (IS_ERR(fence))
 		return PTR_ERR(fence);

include/linux/dma-fence.h

@@ -606,7 +606,7 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
 void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
 
 struct dma_fence *dma_fence_get_stub(void);
-struct dma_fence *dma_fence_allocate_private_stub(void);
+struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp);
 u64 dma_fence_context_alloc(unsigned num);
 
 extern const struct dma_fence_ops dma_fence_array_ops;