[PATCH 1/2] drm/syncobj: add sideband payload

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The Vulkan timeline semaphores allow signaling to happen on the point
of the timeline without all of the its dependencies to be created.

The current 2 implementations (AMD/Intel) of the Vulkan spec on top of
the Linux kernel are using a thread to wait on the dependencies of a
given point to materialize and delay actual submission to the kernel
driver until the wait completes.

If a binary semaphore is submitted for signaling along the side of a
timeline semaphore waiting for completion that means that the drm
syncobj associated with that binary semaphore will not have a DMA
fence associated with it by the time vkQueueSubmit() returns. This and
the fact that a binary semaphore can be signaled and unsignaled as
before its DMA fences materialize mean that we cannot just rely on the
fence within the syncobj but we also need a sideband payload verifying
that the fence in the syncobj matches the last submission from the
Vulkan API point of view.

This change adds a sideband payload that is incremented with signaled
syncobj when vkQueueSubmit() is called. The next vkQueueSubmit()
waiting on a the syncobj will read the sideband payload and wait for a
fence chain element with a seqno superior or equal to the sideband
payload value to be added into the fence chain and use that fence to
trigger the submission on the kernel driver.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
---
 drivers/gpu/drm/drm_syncobj.c | 119 +++++++++++++++++++++-------------
 include/drm/drm_syncobj.h     |   9 +++
 include/uapi/drm/drm.h        |   4 +-
 3 files changed, 86 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index b927e482e554..c437fb6aaf7c 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -1150,8 +1150,10 @@ drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,
 	if (ret < 0)
 		return ret;
 
-	for (i = 0; i < args->count_handles; i++)
+	for (i = 0; i < args->count_handles; i++) {
 		drm_syncobj_replace_fence(syncobjs[i], NULL);
+		syncobjs[i]->sideband_payload = 0;
+	}
 
 	drm_syncobj_array_free(syncobjs, args->count_handles);
 
@@ -1197,7 +1199,7 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
 {
 	struct drm_syncobj_timeline_array *args = data;
 	struct drm_syncobj **syncobjs;
-	struct dma_fence_chain **chains;
+	struct dma_fence_chain **chains = NULL;
 	uint64_t *points;
 	uint32_t i, j;
 	int ret;
@@ -1205,7 +1207,8 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
 	if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE))
 		return -EOPNOTSUPP;
 
-	if (args->pad != 0)
+	if (args->selector != DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIGNALED_POINT &&
+	    args->selector != DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIDEBAND_PAYLOAD)
 		return -EINVAL;
 
 	if (args->count_handles == 0)
@@ -1232,30 +1235,41 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
 		goto err_points;
 	}
 
-	chains = kmalloc_array(args->count_handles, sizeof(void *), GFP_KERNEL);
-	if (!chains) {
-		ret = -ENOMEM;
-		goto err_points;
-	}
-	for (i = 0; i < args->count_handles; i++) {
-		chains[i] = kzalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
-		if (!chains[i]) {
-			for (j = 0; j < i; j++)
-				kfree(chains[j]);
+	switch (args->selector) {
+	case DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIGNALED_POINT:
+		chains = kmalloc_array(args->count_handles, sizeof(void *), GFP_KERNEL);
+		if (!chains) {
 			ret = -ENOMEM;
-			goto err_chains;
+			goto err_points;
+		}
+		for (i = 0; i < args->count_handles; i++) {
+			chains[i] = kzalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
+			if (!chains[i]) {
+				for (j = 0; j < i; j++)
+					kfree(chains[j]);
+				ret = -ENOMEM;
+				goto err_chains;
+			}
 		}
-	}
 
-	for (i = 0; i < args->count_handles; i++) {
-		struct dma_fence *fence = dma_fence_get_stub();
+		for (i = 0; i < args->count_handles; i++) {
+			struct dma_fence *fence = dma_fence_get_stub();
 
-		drm_syncobj_add_point(syncobjs[i], chains[i],
-				      fence, points[i]);
-		dma_fence_put(fence);
+			drm_syncobj_add_point(syncobjs[i], chains[i],
+					      fence, points[i]);
+			dma_fence_put(fence);
+		}
+		break;
+
+	case DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIDEBAND_PAYLOAD:
+		for (i = 0; i < args->count_handles; i++)
+			syncobjs[i]->sideband_payload = points[i];
+		break;
 	}
+
 err_chains:
-	kfree(chains);
+	if (chains)
+		kfree(chains);
 err_points:
 	kfree(points);
 out:
@@ -1276,7 +1290,8 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
 	if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE))
 		return -EOPNOTSUPP;
 
-	if (args->pad != 0)
+	if (args->selector != DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIGNALED_POINT &&
+	    args->selector != DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIDEBAND_PAYLOAD)
 		return -EINVAL;
 
 	if (args->count_handles == 0)
@@ -1290,37 +1305,51 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
 		return ret;
 
 	for (i = 0; i < args->count_handles; i++) {
-		struct dma_fence_chain *chain;
 		struct dma_fence *fence;
+		struct dma_fence_chain *chain;
 		uint64_t point;
 
-		fence = drm_syncobj_fence_get(syncobjs[i]);
-		chain = to_dma_fence_chain(fence);
-		if (chain) {
-			struct dma_fence *iter, *last_signaled = NULL;
-
-			dma_fence_chain_for_each(iter, fence) {
-				if (iter->context != fence->context) {
-					dma_fence_put(iter);
-					/* It is most likely that timeline has
-					 * unorder points. */
-					break;
+		switch (args->selector) {
+		case DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIGNALED_POINT:
+			fence = drm_syncobj_fence_get(syncobjs[i]);
+			chain = to_dma_fence_chain(fence);
+			if (chain) {
+				struct dma_fence *iter, *last_signaled = NULL;
+
+				dma_fence_chain_for_each(iter, fence) {
+					if (iter->context != fence->context) {
+						dma_fence_put(iter);
+						/* It is most likely that
+						 * timeline has unorder
+						 * points. */
+						break;
+					}
+					dma_fence_put(last_signaled);
+					last_signaled = dma_fence_get(iter);
 				}
+				point = dma_fence_is_signaled(last_signaled) ?
+					last_signaled->seqno :
+					to_dma_fence_chain(last_signaled)->prev_seqno;
 				dma_fence_put(last_signaled);
-				last_signaled = dma_fence_get(iter);
+			} else {
+				point = 0;
 			}
-			point = dma_fence_is_signaled(last_signaled) ?
-				last_signaled->seqno :
-				to_dma_fence_chain(last_signaled)->prev_seqno;
-			dma_fence_put(last_signaled);
-		} else {
-			point = 0;
-		}
-		ret = copy_to_user(&points[i], &point, sizeof(uint64_t));
-		ret = ret ? -EFAULT : 0;
-		if (ret)
+			ret = copy_to_user(&points[i], &point, sizeof(uint64_t));
+			ret = ret ? -EFAULT : 0;
+			if (ret)
+				goto error;
+			break;
+
+		case DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIDEBAND_PAYLOAD:
+			copy_to_user(&points[i], &syncobjs[i]->sideband_payload, sizeof(uint64_t));
+			ret = ret ? -EFAULT : 0;
+			if (ret)
+				goto error;
 			break;
+		}
 	}
+
+error:
 	drm_syncobj_array_free(syncobjs, args->count_handles);
 
 	return ret;
diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
index 6cf7243a1dc5..b587b8e07547 100644
--- a/include/drm/drm_syncobj.h
+++ b/include/drm/drm_syncobj.h
@@ -61,6 +61,15 @@ struct drm_syncobj {
 	 * @file: A file backing for this syncobj.
 	 */
 	struct file *file;
+	/**
+	 * @sideband_payload: A 64bit side band payload.
+	 *
+	 * We use the sideband payload value to wait on binary syncobj fences
+	 * to materialize. It is a reservation mechanism for the signaler to
+	 * express that at some point in the future a dma fence with the same
+	 * seqno will be put into the syncobj.
+	 */
+	u64 sideband_payload;
 };
 
 void drm_syncobj_free(struct kref *kref);
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index 8a5b2f8f8eb9..dea759a36d37 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -782,7 +782,9 @@ struct drm_syncobj_timeline_array {
 	__u64 handles;
 	__u64 points;
 	__u32 count_handles;
-	__u32 pad;
+	__u32 selector;
+#define DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIGNALED_POINT   (0)
+#define DRM_SYNCOBJ_TIMELINE_ARRAY_SELECTOR_SIDEBAND_PAYLOAD (1)
 };
 
 
-- 
2.23.0.rc1

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