[PATCH v2 1/1] 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.

v2: Use a separate ioctl to get/set the sideband value (Christian)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
Cc: Christian Koenig <Christian.Koenig@xxxxxxx>
Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Cc: David(ChunMing) Zhou <David1.Zhou@xxxxxxx>
---
 drivers/gpu/drm/drm_internal.h |  2 ++
 drivers/gpu/drm/drm_ioctl.c    |  3 ++
 drivers/gpu/drm/drm_syncobj.c  | 63 +++++++++++++++++++++++++++++++---
 include/drm/drm_syncobj.h      |  9 +++++
 include/uapi/drm/drm.h         |  5 ++-
 5 files changed, 77 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
index 51a2055c8f18..de5267711a7c 100644
--- a/drivers/gpu/drm/drm_internal.h
+++ b/drivers/gpu/drm/drm_internal.h
@@ -208,6 +208,8 @@ int drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
 				      struct drm_file *file_private);
 int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
 			    struct drm_file *file_private);
+int drm_syncobj_sideband_ioctl(struct drm_device *dev, void *data,
+			       struct drm_file *file_private);
 
 /* drm_framebuffer.c */
 void drm_framebuffer_print_info(struct drm_printer *p, unsigned int indent,
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index f675a3bb2c88..7fd99533f78f 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -703,6 +703,9 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
 		      DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_QUERY, drm_syncobj_query_ioctl,
 		      DRM_RENDER_ALLOW),
+	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_SIDEBAND, drm_syncobj_sideband_ioctl,
+		      DRM_RENDER_ALLOW),
+
 	DRM_IOCTL_DEF(DRM_IOCTL_CRTC_GET_SEQUENCE, drm_crtc_get_sequence_ioctl, 0),
 	DRM_IOCTL_DEF(DRM_IOCTL_CRTC_QUEUE_SEQUENCE, drm_crtc_queue_sequence_ioctl, 0),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_CREATE_LEASE, drm_mode_create_lease_ioctl, DRM_MASTER),
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index b927e482e554..66f4f91baa6d 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);
 
@@ -1205,7 +1207,7 @@ 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->flags != 0)
 		return -EINVAL;
 
 	if (args->count_handles == 0)
@@ -1276,7 +1278,7 @@ 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->flags != 0)
 		return -EINVAL;
 
 	if (args->count_handles == 0)
@@ -1312,15 +1314,68 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
 			point = dma_fence_is_signaled(last_signaled) ?
 				last_signaled->seqno :
 				to_dma_fence_chain(last_signaled)->prev_seqno;
-			dma_fence_put(last_signaled);
+				dma_fence_put(last_signaled);
 		} else {
 			point = 0;
 		}
 		ret = copy_to_user(&points[i], &point, sizeof(uint64_t));
 		ret = ret ? -EFAULT : 0;
 		if (ret)
+			goto error;
+		break;
+	}
+
+error:
+	drm_syncobj_array_free(syncobjs, args->count_handles);
+
+	return ret;
+}
+
+int drm_syncobj_sideband_ioctl(struct drm_device *dev, void *data,
+			       struct drm_file *file_private)
+{
+	struct drm_syncobj_timeline_array *args = data;
+	struct drm_syncobj **syncobjs;
+	uint64_t __user *points = u64_to_user_ptr(args->points);
+	uint32_t i;
+	int ret;
+
+	if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE))
+		return -EOPNOTSUPP;
+
+	if (args->flags != DRM_SYNCOBJ_TIMELINE_ARRAY_GET_SIDEBAND_PAYLOAD &&
+	    args->flags != DRM_SYNCOBJ_TIMELINE_ARRAY_SET_SIDEBAND_PAYLOAD)
+		return -EINVAL;
+
+	if (args->count_handles == 0)
+		return -EINVAL;
+
+	ret = drm_syncobj_array_find(file_private,
+				     u64_to_user_ptr(args->handles),
+				     args->count_handles,
+				     &syncobjs);
+	if (ret < 0)
+		return ret;
+
+	for (i = 0; i < args->count_handles; i++) {
+		switch (args->flags) {
+		case DRM_SYNCOBJ_TIMELINE_ARRAY_GET_SIDEBAND_PAYLOAD:
+			copy_to_user(&points[i], &syncobjs[i]->sideband_payload, sizeof(uint64_t));
+			ret = ret ? -EFAULT : 0;
+			if (ret)
+				goto error;
+			break;
+
+		case DRM_SYNCOBJ_TIMELINE_ARRAY_SET_SIDEBAND_PAYLOAD:
+			copy_from_user(&syncobjs[i]->sideband_payload, &points[i], 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..dfcbaf603aff 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 flags;
+#define DRM_SYNCOBJ_TIMELINE_ARRAY_GET_SIDEBAND_PAYLOAD (0)
+#define DRM_SYNCOBJ_TIMELINE_ARRAY_SET_SIDEBAND_PAYLOAD (1)
 };
 
 
@@ -946,6 +948,7 @@ extern "C" {
 #define DRM_IOCTL_SYNCOBJ_QUERY		DRM_IOWR(0xCB, struct drm_syncobj_timeline_array)
 #define DRM_IOCTL_SYNCOBJ_TRANSFER	DRM_IOWR(0xCC, struct drm_syncobj_transfer)
 #define DRM_IOCTL_SYNCOBJ_TIMELINE_SIGNAL	DRM_IOWR(0xCD, struct drm_syncobj_timeline_array)
+#define DRM_IOCTL_SYNCOBJ_SIDEBAND	DRM_IOWR(0xCE, struct drm_syncobj_timeline_array)
 
 /**
  * Device specific ioctls should only be in their respective headers
-- 
2.23.0.rc1

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