drm/virtio: add uapi for in and out explicit fences

Add a new field called fence_fd that will be used by userspace to send
in-fences to the kernel and receive out-fences created by the kernel.

This uapi enables virtio to take advantage of explicit synchronization of
dma-bufs.

There are two new flags:

* VIRTGPU_EXECBUF_FENCE_FD_IN to be used when passing an in-fence fd.
* VIRTGPU_EXECBUF_FENCE_FD_OUT to be used when requesting an out-fence fd

The execbuffer IOCTL is now read-write to allow the userspace to read the
out-fence.

On error -1 should be returned in the fence_fd field.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20181112165157.32765-3-robert.foss@collabora.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_ioctl.c

@@ -119,6 +119,11 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 	if (vgdev->has_virgl_3d == false)
 		return -ENOSYS;
 
+	if ((exbuf->flags & ~VIRTGPU_EXECBUF_FLAGS))
+		return -EINVAL;
+
+	exbuf->fence_fd = -1;
+
 	INIT_LIST_HEAD(&validate_list);
 	if (exbuf->num_bo_handles) {
 

include/uapi/drm/virtgpu_drm.h

@@ -47,6 +47,13 @@ extern "C" {
 #define DRM_VIRTGPU_WAIT     0x08
 #define DRM_VIRTGPU_GET_CAPS  0x09
 
+#define VIRTGPU_EXECBUF_FENCE_FD_IN	0x01
+#define VIRTGPU_EXECBUF_FENCE_FD_OUT	0x02
+#define VIRTGPU_EXECBUF_FLAGS  (\
+		VIRTGPU_EXECBUF_FENCE_FD_IN |\
+		VIRTGPU_EXECBUF_FENCE_FD_OUT |\
+		0)
+
 struct drm_virtgpu_map {
 	__u64 offset; /* use for mmap system call */
 	__u32 handle;
@@ -54,12 +61,12 @@ struct drm_virtgpu_map {
 };
 
 struct drm_virtgpu_execbuffer {
-	__u32		flags;		/* for future use */
+	__u32 flags;
 	__u32 size;
 	__u64 command; /* void* */
 	__u64 bo_handles;
 	__u32 num_bo_handles;
-	__u32 pad;
+	__s32 fence_fd;
 };
 
 #define VIRTGPU_PARAM_3D_FEATURES 1 /* do we have 3D features in the hw */
@@ -137,7 +144,7 @@ struct drm_virtgpu_get_caps {
 	DRM_IOWR(DRM_COMMAND_BASE + DRM_VIRTGPU_MAP, struct drm_virtgpu_map)
 
 #define DRM_IOCTL_VIRTGPU_EXECBUFFER \
-	DRM_IOW(DRM_COMMAND_BASE + DRM_VIRTGPU_EXECBUFFER,\
+	DRM_IOWR(DRM_COMMAND_BASE + DRM_VIRTGPU_EXECBUFFER,\
 		struct drm_virtgpu_execbuffer)
 
 #define DRM_IOCTL_VIRTGPU_GETPARAM \