drm/virtio: implement prime export

Just run drm_prime_pages_to_sg() on the ttm pages list to get an
sg_table for export.  The pages list is created at object initialization
time, so there should be no need to handle an unpopulated page list.
Add a sanity check nevertheless.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190227144441.6755-4-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_drv.c

@@ -205,8 +205,10 @@ static struct drm_driver driver = {
 #if defined(CONFIG_DEBUG_FS)
 	.debugfs_init = virtio_gpu_debugfs_init,
 #endif
+	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
 	.gem_prime_export = drm_gem_prime_export,
 	.gem_prime_import = drm_gem_prime_import,
+	.gem_prime_get_sg_table = virtgpu_gem_prime_get_sg_table,
 	.gem_prime_vmap = virtgpu_gem_prime_vmap,
 	.gem_prime_vunmap = virtgpu_gem_prime_vunmap,
 	.gem_prime_mmap = virtgpu_gem_prime_mmap,

drivers/gpu/drm/virtio/virtgpu_drv.h

@@ -352,6 +352,7 @@ void virtio_gpu_object_free_sg_table(struct virtio_gpu_object *bo);
 int virtio_gpu_object_wait(struct virtio_gpu_object *bo, bool no_wait);
 
 /* virtgpu_prime.c */
+struct sg_table *virtgpu_gem_prime_get_sg_table(struct drm_gem_object *obj);
 void *virtgpu_gem_prime_vmap(struct drm_gem_object *obj);
 void virtgpu_gem_prime_vunmap(struct drm_gem_object *obj, void *vaddr);
 int virtgpu_gem_prime_mmap(struct drm_gem_object *obj,

drivers/gpu/drm/virtio/virtgpu_prime.c

@@ -28,6 +28,18 @@
  * device that might share buffers with virtgpu
  */
 
+struct sg_table *virtgpu_gem_prime_get_sg_table(struct drm_gem_object *obj)
+{
+	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
+
+	if (!bo->tbo.ttm->pages || !bo->tbo.ttm->num_pages)
+		/* should not happen */
+		return ERR_PTR(-EINVAL);
+
+	return drm_prime_pages_to_sg(bo->tbo.ttm->pages,
+				     bo->tbo.ttm->num_pages);
+}
+
 void *virtgpu_gem_prime_vmap(struct drm_gem_object *obj)
 {
 	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);