Revert "drm/virtio: drop prime import/export callbacks"

This patch does more harm than good, as it breaks both Xwayland and
gnome-shell with X11.

Xwayland requires DRI3 & DRI3 requires PRIME.

X11 crash for obscure double-free reason which are hard to debug
(starting X11 by hand doesn't trigger the crash).

I don't see an apparent problem implementing those stub prime
functions, they may return an error at run-time, and it seems to be
handled fine by GNOME at least.

This reverts commit b318e3f.
[airlied:
This broke userspace for virtio-gpus, and regressed things from DRI3 to DRI2.

This brings back the original problem, but it's better than regressions.]

Fixes: b318e3f ("drm/virtio: drop prime import/export callbacks")
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/virtio/virtgpu_drv.c

@@ -205,10 +205,14 @@ 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,
+	.prime_fd_to_handle = drm_gem_prime_fd_to_handle,
 	.gem_prime_export = drm_gem_prime_export,
 	.gem_prime_import = drm_gem_prime_import,
 	.gem_prime_pin = virtgpu_gem_prime_pin,
 	.gem_prime_unpin = virtgpu_gem_prime_unpin,
+	.gem_prime_get_sg_table = virtgpu_gem_prime_get_sg_table,
+	.gem_prime_import_sg_table = virtgpu_gem_prime_import_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

@@ -354,6 +354,10 @@ int virtio_gpu_object_wait(struct virtio_gpu_object *bo, bool no_wait);
 /* virtgpu_prime.c */
 int virtgpu_gem_prime_pin(struct drm_gem_object *obj);
 void virtgpu_gem_prime_unpin(struct drm_gem_object *obj);
+struct sg_table *virtgpu_gem_prime_get_sg_table(struct drm_gem_object *obj);
+struct drm_gem_object *virtgpu_gem_prime_import_sg_table(
+	struct drm_device *dev, struct dma_buf_attachment *attach,
+	struct sg_table *sgt);
 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

@@ -39,6 +39,18 @@ void virtgpu_gem_prime_unpin(struct drm_gem_object *obj)
 	WARN_ONCE(1, "not implemented");
 }
 
+struct sg_table *virtgpu_gem_prime_get_sg_table(struct drm_gem_object *obj)
+{
+	return ERR_PTR(-ENODEV);
+}
+
+struct drm_gem_object *virtgpu_gem_prime_import_sg_table(
+	struct drm_device *dev, struct dma_buf_attachment *attach,
+	struct sg_table *table)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 void *virtgpu_gem_prime_vmap(struct drm_gem_object *obj)
 {
 	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);