drm/virtio: add virtio_gpu_is_shmem helper

The plan is use have both shmem and virtual "vram" running
side-by-side in virtio-gpu. It looks like we'll eventually use
struct drm_gem_object as a base class, and we'll need to convert
to shmem and vram objects on the fly. As a first step, add a
virtio_gpu_is_shmem helper. Thanks to kraxel for suggesting this
approach on Gitlab.
Suggested-by: Gerd Hoffman <kraxel@redhat.com>
Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20200227002601.745-3-gurchetansingh@chromium.orgSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_drv.h

@@ -365,6 +365,9 @@ int virtio_gpu_object_create(struct virtio_gpu_device *vgdev,
 			     struct virtio_gpu_object_params *params,
 			     struct virtio_gpu_object **bo_ptr,
 			     struct virtio_gpu_fence *fence);
+
+bool virtio_gpu_is_shmem(struct drm_gem_object *obj);
+
 /* virtgpu_prime.c */
 struct drm_gem_object *virtgpu_gem_prime_import_sg_table(
 	struct drm_device *dev, struct dma_buf_attachment *attach,

drivers/gpu/drm/virtio/virtgpu_object.c

@@ -95,7 +95,7 @@ static void virtio_gpu_free_object(struct drm_gem_object *obj)
 	virtio_gpu_cleanup_object(bo);
 }
 
-static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
+static const struct drm_gem_object_funcs virtio_gpu_shmem_funcs = {
 	.free = virtio_gpu_free_object,
 	.open = virtio_gpu_gem_object_open,
 	.close = virtio_gpu_gem_object_close,
@@ -109,6 +109,11 @@ static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
 	.mmap = drm_gem_shmem_mmap,
 };
 
+bool virtio_gpu_is_shmem(struct drm_gem_object *obj)
+{
+	return obj->funcs == &virtio_gpu_shmem_funcs;
+}
+
 struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
 						size_t size)
 {
@@ -118,7 +123,7 @@ struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
 	if (!bo)
 		return NULL;
 
-	bo->base.base.funcs = &virtio_gpu_gem_funcs;
+	bo->base.base.funcs = &virtio_gpu_shmem_funcs;
 	return &bo->base.base;
 }