drm/v3d: Explicitly get and put drm-shmem pages

To simplify the drm-shmem refcnt handling, we're moving away from
the implicit get_pages() that is used by get_pages_sgt(). From now on
drivers will have to pin pages while they use sgt. V3D driver doesn't
support shrinker, hence pages are pinned and sgt is valid as long as
pages' use-count > 0.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

drivers/gpu/drm/v3d/v3d_bo.c

@@ -58,6 +58,9 @@ void v3d_free_object(struct drm_gem_object *obj)
 	/* GPU execution may have dirtied any pages in the BO. */
 	bo->base.pages_mark_dirty_on_put = true;
 
+	if (!drm_gem_is_imported(obj))
+		drm_gem_shmem_put_pages(&bo->base);
+
 	drm_gem_shmem_free(&bo->base);
 }
 
@@ -160,12 +163,18 @@ struct v3d_bo *v3d_bo_create(struct drm_device *dev, struct drm_file *file_priv,
 	bo = to_v3d_bo(&shmem_obj->base);
 	bo->vaddr = NULL;
 
-	ret = v3d_bo_create_finish(&shmem_obj->base);
+	ret = drm_gem_shmem_get_pages(shmem_obj);
 	if (ret)
 		goto free_obj;
 
+	ret = v3d_bo_create_finish(&shmem_obj->base);
+	if (ret)
+		goto put_pages;
+
 	return bo;
 
+put_pages:
+	drm_gem_shmem_put_pages(shmem_obj);
 free_obj:
 	drm_gem_shmem_free(shmem_obj);
 	return ERR_PTR(ret);