drm/gem: Add a flag to control whether objects can be exported

Drivers may want to support driver-private objects, which cannot be
shared. This allows them to share a single lock and enables other
optimizations.

Add an `exportable` field to drm_gem_object, which blocks PRIME export
if set to false. It is initialized to true in
drm_gem_private_object_init.

Signed-off-by: Asahi Lina <lina@asahilina.net>

drivers/gpu/drm/drm_gem.c

@@ -169,6 +169,7 @@ void drm_gem_private_object_init(struct drm_device *dev,
 
 	drm_vma_node_reset(&obj->vma_node);
 	INIT_LIST_HEAD(&obj->lru_node);
+	obj->exportable = true;
 }
 EXPORT_SYMBOL(drm_gem_private_object_init);
 

drivers/gpu/drm/drm_prime.c

@@ -387,6 +387,11 @@ static struct dma_buf *export_and_register_object(struct drm_device *dev,
 		return dmabuf;
 	}
 
+	if (!obj->exportable) {
+		dmabuf = ERR_PTR(-EINVAL);
+		return dmabuf;
+	}
+
 	if (obj->funcs && obj->funcs->export)
 		dmabuf = obj->funcs->export(obj, flags);
 	else

include/drm/drm_gem.h

@@ -430,6 +430,14 @@ struct drm_gem_object {
 	 * The current LRU list that the GEM object is on.
 	 */
 	struct drm_gem_lru *lru;
+
+	/**
+	 * @exportable:
+	 *
+	 * Whether this GEM object can be exported via the drm_gem_object_funcs->export
+	 * callback. Defaults to true.
+	 */
+	bool exportable;
 };
 
 /**