drm: Create a driver hook for allocating GEM object structs.

The CMA helpers had no way for a driver to extend the struct with its
own fields.  Since the CMA helpers are mostly "Allocate a
drm_gem_cma_object, then fill in a few fields", it's hard to write as
pure helpers without passing in a driver callback for the allocate
step.
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_gem_cma_helper.c

@@ -59,11 +59,13 @@ __drm_gem_cma_create(struct drm_device *drm, size_t size)
 	struct drm_gem_object *gem_obj;
 	int ret;
 
-	cma_obj = kzalloc(sizeof(*cma_obj), GFP_KERNEL);
-	if (!cma_obj)
+	if (drm->driver->gem_create_object)
+		gem_obj = drm->driver->gem_create_object(drm, size);
+	else
+		gem_obj = kzalloc(sizeof(*cma_obj), GFP_KERNEL);
+	if (!gem_obj)
 		return ERR_PTR(-ENOMEM);
-
-	gem_obj = &cma_obj->base;
+	cma_obj = container_of(gem_obj, struct drm_gem_cma_object, base);
 
 	ret = drm_gem_object_init(drm, gem_obj, size);
 	if (ret)

include/drm/drmP.h

@@ -580,6 +580,13 @@ struct drm_driver {
 	int (*gem_open_object) (struct drm_gem_object *, struct drm_file *);
 	void (*gem_close_object) (struct drm_gem_object *, struct drm_file *);
 
+	/**
+	 * Hook for allocating the GEM object struct, for use by core
+	 * helpers.
+	 */
+	struct drm_gem_object *(*gem_create_object)(struct drm_device *dev,
+						    size_t size);
+
 	/* prime: */
 	/* export handle -> fd (see drm_gem_prime_handle_to_fd() helper) */
 	int (*prime_handle_to_fd)(struct drm_device *dev, struct drm_file *file_priv,