drm: Update documentation and TODO of gem_prime_mmap hook

The hook gem_prime_mmap in struct drm_driver is deprecated. Document
the new requirements.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211108102846.309-4-tzimmermann@suse.de

Documentation/gpu/todo.rst

@@ -268,17 +268,6 @@ Contact: Daniel Vetter
 
 Level: Intermediate
 
-Clean up mmap forwarding
-------------------------
-
-A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
-And also a lot of them forward dma-buf mmap to the gem mmap implementations.
-There's drm_gem_prime_mmap() for this now, but still needs to be rolled out.
-
-Contact: Daniel Vetter
-
-Level: Intermediate
-
 Generic fbdev defio support
 ---------------------------
 

include/drm/drm_drv.h

@@ -345,11 +345,14 @@ struct drm_driver {
 	 * mmap hook for GEM drivers, used to implement dma-buf mmap in the
 	 * PRIME helpers.
 	 *
-	 * FIXME: There's way too much duplication going on here, and also moved
-	 * to &drm_gem_object_funcs.
+	 * This hook only exists for historical reasons. Drivers must use
+	 * drm_gem_prime_mmap() to implement it.
+	 *
+	 * FIXME: Convert all drivers to implement mmap in struct
+	 * &drm_gem_object_funcs and inline drm_gem_prime_mmap() into
+	 * its callers. This hook should be removed afterwards.
 	 */
-	int (*gem_prime_mmap)(struct drm_gem_object *obj,
-				struct vm_area_struct *vma);
+	int (*gem_prime_mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);
 
 	/**
 	 * @dumb_create: