drm/atomic-helper: make drm_gem_plane_helper_prepare_fb the default

There's a bunch of atomic drivers who don't do this quite correctly,
luckily most of them aren't in wide use or people would have noticed
the tearing.

By making this the default we avoid the constant audit pain and can
additionally remove a ton of lines from vfuncs for a bit more clarity
in smaller drivers.

While at it complain if there's a cleanup_fb hook but no prepare_fb
hook, because that makes no sense. I haven't found any driver which
violates this, but better safe than sorry.

Subsequent patches will reap the benefits.

v2: It's neither ... nor, not not (Sam)

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210623162200.3372056-1-daniel.vetter@ffwll.ch

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_gem_atomic_helper.c b/drivers/gpu/drm/drm_gem_atomic_helper.c
index a27135084ae5..bc9396f2a0ed 100644
--- a/drivers/gpu/drm/drm_gem_atomic_helper.c
+++ b/drivers/gpu/drm/drm_gem_atomic_helper.c
@@ -135,6 +135,9 @@
  * GEM based framebuffer drivers which have their buffers always pinned in
  * memory.
  *
+ * This function is the default implementation for GEM drivers of
+ * &drm_plane_helper_funcs.prepare_fb if no callback is provided.
+ *
  * See drm_atomic_set_fence_for_plane() for a discussion of implicit and
  * explicit fencing in atomic modeset updates.
  */