drm: add support modifiers for drivers whose planes only support linear layout

The LINEAR modifier is advertised as default if a driver doesn't specify
modifiers.

v2:
 - rebase to the latest master branch (5.16.0+)
    + "drm/plane: Make format_mod_supported truly optional" patch [1]
   [1] https://patchwork.freedesktop.org/patch/467940/?series=98255&rev=3

v3:
 - change the order as follows:
   1. add fb_modifiers_not_supported flag
   2. add default modifiers
   3. remove allow_fb_modifiers flag

v5:
 - change default_modifiers array from non-static to static
 - remove terminator in default_modifiers array
 - use ARRAY_SIZE to get the format_modifier_count
 - update sanity check in plane init func to use the
   fb_modifiers_not_supported
 - modify kernel docs

Signed-off-by: Tomohito Esaki <etom@igel.co.jp>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128060836.11216-3-etom@igel.co.jp

1 files changed, 3 insertions, 0 deletions

diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 06759badf99f..2628c7cde2da 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -803,6 +803,9 @@ void *__drmm_universal_plane_alloc(struct drm_device *dev,
  *
  * The @drm_plane_funcs.destroy hook must be NULL.
  *
+ * Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set
+ * @format_modifiers to NULL. The plane will advertise the linear modifier.
+ *
  * Returns:
  * Pointer to new plane, or ERR_PTR on failure.
  */