Adding format modifiers without implementing the function "drm_plane_funcs.format_mod_supported" exposes an invalid IN_FORMATS blob with modifiers but no formats to user-space. This breaks the latest Weston [1]. For testing purposes, I extracted the affected code to a standalone program [2]. Make clear in the IN_FORMATS documentation that implementing "format_mod_supported" is mandatory. [1] https://gitlab.freedesktop.org/wayland/weston/-/blob/9.0/libweston/backend-drm/kms.c#L431 [2] https://github.com/JoseExposito/drm-sandbox/blob/main/in_formats.c Signed-off-by: José Expósito <jose.exposito89@xxxxxxxxx> --- drivers/gpu/drm/drm_plane.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c index 82afb854141b..347571f8909a 100644 --- a/drivers/gpu/drm/drm_plane.c +++ b/drivers/gpu/drm/drm_plane.c @@ -126,8 +126,11 @@ * IN_FORMATS: * Blob property which contains the set of buffer format and modifier * pairs supported by this plane. The blob is a struct - * drm_format_modifier_blob. Without this property the plane doesn't - * support buffers with modifiers. Userspace cannot change this property. + * drm_format_modifier_blob and the drm_plane_funcs.format_mod_supported + * function must be implemented by the driver to determine if the given + * format/modifier combination is valid for the plane. Without this property + * the plane doesn't support buffers with modifiers. Userspace cannot change + * this property. * * Note that userspace can check the &DRM_CAP_ADDFB2_MODIFIERS driver * capability for general modifier support. If this flag is set then every -- 2.25.1
