drm/plane: Make format_mod_supported truly optional

The documentation for "drm_plane_funcs.format_mod_supported" reads:

  This *optional* hook is used for the DRM to determine if the given
  format/modifier combination is valid for the plane. This allows the
  DRM to generate the correct format bitmask (which formats apply to
  which modifier), and to validate modifiers at atomic_check time.

  *If not present*, then any modifier in the plane's modifier
  list is allowed with any of the plane's formats.

However, where the function is not present, an invalid IN_FORMATS blob
property with modifiers but no formats is exposed to user-space.

This breaks the latest Weston [1]. For testing purposes, I extracted the
affected code to a standalone program [2].

Make "create_in_format_blob" behave as documented.

[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@gmail.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20211226112503.31771-2-jose.exposito89@gmail.com

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 82afb854141b25c8711877950acc50adc7ce6f68..deeec60a3315a409991698287db9f847ccc842ab 100644 (file)
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -202,17 +202,13 @@ static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane
 
        memcpy(formats_ptr(blob_data), plane->format_types, formats_size);
 
-       /* If we can't determine support, just bail */
-       if (!plane->funcs->format_mod_supported)
-               goto done;
-
        mod = modifiers_ptr(blob_data);
        for (i = 0; i < plane->modifier_count; i++) {
                for (j = 0; j < plane->format_count; j++) {
-                       if (plane->funcs->format_mod_supported(plane,
+                       if (!plane->funcs->format_mod_supported ||
+                           plane->funcs->format_mod_supported(plane,
                                                               plane->format_types[j],
                                                               plane->modifiers[i])) {
-
                                mod->formats |= 1ULL << j;
                        }
                }
@@ -223,7 +219,6 @@ static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane
                mod++;
        }
 
-done:
        drm_object_attach_property(&plane->base, config->modifiers_property,
                                   blob->base.id);