[PATCH v3 1/6] drm/plane: Make format_mod_supported truly optional

[José Expósito]

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 at gmail.com>
Reviewed-by: Simon Ser <contact at emersion.fr>

---

v2:

 - Remove unused "done:" label to fix compile warning
   Reported-by: kernel test robot <lkp at intel.com>

 - Add Reviewed-by (thanks to Simon Ser)
---
 drivers/gpu/drm/drm_plane.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 82afb854141b..deeec60a3315 100644
--- 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);
 
-- 
2.25.1