On Mon, May 18, 2026 at 02:54:29PM -0300, Leandro Ribeiro wrote:
> Before "drm/drm_blend: allow blend mode property without PREMULTI",
> userspace would have to assume that only PREMULTI was supported by
> drivers that didn't expose the blend mode property. But now userspace
> shouldn't relly on that, as they can't count with drivers always
> supporting PREMULTI.
>
> Error out if a driver expose alpha property or pixel formats with alpha
> and does not expose the blend mode property. This way userspace don't
> have to guess. Drivers that hit such error must be fixed.
>
> Signed-off-by: Leandro Ribeiro <[email protected]>
> ---
> drivers/gpu/drm/drm_crtc_internal.h | 2 +-
> drivers/gpu/drm/drm_drv.c | 7 ++++--
> drivers/gpu/drm/drm_mode_config.c | 37 +++++++++++++++++++++++++++--
> 3 files changed, 41 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc_internal.h
> b/drivers/gpu/drm/drm_crtc_internal.h
> index c09409229644..2a4862202496 100644
> --- a/drivers/gpu/drm/drm_crtc_internal.h
> +++ b/drivers/gpu/drm/drm_crtc_internal.h
> @@ -95,7 +95,7 @@ int drm_mode_setcrtc(struct drm_device *dev,
> /* drm_mode_config.c */
> int drm_modeset_register_all(struct drm_device *dev);
> void drm_modeset_unregister_all(struct drm_device *dev);
> -void drm_mode_config_validate(struct drm_device *dev);
> +int drm_mode_config_validate(struct drm_device *dev);
>
> /* drm_modes.c */
> const char *drm_get_mode_status_name(enum drm_mode_status status);
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 985c283cf59f..def78046a963 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -1059,8 +1059,11 @@ int drm_dev_register(struct drm_device *dev, unsigned
> long flags)
> const struct drm_driver *driver = dev->driver;
> int ret;
>
> - if (!driver->load)
> - drm_mode_config_validate(dev);
> + if (!driver->load) {
> + ret = drm_mode_config_validate(dev);
> + if (ret)
> + return ret;
> + }
>
> WARN_ON(!dev->managed.final_kfree);
>
> diff --git a/drivers/gpu/drm/drm_mode_config.c
> b/drivers/gpu/drm/drm_mode_config.c
> index 66f7dc37b597..18c6b5707532 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -674,16 +674,45 @@ static void validate_encoder_possible_crtcs(struct
> drm_encoder *encoder)
> encoder->possible_crtcs, crtc_mask);
> }
>
> -void drm_mode_config_validate(struct drm_device *dev)
> +static int plane_alpha_require_blend_mode(struct drm_plane *plane)
> +{
> + struct drm_device *dev = plane->dev;
> + const struct drm_format_info *fmt;
> + u32 i;
> +
> + /* blend mode property supported, no need to check anything */
> + if (plane->blend_mode_property)
> + return 0;
> +
> + if (plane->alpha_property) {
> + drm_err(dev, "[PLANE:%d:%s] alpha property exposed but blend
> mode not setup",
> + plane->base.id, plane->name);
> + return -EINVAL;
> + }
Why this? I don't think the constant alpha property has anything
really to do with the per-pixel alpha stuff.
> +
> + for (i = 0; i < plane->format_count; i++) {
> + fmt = drm_format_info(plane->format_types[i]);
> + if (fmt->has_alpha) {
> + drm_err(dev, "[PLANE:%d:%s] pixel format with alpha
> exposed but blend mode not setup",
> + plane->base.id, plane->name);
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> +}
> +
> +int drm_mode_config_validate(struct drm_device *dev)
> {
> struct drm_encoder *encoder;
> struct drm_crtc *crtc;
> struct drm_plane *plane;
> u32 primary_with_crtc = 0, cursor_with_crtc = 0;
> unsigned int num_primary = 0;
> + int ret = 0;
>
> if (!drm_core_check_feature(dev, DRIVER_MODESET))
> - return;
> + return ret;
>
> drm_for_each_encoder(encoder, dev)
> fixup_encoder_possible_clones(encoder);
> @@ -732,9 +761,13 @@ void drm_mode_config_validate(struct drm_device *dev)
> drm_for_each_plane(plane, dev) {
> if (plane->type == DRM_PLANE_TYPE_PRIMARY)
> num_primary++;
> +
> + ret |= plane_alpha_require_blend_mode(plane);
> }
>
> WARN(num_primary != dev->mode_config.num_crtc,
> "Must have as many primary planes as there are CRTCs, but have %u
> primary planes and %u CRTCs",
> num_primary, dev->mode_config.num_crtc);
> +
> + return ret;
> }
> --
> 2.54.0
--
Ville Syrjälä
Intel
