On Mon, 04 May 2026, Leandro Ribeiro <[email protected]> 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 | 1 +
> drivers/gpu/drm/drm_drv.c | 7 ++++-
> drivers/gpu/drm/drm_mode_config.c | 42 +++++++++++++++++++++++++++++
> 3 files changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc_internal.h
> b/drivers/gpu/drm/drm_crtc_internal.h
> index c09409229644..bdbb6b9b94ea 100644
> --- a/drivers/gpu/drm/drm_crtc_internal.h
> +++ b/drivers/gpu/drm/drm_crtc_internal.h
> @@ -96,6 +96,7 @@ int drm_mode_setcrtc(struct drm_device *dev,
> 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_enforce(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..76766a370650 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -1059,9 +1059,14 @@ int drm_dev_register(struct drm_device *dev, unsigned
> long flags)
> const struct drm_driver *driver = dev->driver;
> int ret;
>
> - if (!driver->load)
> + if (!driver->load) {
> drm_mode_config_validate(dev);
>
> + ret = drm_mode_config_enforce(dev);
Reading the code, I'll have no idea what "enforce" means here. Reading
the function itself isn't helping either.
BR,
Jani.
> + if (ret)
> + return ret;
> + }
> +
> WARN_ON(!dev->managed.final_kfree);
>
> if (drm_dev_needs_global_mutex(dev))
> diff --git a/drivers/gpu/drm/drm_mode_config.c
> b/drivers/gpu/drm/drm_mode_config.c
> index 66f7dc37b597..20fd26ecb957 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -738,3 +738,45 @@ void drm_mode_config_validate(struct drm_device *dev)
> "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);
> }
> +
> +static int plane_require_blend_mode_for_alpha(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;
> + }
> +
> + 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_enforce(struct drm_device *dev)
> +{
> + struct drm_plane *plane;
> + int ret;
> +
> + drm_for_each_plane(plane, dev) {
> + ret = plane_require_blend_mode_for_alpha(plane);
> + if (ret)
> + return ret;
> + }
> +
> + return 0;
> +}
--
Jani Nikula, Intel
