On 5/22/26 3:24 PM, Ville Syrjälä wrote:
> 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.
You’re right: if the pixel format has no alpha channel, the constant
alpha property produces identical results for COVERAGE and PREMULTI.
>
>> +
>> + 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
>
--
Leandro Ribeiro
