Messages in this thread |  | | Date | Tue, 5 May 2026 10:14:33 -0300 | | Subject | Re: [PATCH v2 2/2] drm: ensure blend mode supported if alpha exposed | | From | Leandro Ribeiro <> |
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On 5/5/26 4:57 AM, Jani Nikula wrote: > On Mon, 04 May 2026, Leandro Ribeiro <leandro.ribeiro@collabora.com> 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 <leandro.ribeiro@collabora.com> >> --- >> 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. >
Yes, the function name choice wasn't good.
drm_mode_config_validate() only produces warnings, while drm_mode_config_enforce() returns error codes and should be used to prevent initializing a driver that does not comply with the required rules. In this case, the rule being added is supporting plane alpha but not the blend mode property.
I could add such kind of rule to drm_mode_config_validate() itself, but I wasn't sure if people would be happy with it producing both warnings and errors. But maybe that would be a better approach than what I did.
> >> + 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; >> +} >
-- Leandro Ribeiro
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