Re: [PATCH] drm/modeset-helper: Add blend mode property to the legacy primary plane

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 02.09.26 um 05:12 schrieb oushixiong1025@163.com:
> From: Shixiong Ou <oushixiong@kylinos.cn>
>
> The primary plane created by drm_crtc_init() exposes ARGB8888, which
> has an alpha channel, but never gets a "pixel blend mode" property, so
> drm_mode_config_validate() warns for every driver using this helper
> (radeon, gma500, legacy amdgpu DCE). Advertise only
> DRM_MODE_BLEND_PREMULTI, the mode userspace always assumed when the
> property was absent.

I'd like to suggest a different strategy. The helper drm_crtc_init() is 
deprecated and there are only 3 drivers left that call it: amdgpu, 
gma500 and radeon.  It would be better to make a series for each that 
integrates the helper into the driver and adapts the format array to the 
hardware/driver's actual functionality. For gma500 at least, I'm pretty 
sure it does not support ARGB on its primary plane.

There's also work happening already for fixing amdgpu blend properties IIRC.

Best regards
Thomas

>
> Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
> ---
>   drivers/gpu/drm/drm_modeset_helper.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_modeset_helper.c b/drivers/gpu/drm/drm_modeset_helper.c
> index e54584da4c3d..4c59e82af2f1 100644
> --- a/drivers/gpu/drm/drm_modeset_helper.c
> +++ b/drivers/gpu/drm/drm_modeset_helper.c
> @@ -23,6 +23,7 @@
>   #include <linux/export.h>
>   
>   #include <drm/drm_atomic_helper.h>
> +#include <drm/drm_blend.h>
>   #include <drm/drm_client_event.h>
>   #include <drm/drm_fourcc.h>
>   #include <drm/drm_framebuffer.h>
> @@ -160,6 +161,17 @@ int drm_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
>   	 */
>   	primary->format_default = true;
>   
> +	/*
> +	 * safe_modeset_formats[] includes ARGB8888, which has an alpha
> +	 * channel. Advertise the blend mode userspace has always assumed
> +	 * for such planes when the "pixel blend mode" property was absent,
> +	 * to satisfy drm_mode_config_validate().
> +	 */
> +	ret = drm_plane_create_blend_mode_property(primary,
> +						   BIT(DRM_MODE_BLEND_PREMULTI));
> +	if (ret)
> +		goto err_drm_plane_cleanup;
> +
>   	ret = drm_crtc_init_with_planes(dev, crtc, primary, NULL, funcs, NULL);
>   	if (ret)
>   		goto err_drm_plane_cleanup;

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)