Re: [PATCH] drm/pl111: Advertise no pixel blending

[Thomas Zimmermann]

Hi

Am 25.08.26 um 12:54 schrieb Roshan Kumar:
> Commit 860e748bddcc ("drm: ensure blend mode supported if
> pixel format with alpha exposed") added validation that warns when a
> plane exposes an alpha format without a pixel blend mode property. PL111
> exposes several such formats but does not attach the property.
>
> The PL110/PL111 controller scans out a single framebuffer and does not
> blend its alpha channel with a background. Advertise
> DRM_MODE_BLEND_PIXEL_NONE to match the existing hardware behavior.

Why does the driver report ARGB formats in the first place. I'm looking 
at the code at [1] and I don't see any difference to XRGB. Unless I'm 
missing something, please remove ARGB formats from this driver instead. 
Drivers should not report formats they don't support.

[1] 
https://elixir.bootlin.com/linux/v7.2.2/source/drivers/gpu/drm/pl111/pl111_display.c#L259

Best regards
Thomas

> With panic_on_warn enabled, this warning prevents the syzkaller
> vexpress-a15 manager from booting. The change was tested on current
> master with QEMU 10 and the existing production DTB; the guest reached
> sshd and returned an SSH banner.
>
> Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> Link: https://github.com/google/syzkaller/issues/7805
> Signed-off-by: Roshan Kumar <roshaen09@xxxxxxxxx>
> ---
>   drivers/gpu/drm/pl111/pl111_display.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
> index 5d10bc5..758b297 100644
> --- a/drivers/gpu/drm/pl111/pl111_display.c
> +++ b/drivers/gpu/drm/pl111/pl111_display.c
> @@ -15,6 +15,7 @@
>   #include <linux/media-bus-format.h>
>   #include <linux/of_graph.h>
>   
> +#include <drm/drm_blend.h>
>   #include <drm/drm_fb_dma_helper.h>
>   #include <drm/drm_fourcc.h>
>   #include <drm/drm_framebuffer.h>
> @@ -596,5 +597,10 @@ int pl111_display_init(struct drm_device *drm)
>   	if (ret)
>   		return ret;
>   
> +	ret = drm_plane_create_blend_mode_property(&priv->pipe.plane,
> +						   BIT(DRM_MODE_BLEND_PIXEL_NONE));
> +	if (ret)
> +		return ret;
> +
>   	return 0;
>   }

--
--
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)