Re: [PATCH v2] drm/pl111: drop alpha formats the hardware cannot scan out

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The patch fails to remove alpha pixel formats from board-specific variant tables in `pl111_versatile.c` (such as `pl111_realview_pixel_formats` used by `vexpress-a15`). This leaves the original bug unfixed on the exact platform mentioned in the commit message. Furthermore, it introduces a new regression: because the alpha case labels were removed from `pl111_display_enable()`, selecting one of these still-exposed formats will hit the `default:` case. This triggers a new `WARN_ONCE` and fails to properly configure the hardware display registers (skipping `cntl` setup).
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commit 10499c458facc30bed43b7322f9a6352b1c136f7
Author: Roshan Kumar <roshaen09@gmail.com>

drm/pl111: drop alpha formats the hardware cannot scan out

This commit removes alpha pixel formats from the PL110 and PL111 variant
tables to prevent exposing unsupported blend modes to userspace. It also
removes the corresponding format case labels from the display setup code.

Link: https://github.com/google/syzkaller/issues/7805

> diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
> index 5d10bc5fdf1f6..e1b513d36c27c 100644
> --- a/drivers/gpu/drm/pl111/pl111_display.c
> +++ b/drivers/gpu/drm/pl111/pl111_display.c
> @@ -267,14 +267,12 @@ static void pl111_display_enable(struct drm_simple_display_pipe *pipe,
>  		if (priv->variant->st_bitmux_control)
>  			cntl |= CNTL_ST_LCDBPP24_PACKED;
>  		break;
> -	case DRM_FORMAT_ABGR8888:
>  	case DRM_FORMAT_XBGR8888:

[Severity: High]
Will removing these case labels cause a regression for boards using the
versatile variants?

It looks like the alpha formats were not removed from the board-specific
tables in drivers/gpu/drm/pl111/pl111_versatile.c (such as the
pl111_realview_pixel_formats table used by vexpress-a15).

Because those formats are still exposed to userspace, if an application
selects an alpha format like DRM_FORMAT_ABGR8888, pl111_display_enable()
will now fall through to the default case:

    default:
        WARN_ONCE(true, "Unknown FB format 0x%08x\n",
                  fb->format->format);
        break;

This seems like it would trigger the newly reachable warning (causing boot
failures on systems like the vexpress-a15 manager if panic_on_warn is
enabled) and fail to properly configure the hardware display registers.
Should the versatile formats be updated to drop the alpha formats as well?

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260910054503.4155812-1-roshaen09@gmail.com?part=1