Re: warnings from validate_blend_mode_for_alpha_formats() in next-20260715

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Aug 26, 2026 at 02:28:15AM +0500, Mikhail Gavrilov wrote:
> Hi,
> 
> this is not a linux-next-only issue any more: 860e748bddcc came in with the
> drm-next pull of the 7.3 merge window, so it now warns on plain mainline. Here
> it fires 16 times on every boot - 8 per GPU, on the 4 primary and 4 cursor
> planes of each of the two cards in this machine:
> 
>   [PLANE:44:plane-0] pixel format with alpha exposed but blend mode not setup
>   WARNING: drivers/gpu/drm/drm_mode_config.c:872 at drm_mode_config_validate+0xa16/0x13b0
> 
> I ran into it on 7.2.0-2709dd5ae32f, bisected it to 860e748bddcc and confirmed
> by reverting that commit, before I found this thread. Hardware:
> 0000:03:00.0 Navi 31 (DCN 3.2) and 0000:0f:00.0 Raphael iGPU (DCN 3.1.5).
> 
> Nobody has put this on regzbot yet, so:
> 
> #regzbot introduced: 860e748bddcc
> #regzbot title: drm: WARNING at drm_mode_config_validate() for planes exposing alpha without a blend mode property
> #regzbot monitor: https://lore.kernel.org/all/20260813143605.106104-1-mwen@igalia.com/
> 
> Status as far as I can see it: Melissa Wen's v3 series (monitored above) fixes
> amdgpu for both DCN and DCE, has Reviewed-by from Alex Hung and Tested-by from
> Daniel Wheeler, and I tested it here too - the warnings are gone on both GPUs.
> It is in neither linux-next nor amd-staging-drm-next so far. 271e90eb5f9f
> ("drm: use drm_warn() in validate_blend_mode_for_alpha_formats()") turns the
> splat into a plain warning and went to drm-next on 2026-08-20 as part of
> drm-misc-next-fixes-2026-08-20, but has not reached mainline either. Other
> drivers are being fixed in separate threads (imx dcss, rockchip, vkms).
> 
> Since this was introduced during the 7.3 merge window, the fixes should land
> in 7.3 rather than wait for the next one.

I can confirm this regression.  It's hitting me here too on Linus's
latest tree.  It's not good to boot and have a bunch of warnings already
happening, resulting in a "tainted" kernel before I have the chance to
break anything manually myself...

thanks,

greg k-h