linux-kernel - Re: [PATCH v6 01/11] drm/fourcc: Add warning for bad bpp

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Message-ID: <vj3budjobsehi3hl2mcmondt2f4giups6cxeiraeo2ensgw3du@smxivopyzfez>
Date: Thu, 2 Oct 2025 08:52:02 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Vishal Sagar <vishal.sagar@....com>,
        Anatoliy Klymenko <anatoliy.klymenko@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Michal Simek <michal.simek@....com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Pekka Paalanen <ppaalanen@...il.com>
Subject: Re: [PATCH v6 01/11] drm/fourcc: Add warning for bad bpp

On Wed, Oct 01, 2025 at 04:22:13PM +0300, Tomi Valkeinen wrote:
> drm_format_info_bpp() cannot be used for formats which do not have an
> integer bits-per-pixel in a pixel block.
> 
> E.g. DRM_FORMAT_XV15's (not yet in upstream) plane 0 has three 10-bit
> pixels (Y components), and two padding bits, in a 4 byte block. That is
> 10.666... bits per pixel when considering the whole 4 byte block, which
> is what drm_format_info_bpp() does. Thus a driver that supports such
> formats cannot use drm_format_info_bpp(),
> 
> It is a driver bug if this happens, but so handle wrong calls by
> printing a warning and returning 0.
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> ---
>  drivers/gpu/drm/drm_fourcc.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>


-- 
With best wishes
Dmitry