RE: [PATCH 01/10] drm/fourcc: Add warning for bad bpp

[Sagar, Vishal]

[AMD Official Use Only - AMD Internal Distribution Only]

Hi Tomi

> -----Original Message-----
> From: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> Sent: Wednesday, December 18, 2024 12:49 PM
> To: Sagar, Vishal <vishal.sagar@xxxxxxx>
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; Klymenko, Anatoliy <Anatoliy.Klymenko@xxxxxxx>;
> Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>; Maxime Ripard
> <mripard@xxxxxxxxxx>; Thomas Zimmermann <tzimmermann@xxxxxxx>; David
> Airlie <airlied@xxxxxxxxx>; Simona Vetter <simona@xxxxxxxx>; Laurent Pinchart
> <laurent.pinchart@xxxxxxxxxxxxxxxx>; Simek, Michal <michal.simek@xxxxxxx>
> Subject: Re: [PATCH 01/10] drm/fourcc: Add warning for bad bpp
>
> Hi Vishal,
>
> On 04/12/2024 18:26, Sagar, Vishal wrote:
> > [AMD Official Use Only - AMD Internal Distribution Only]
> >
> > Hi Tomi,
> >
> > Thanks for the patch.
> >
> >> -----Original Message-----
> >> From: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> >> Sent: Wednesday, December 4, 2024 10:31 AM
> >> To: Sagar, Vishal <vishal.sagar@xxxxxxx>; Klymenko, Anatoliy
> >> <Anatoliy.Klymenko@xxxxxxx>; Maarten Lankhorst
> >> <maarten.lankhorst@xxxxxxxxxxxxxxx>; Maxime Ripard <mripard@xxxxxxxxxx>;
> >> Thomas Zimmermann <tzimmermann@xxxxxxx>; David Airlie
> >> <airlied@xxxxxxxxx>; Simona Vetter <simona@xxxxxxxx>; Laurent Pinchart
> >> <laurent.pinchart@xxxxxxxxxxxxxxxx>; Simek, Michal
> <michal.simek@xxxxxxx>
> >> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> >> kernel@xxxxxxxxxxxxxxxxxxx; Tomi Valkeinen
> <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> >> Subject: [PATCH 01/10] drm/fourcc: Add warning for bad bpp
> >>
> >> drm_format_info_bpp() cannot be used for formats which do not have an
> >> integer bits-per-pixel. Handle wrong calls by printing a warning and
> >> returning 0.
> >
> > It would be good to add an example of pixel format that may cause this issue.
>
> Indeed, the description is perhaps a bit lacking. I'll change it to:
>
> 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.
>

This looks good to me.

Vishal

>   Tomi
>
> >>
> >> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> >> ---
> >>   drivers/gpu/drm/drm_fourcc.c | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
> >> index 193cf8ed7912..e84c4ed6928c 100644
> >> --- a/drivers/gpu/drm/drm_fourcc.c
> >> +++ b/drivers/gpu/drm/drm_fourcc.c
> >> @@ -429,6 +429,13 @@ unsigned int drm_format_info_bpp(const struct
> >> drm_format_info *info, int plane)
> >>        if (!info || plane < 0 || plane >= info->num_planes)
> >>                return 0;
> >>
> >> +     if (info->char_per_block[plane] * 8 %
> >> +         (drm_format_info_block_width(info, plane) *
> >> +          drm_format_info_block_height(info, plane))) {
> >> +             pr_warn("unable to return an integer bpp\n");
> >> +             return 0;
> >> +     }
> >> +
> >>        return info->char_per_block[plane] * 8 /
> >>               (drm_format_info_block_width(info, plane) *
> >>                drm_format_info_block_height(info, plane));
> >>
> >> --
> >> 2.43.0
> >
> > Regards
> > Vishal Sagar