Re: [PATCH 1/7] drm: Fix drm_fixp2int_round() making it add 0.5

[Melissa Wen]

On 16/03/2024 08:59, Arthur Grillo wrote:
> On 12/03/24 15:27, Melissa Wen wrote:
> > On 03/06, Arthur Grillo wrote:
> > > As well noted by Pekka[1], the rounding of drm_fixp2int_round is wrong.
> > > To round a number, you need to add 0.5 to the number and floor that,
> > > drm_fixp2int_round() is adding 0.0000076. Make it add 0.5.
> > >
> > > [1]: https://lore.kernel.org/all/20240301135327.22efe0dd.pekka.paalanen@xxxxxxxxxxxxx/
> > Hi Arthur,
> >
> > thanks for addressing this issue.
> >
> > Please, add a fix tag to the commit that you are fixing, so we can
> > easily backport. Might be this commit:
> > https://cgit.freedesktop.org/drm/drm-misc/commit/drivers/gpu/drm/vkms?id=ab87f558dcfb2562c3497e89600dec798a446665
> Wouldn't be this commit instead?
> https://cgit.freedesktop.org/drm/drm-misc/commit/?id=8b25320887d7feac98875546ea0f521628b745bb
Yes, you're right!

Melissa
> Best Regards,
> ~Arthur Grillo
>
>
> > > Suggested-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
> > > Signed-off-by: Arthur Grillo <arthurgrillo@xxxxxxxxxx>
> > > ---
> > >   include/drm/drm_fixed.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
> > > index 0c9f917a4d4b..de3a79909ac9 100644
> > > --- a/include/drm/drm_fixed.h
> > > +++ b/include/drm/drm_fixed.h
> > > @@ -90,7 +90,7 @@ static inline int drm_fixp2int(s64 a)
> > >   
> > >   static inline int drm_fixp2int_round(s64 a)
> > >   {
> > > -	return drm_fixp2int(a + (1 << (DRM_FIXED_POINT_HALF - 1)));
> > Also, this is the only usage of DRM_FIXED_POINT_HALF. Can you also
> > remove it as it won't be used anymore?
> >
> > > +	return drm_fixp2int(a + DRM_FIXED_ONE / 2);
> > Would this division be equivalent to just shifting 1ULL by 31 instead of
> > 32 as done in DRM_FIXED_ONE?
> >
> > Melissa
> >
> > >   }
> > >   
> > >   static inline int drm_fixp2int_ceil(s64 a)
> > >
> > > --
> > > 2.43.0