[PATCH] drm/radeon: Prefer lower feedback dividers

[Alex Deucher]

Applied.  Thanks!

Alex

On Thu, Aug 27, 2020 at 7:18 AM Christian König
<christian.koenig at amd.com> wrote:
>
> Am 25.08.20 um 19:33 schrieb Kai-Heng Feng:
> > Commit 2e26ccb119bd ("drm/radeon: prefer lower reference dividers")
> > fixed screen flicker for HP Compaq nx9420 but breaks other laptops like
> > Asus X50SL.
> >
> > Turns out we also need to favor lower feedback dividers.
>
> Mhm, let's hope that this works out for all others as well :)
>
> >
> > Users confirmed this change fixes the regression and doesn't regress the
> > original fix.
> >
> > Fixes: 2e26ccb119bd ("drm/radeon: prefer lower reference dividers")
> > BugLink: https://bugs.launchpad.net/bugs/1791312
> > BugLink: https://bugs.launchpad.net/bugs/1861554
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
>
> Reviewed-by: Christian König <christian.koenig at amd.com>
>
> > ---
> >   drivers/gpu/drm/radeon/radeon_display.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
> > index e0ae911ef427..7b69d6dfe44a 100644
> > --- a/drivers/gpu/drm/radeon/radeon_display.c
> > +++ b/drivers/gpu/drm/radeon/radeon_display.c
> > @@ -933,7 +933,7 @@ static void avivo_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_div,
> >
> >       /* get matching reference and feedback divider */
> >       *ref_div = min(max(den/post_div, 1u), ref_div_max);
> > -     *fb_div = DIV_ROUND_CLOSEST(nom * *ref_div * post_div, den);
> > +     *fb_div = max(nom * *ref_div * post_div / den, 1u);
> >
> >       /* limit fb divider to its maximum */
> >       if (*fb_div > fb_div_max) {
>
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