[PATCH] drm/amd/display: fix 64 bit divide in freesync code

[Alex Deucher]

On Thu, Apr 7, 2022 at 7:31 PM Nathan Chancellor <nathan at kernel.org> wrote:
>
> On Thu, Apr 07, 2022 at 03:50:29PM -0400, Alex Deucher wrote:
> > Use do_div() rather than a a 64 bit divide.
> >
> > Fixes: 3fe5739db48843 ("drm/amd/display: Add flip interval workaround")
> > Reported-by: kernel test robot <lkp at intel.com>
> > Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> > Cc: Angus Wang <Angus.Wang at amd.com>
> > Cc: Anthony Koo <Anthony.Koo at amd.com>
> > Cc: Aric Cyr <Aric.Cyr at amd.com>
> > ---
> >  drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> > index 0130f1879116..70f06fa8cc2b 100644
> > --- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> > +++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> > @@ -1230,6 +1230,7 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
> >  {
> >       struct core_freesync *core_freesync = NULL;
> >       unsigned int cur_timestamp_in_us;
> > +     unsigned long long tmp;
> >
> >       if ((mod_freesync == NULL) || (stream == NULL) || (in_out_vrr == NULL))
> >               return;
> > @@ -1239,7 +1240,9 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
> >       if (in_out_vrr->supported == false)
> >               return;
> >
> > -     cur_timestamp_in_us = dm_get_timestamp(core_freesync->dc->ctx)/10;
> > +     tmp = dm_get_timestamp(core_freesync->dc->ctx);
> > +     do_div(tmp, 10);
> > +     cur_timestamp_in_us = tmp;
>
> Any reason not to use
>
> cur_timestamp_in_us = div_u64(dm_get_timestamp(core_freesync->dc->ctx), 10)
>
> and save a variable?

I can do that.

Alex

>
> >       in_out_vrr->flip_interval.vsyncs_between_flip++;
> >       in_out_vrr->flip_interval.v_update_timestamp_in_us = cur_timestamp_in_us;
> > --
> > 2.35.1
> >
> >