Re: [PATCH 2/3] drm: Make drm_mode_vrefresh() a bit more accurate

Ville Syrjälä
2018-03-14T14:50:30Z

On Wed, Mar 14, 2018 at 02:56:28PM +0100, Daniel Vetter wrote:
> On Tue, Mar 13, 2018 at 05:07:58PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Do the refresh rate calculation with a single division. This gives
> > us slightly more accurate results, especially for interlaced since
> > we don't just double the final truncated result.
> >
> > We do lose one bit compared to the old way, so with an interlaced
> > mode the new code can only handle ~2GHz instead of the ~4GHz the
> > old code handeled.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> I kinda want special integers here that Oops on overflow, I thought
> they're coming.

Would be nice indeed.

> That aside:
>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > ---
> > drivers/gpu/drm/drm_modes.c | 19 +++++++++----------
> > 1 file changed, 9 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> > index 4157250140b0..f6b7c0e36a1a 100644
> > --- a/drivers/gpu/drm/drm_modes.c
> > +++ b/drivers/gpu/drm/drm_modes.c
> > @@ -773,24 +773,23 @@ EXPORT_SYMBOL(drm_mode_hsync);
> > int drm_mode_vrefresh(const struct drm_display_mode *mode)
> > {
> > int refresh = 0;
> > - unsigned int calc_val;
> >
> > if (mode->vrefresh > 0)
> > refresh = mode->vrefresh;
> > else if (mode->htotal > 0 && mode->vtotal > 0) {
> > - int vtotal;
> > - vtotal = mode->vtotal;
> > - /* work out vrefresh the value will be x1000 */
> > - calc_val = (mode->clock * 1000);
> > - calc_val /= mode->htotal;
> > - refresh = (calc_val + vtotal / 2) / vtotal;
> > + unsigned int num, den;
> > +
> > + num = mode->clock * 1000;
> > + den = mode->htotal * mode->vtotal;
> >
> > if (mode->flags & DRM_MODE_FLAG_INTERLACE)
> > - refresh *= 2;
> > + num *= 2;
> > if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
> > - refresh /= 2;
> > + den *= 2;
> > if (mode->vscan > 1)
> > - refresh /= mode->vscan;
> > + den *= mode->vscan;
> > +
> > + refresh = DIV_ROUND_CLOSEST(num, den);
> > }
> > return refresh;
> > }
> > --
> > 2.16.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

--
Ville Syrjälä
Intel OTC
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