[PATCH] drm_modes: calculate nominal vrefresh in drm_display_mode_from_videomode

[Daniel Vetter]

On Thu, Dec 03, 2015 at 12:09:24PM +0100, Philipp Zabel wrote:
> Am Donnerstag, den 03.12.2015, 11:22 +0100 schrieb Thierry Reding:
> > On Thu, Dec 03, 2015 at 10:50:07AM +0100, Daniel Vetter wrote:
> > > On Thu, Dec 03, 2015 at 09:55:44AM +0100, Philipp Zabel wrote:
> > > > Use drm_mode_vrefresh to update the vrefresh field after changing the
> > > > modes' timings and flags.
> > > > 
> > > > Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
> > > > ---
> > > >  drivers/gpu/drm/drm_modes.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> > > > index cd74a09..b624be8 100644
> > > > --- a/drivers/gpu/drm/drm_modes.c
> > > > +++ b/drivers/gpu/drm/drm_modes.c
> > > > @@ -611,6 +611,8 @@ void drm_display_mode_from_videomode(const struct videomode *vm,
> > > >  		dmode->flags |= DRM_MODE_FLAG_DBLSCAN;
> > > >  	if (vm->flags & DISPLAY_FLAGS_DOUBLECLK)
> > > >  		dmode->flags |= DRM_MODE_FLAG_DBLCLK;
> > > > +	dmode->vrefresh = 0;
> > > 
> > > Rendundant. Or I'm blind.
> > 
> > Unfortunately it isn't.  drm_mode_vrefresh() is somewhat odd in that
> > it'll return the existing mode->vrefresh if it is > 0. I'm thinking that
> > perhaps it'd be useful to factor out the computation code into a
> > separate function, say drm_mode_calc_vrefresh(), and use that where you
> > really want to compute the value and at the same time use it to simplify
> > drm_mode_vrefresh() as well.
> 
> I don't understand the intention behind the drm_mode_vrefresh (and
> drm_mode_hsync) functions, but replacing all instances of
> 
>   mode->vrefresh = drm_mode_vrefresh(mode)
> 
> with something that always calculates the vrefresh sounds like a good
> idea to me.

Premature micro-optimization to avoid recomputing hrefresh/vrefresh all
the time I think. I'd drop this, and then redo your patch on top to also
drop the = 0 assignment.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch