Re: [Intel-gfx] [PATCH 7/8] drm/irq: Implement a generic vblank_wait function

Ville Syrjälä
2014-07-30T14:36:21Z

On Wed, Jul 30, 2014 at 04:20:25PM +0200, Thierry Reding wrote:
> On Wed, Jul 30, 2014 at 05:32:28PM +0900, Michel Dänzer wrote:
> > On 30.07.2014 17:22, Daniel Vetter wrote:
> > > On Wed, Jul 30, 2014 at 11:59:33AM +0900, Michel Dänzer wrote:
> > >> On 30.07.2014 06:32, Daniel Vetter wrote:
> > >>> + * due to lack of driver support or because the crtc is off.
> > >>> + */
> > >>> +void drm_crtc_vblank_wait(struct drm_crtc *crtc)
> > >>> +{
> > >>> + drm_vblank_wait(crtc->dev, drm_crtc_index(crtc));
> > >>> +}
> > >>> +EXPORT_SYMBOL(drm_crtc_vblank_wait);
> > >>> +
> > >>> +/**
> > >>
> > >> Maybe the function names should be *_vblank_wait_next() or something to
> > >> clarify the purpose and reduce potential confusion versus drm_wait_vblank().
> > >
> > > Yeah that name is just transferred from the i915 driver. What about
> > > drm_wait_one_vblank()/drm_crtc_wait_one_vblank()?
> >
> > I don't care that much :), go ahead.
>
> Just my two cents: our downstream kernel has a helper somewhat like this
> which waits for a specified number of frames (apparently this is useful
> for some panels that require up to 5 or 6 frames before they display the
> correct image on screen). So perhaps something like this could work:
>
> void drm_wait_vblank_count(struct drm_device *dev, unsigned int crtc,
> unsigned int count)
> {
> u32 last;
> int ret;
>
> ret = drm_vblank_get(dev, crtc);
> if (WARN_ON(ret))
> return;
>
> while (count--) {
> last = drm_vblank_count(dev, crtc);
>
> ...
> }
>
> drm_vblank_put(dev, crtc);
> }

Would be nicer to wait for an absolute vblank count instead IMO. Or
if you want to pass a relative count in just convert it to an absolute
count first and wait for it (taking wraparound into account obviously).

--
Ville Syrjälä
Intel OTC