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

Thierry Reding
2014-07-30T14:20:25Z

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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);
}

Then implement drm_wait_vblank() (or drm_wait_one_vblank()) on top of
that as a special case. Of course one could equally well implement
drm_wait_vblank_count() on top of your drm_wait_{one_,}vblank().

I couldn't think of a safe way to make the above work without the
loop...

Thierry

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