[Intel-gfx] [PATCH igt] igt/kms_flip: Calibrate timestamp errors

[Daniel Vetter]

On Mon, Oct 24, 2016 at 10:38:34AM +0100, Chris Wilson wrote:
> On Mon, Oct 24, 2016 at 11:14:31AM +0200, Daniel Vetter wrote:
> > On Mon, Oct 24, 2016 at 09:54:52AM +0100, Chris Wilson wrote:
> > Also with this patch we should be able to throw out the hacks for tv-out.
> > I only added those because the reported mode-timings are massively off
> > (due to the magic tv scaler thing) from the real timestamps we receive.
> > Auto-detecting this is much better.
> 
> Not quite just yet, we need to split the timing tests into a subgroup
> with a subtest per output so that we can skip one without skipping the
> others. At the moment, this check makes it bail out on my ctg/ilk who
> have a difference of about 50us between measured and expected vblank
> interval on LVDS (which is nigh on impossible given our confidence in the
> measurement, i.e. about 7 sigma).

Hm, should we be a bit more sloppy in our acceptance? Iirc Ville has made
changes to make it a bit more strict a while ago, and way, way back this
stuff worked on my ctg. Haven't fired it up in a while ;-)

> > And another issue: Failing to match the reported mode timings is a driver
> > bug.
> 
> Not quite, remember we override the user for fixed mode panels. But yes,
> piglit also has a similar expectation that the dotclock we report (via
> GetMscRate) in someway corresponds to actual vblank interval.

Yeah, I hope that DRRS would fix that, at least on newer stuff. At least I
proposed just using the matching dotclock for manual DRRS (mostly to
perfectly match with the refresh rate of a video). Didn't yet happen :(

But at least for the default mode we should try real hard to match.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch