[igt-dev] [PATCH i-g-t 2/3] tests/kms_setmode: Request the initial vbl count with RELATIVE instead of ABSOLUTE

[Daniel Vetter]

On Tue, Nov 06, 2018 at 04:38:48PM +0000, Chris Wilson wrote:
> Quoting Ville Syrjala (2018-11-06 16:19:42)
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Asking for the initial vblank count by specifying and absolute vblank count of 0
> > doesn't make much sense. Switch to a relative query instead.
> > 
> > It doesn't look like we care about lining up on the first vblank boundary so
> > we can just drop the NEXTONMISS flag. Only the relative timestamps of the
> > events will matter.
> 
> I had to do a double take as quite often we care about submitting the
> workload before the next vblank, but no you are quite correct in this
> case so long as the next request is submitted within the next frame it
> should be fine and not miss a response.
> 
> To catch the error during setup, we could do something like
> 
> 	for (n = 0; n < CALIBRATE_TS_STEPS; n++) {
> 		drmVBlank check;
> 
> 		++wait.request.sequence;
> 		do_or_die(drmWaitVBlank(drm_fd, &wait));
> 
> 		/* Double check that haven't already missed the vblank */
> 		memset(&check, 0, sizeof(check));
> 		check.request.type = kmstest_get_vblank_flag(crtc_idx);
> 		check.request.type |= DRM_VBLANK_RELATIVE;
> 		do_or_die(drmWaitVBlank(drm_fd, &check));
> 
> 		igt_assert(!vblank_after(check.reply.sequence, wait.request.sequence));
> 	}
> 
> > 
> > v2: Drop the NEXTONMISS (Daniel)

I have no recollection of this, but comparing with
drm_wait_vblank_is_query() in the kernel this checks out. Also

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

on both.
-Daniel

> > 
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> For both, but do consider the value of checking our setup.
> -Chris

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch