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

[Chris Wilson]

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)
> 
> 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