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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Nov 06, 2018 at 05:57:06PM +0100, Daniel Vetter wrote:
> 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@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

It's an oldie :) Spotted while trawling patchwork for ancient treasures.

> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> on both.
> -Daniel
> 
> > > 
> > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Reviewed-by: Chris Wilson <chris@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

-- 
Ville Syrjälä
Intel
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