Re: [igt-dev] [PATCH i-g-t] igt/kms_flip: Allow reported vblank times to be in the future

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

On Thu, May 10, 2018 at 05:04:34PM +0100, Chris Wilson wrote:
> The vblank timestamp is given for the end of the vblank, but the
> hardware may report the vblank before that point (so the kernel computes
> a timestamp in the future), and userspace may then see the vblank event
> that says the actual start-of-scanout has yet to happen. All this is
> perfectly legal and can be observed in practice.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106087
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  tests/kms_flip.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/tests/kms_flip.c b/tests/kms_flip.c
> index 3d6fe948d..5b0d07cc2 100644
> --- a/tests/kms_flip.c
> +++ b/tests/kms_flip.c
> @@ -480,13 +480,6 @@ static void check_state(const struct test_output *o, const struct event_state *e
>  	if (es->count == 0)
>  		return;
>  
> -	timersub(&es->current_ts, &es->last_received_ts, &diff);
> -	igt_assert_f(timercmp(&es->last_received_ts, &es->current_ts, <),

last_received_ts is the time we received the previous event isn't it? So
somehow our current event's kernel reported timestamp is older than the
the time we received the previous event. So the kernel failed to send
events when it was supposed to, or we failed to process them in a timely
fashion perhaps?

> -		     "%s ts before the %s was issued!\n"
> -		     "timerdiff %ld.%06ld\n",
> -		     es->name, es->name,
> -		     diff.tv_sec, diff.tv_usec);
> -
>  	/* check only valid if no modeset happens in between, that increments by
>  	 * (1 << 23) on each step. This bounding matches the one in
>  	 * DRM_IOCTL_WAIT_VBLANK. */
> -- 
> 2.17.0
> 
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-- 
Ville Syrjälä
Intel
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