linux-kernel - Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE

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Date:   Thu, 6 Jul 2017 20:59:40 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Keith Packard <keithp@...thp.com>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Airlie <airlied@...hat.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE
 ioctls

On Thu, Jul 06, 2017 at 09:28:40AM -0700, Keith Packard wrote:
> Ville Syrjälä <ville.syrjala@...ux.intel.com> writes:
> 
> > Maybe, or maybe we want to turn the interrupt on in that case? That's
> > what the old ioctl does.
> 
> That's what I suggested in my reply to Daniel's review. Even if we add
> the accurate function, we'll still need the interrupt-enable case as a
> fallback for drivers which don't support the accurate path, right?

TBH I didn't even consider that case, but yeah makes sense. Otherwise
the counter won't start to tick and the result of the query is pretty
much useless.

I was mostly thinking of the 'seq = query(); wait(seq + n);' pattern
where we can avoid doing the full update more than once if we enable
the interrupt already during the query.

-- 
Ville Syrjälä
Intel OTC