linux-kernel - Re: [Intel-gfx] [PATCH 9/9] drm/i915: Disable eDP VDD in a delayed work proc instead of synchronously

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Message-ID: <yunsjnqfqga.fsf@aiko.keithp.com>
Date:	Tue, 20 Sep 2011 21:51:33 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Dave Airlie <airlied@...hat.com>, intel-gfx@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 9/9] drm/i915: Disable eDP VDD in a delayed work proc instead of synchronously

On Wed, 21 Sep 2011 09:47:59 +0530, Jesse Barnes <jbarnes@...tuousgeek.org> wrote:

> I'm worried this makes our PPS even more complex and hard to follow.
> I'd rather see VDD AUX applied only when we need it (dpms, mode set and
> detect; for hotplug we can assume the panel is alive) and that we
> carefully disable it after waiting for a time after a full PPS on
> sequence when doing a mode set or dpms on command.

You'll see the fairly long list of places where VDD AUX is needed in my
other reply; a couple of them could probably be fixed by moving the PPS
calls around.

> Having all the power stuff at the highest levels would be clearest I
> think.

Yes, making it cleaner would help a ton. There are some basic problems
with the DRM API that make this hard though -- intel_dp_prepare may not
ever be followed by a call to intel_dp_commit. That's why I had the VDD
AUX stuff get turned off by a delayed work proc instead.

Also, leaving VDD AUX high after EDID is fetched means that we can start
the mode setting immediately, rather than having to wait for the
power-off/power-on delay (which is really long).

What we could do is force VDD AUX off after the panel gets turned on;
that would ensure that turning the panel off would actually turn the
power off, rather than having VDD stay high for some time after that.

-- 
keith.packard@...el.com

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