linux-kernel - Re: [PATCH 03/21] drm/i915: Remove extra 300ms delay during eDP mode setting

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Message-ID: <20110930180959.GP2859@phenom.ffwll.local>
Date:	Fri, 30 Sep 2011 20:09:59 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Keith Packard <keithp@...thp.com>,
	Dave Airlie <airlied@...hat.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	"Barnes, Jesse" <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH 03/21] drm/i915: Remove extra 300ms delay during eDP mode
 setting

On Fri, Sep 30, 2011 at 07:58:21PM +0200, Daniel Vetter wrote:
> On Fri, Sep 30, 2011 at 10:50:10AM -0700, Keith Packard wrote:
> > On Fri, 30 Sep 2011 18:27:28 +0200, Daniel Vetter <daniel@...ll.ch> wrote:
> > 
> > > Can you elaborate a bit why this is no longer needed? Jesse seems to have
> > > introduced this spefically for edp panels in d209848d61794968. If this
> > > becomes rendundant due to your panel power sequencing fixes, maybe move it
> > > down the series?
> > 
> > The only reason for this delay is to avoid some potential noise on the
> > screen during mode setting, all of the power sequencing delays are
> > already correctly managed by the driver. As far as I can tell, we're
> > trading off the small potential for noise on the screen with an extra
> > 300ms delay at boot time.
> > 
> > In the eDP spec, there's a delay listed (T8) between the start of video
> > data and turning on the backlight. There are no values presented and
> > the instructions are simply that the source is supposed to wait until
> > the display is stable. I'm not sure how we'd ever know that the display
> > is stable.
> 
> Ok, maybe add the above to paragraphs to the commit msg. Then
> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

On further strolling through bspec to review later patches I've noticed
that PCH_PP_ON_DELAYS and PCH_PP_OFF_DELAYS seem to have values for
power on->backlight on and backlight off->panel off delays. Maybe we
should use these?
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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