linux-kernel - Re: Regression on GMA965 - display seems to have slow jump changes in brightness

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Message-ID: <20120523091109.GI5062@phenom.ffwll.local>
Date:	Wed, 23 May 2012 11:11:09 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Sean Paul <seanpaul@...omium.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	intel-gfx@...ts.freedesktop.org, jbarnes@...tuousgeek.org
Subject: Re: Regression on GMA965 - display seems to have slow jump changes
 in brightness

On Wed, May 23, 2012 at 09:07:28AM +0200, Daniel Vetter wrote:
> On Wed, May 23, 2012 at 08:59:07AM +0200, Zdenek Kabelac wrote:
> > Hmm I've been using i915.lvds_downclock=1 on grub command line, and
> > haven't noticed any visible problems with 3.3 kernel. So I'd rather
> > ask if the problematic patch isn't doing downclocking in a wrong way?
> > Or maybe detection that downclocking is not supported properly is not
> > correct now ?
> 
> Nope, Sean's analysis is pretty much correct, that patch only makes
> downclocking possible in more circumstances. And downclocking can
> certainly explain what you're seeing, the backlight pwm signal is driven
> off the panel dotclock, so if we change that we can very likely cause some
> funny interference. I guess we could frob the backligth control settings
> and adjust them for the change in clockspeed, but the current backlight
> code is a bit a mess. So right now I suggest you just drop that option -
> there are reasons it's not the default ;-)

Quick question: What's the frequency of the brightness change? And how
regular are the changes?
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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