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

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Date:	Wed, 23 May 2012 13:48:41 +0200
From:	Zdenek Kabelac <zdenek.kabelac@...il.com>
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

2012/5/23 Daniel Vetter <daniel@...ll.ch>:
> 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


Now when it's obvious it's related to powersaving  - it's probably
much easier to explain,
that I've been observing those changes when some activity was happing -
i.e. opening  picture - and after like 1 second image has flashed, -
then I've moved the mouse
stopped - and again image has flashed with brightness a bit.

The issue would be probably far less noticeable if the period of time
of idle GPU would have to be
much longer (i.e. in minute range)

Zdenek
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