2012/5/23 Sean Paul <seanpaul at chromium.org>: > On Tue, May 22, 2012 at 6:15 PM, Zdenek Kabelac > <zdenek.kabelac at gmail.com> wrote: >> 2012/5/22 Zdenek Kabelac <zdenek.kabelac at gmail.com>: >>> 2012/5/22 Daniel Vetter <daniel at ffwll.ch>: >>>> On Tue, May 22, 2012 at 04:36:30PM +0200, Zdenek Kabelac wrote: >>>>> 2012/5/22 Daniel Vetter <daniel at ffwll.ch>: >>>>> > On Tue, May 22, 2012 at 02:08:46PM +0200, Zdenek Kabelac wrote: >>>>> >> Hi >>>>> >> >>>>> >> I've updated to 3.4 kernel, and now I'm noticing slight changes in >>>>> >> brightness on colorful images. >>>>> >> It seems the change is mostly visibly on ?'darker' images i.e. it's >>>>> >> not really visible on white background. >>>>> >> >>>>> >> When I reboot back to 3.3 ?kernel - brightness changes are gone - so I >>>>> >> do not suspect hw fault of my T61 display. >>>>> >> I guess once in past there has been already such bug, so this problem >>>>> >> seems to me like reintroducing the same >>>>> >> problem again. >>>>> >> >>>>> >> xorg-x11-server-Xorg-1.12.1-1.fc18.x86_64 >>>>> >> with SNA intel driver build from git repo. >>>>> >> T61, 965GM >>>>> >> >>>>> >> Is this a know issue ? >>>>> >> Is bisect needed ? >>>>> > >>>>> > You're the first one to report things, so a bisect would be highly >>>>> > appreciated. Also I'm a bit confused about what you mean by 'changing >>>>> > brightness'. Can you please try to explain this a bit more? >>>>> > >>>>> >>>>> I've some default gnome picture like this one: >>>>> https://lh6.googleusercontent.com/-96ZhFbfLX_M/ThHsm0ZxBgI/AAAAAAAAFQQ/3ApjzYgulso/s400/gnome-3-login-screen.png >>>>> >>>>> When I watch the picture for some period of time ?I'm noticing slight >>>>> changes in the picture brightness looking like small change in LUT >>>>> table or something like that. >>>>> If the picture is white I'm not noticing any change. >>>>> (Initially I've thought my display dies - but reboot to 3.3 fixed the >>>>> issue immediately). >>>> >>>> "for some period", does that mean it takes you a while to notice the >>>> changes (because they're tiny), or are the changes happend just rather slowly? >>>> >>> >>> Deviation in picture is not huge - but gets noticeable by my eyes and >>> it's annoying, >>> it's like several seconds between each minor change. >>> >>> If I've monotone background in i.e. text editor ?the change is >>> practically not visibible, >>> but if watch some digicam photos full screen they are quite obvious. >>> >>> Not sure if that has any influence (not tested without) ?I'm using >>> some icc profile >>> ('xcalib') to get away from blue of IBM display. >>> >>>>> Is there any suspecting patch for this chipset I should try to revert ? >>>> >>>> Tbh I have no idea. If there's no changes when the picture is white, it >>>> can't be the backlight, we haven't frobbed around with the gamma stuff and >>>> temporal dithering is disabled, too. If you can bisect this it would >>>> greatly help. >>> >>> ok, I'll play this game in the evening if there is nothing obvious. >>> >> >> And we have a winner - cec2f356d59d9e070413e5966a3c5a1af136d948 >> > > Hmm, seems like your display doesn't like to be downclocked, or rather > you don't like it to be downclocked :) The reason this patch triggered > it is because it does a better job of finding a compatible clock. You > can disable lvds downclocking on the kernel command line by setting > i915.lvds_downclock=0 > 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 ? Zdenek
