2012/5/23 Daniel Vetter <daniel at ffwll.ch>: > On Wed, May 23, 2012 at 01:48:41PM +0200, Zdenek Kabelac wrote: >> 2012/5/23 Daniel Vetter <daniel at ffwll.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) > > Hm, that sounds more like something ugly is happening when we switch > frequencies as opposed to the different frequency causing interference > with the backlight. Just to check: You only see a quick flash, then > brightness is back to normal? In fact I'm not really noticing the moment it goes back to normal - I'll notice when it gets darker. i.e. when I open picture with 'qiv' - after a second I notice that picture becomes a bit darker. If I do not move with anything - it stays this way. > > If that's the case, please try Chris' fastboot branch. vsyncing the > frequency change might indeed fix this. > I've tried to compile, but compilation finished with some errors - so I've tried to rebase branch on master 3.4 - tried to resolve some error - but probably in a wrong thus resulted kernel given me just black screen when X has been initialized. So I'll try to remove some config options and I'll try to rebuild original fastboot branch later. Zdenek
