Measurements: Massive Display-related power savings

Klaus Kurzmann mok at
Tue Oct 28 08:18:02 CET 2008

* Harald Welte <laforge at> [081028 07:11]:
> Hi all,

> On Wed, Oct 15, 2008 at 01:48:26PM +0200, Michael 'Mickey' Lauer wrote:
> > Am Wednesday 15 October 2008 06:38:01 schrieb Mike (mwester):
> > > > FSO should switch the backlight control from the sysfs method to the
> > > > fbdev-ioctl method.  It's backwards compatible to old kernels (which will
> > > > just backlight-blank) and future-compatible with kernels that add the
> > > > jbt6k74 notifier and glamo fb_blank() patches.
> > 
> > Already done, thanks to a patch from Harald and some refactoring.
> > While doing this, I encountered a strange thing. One of my FreeRunners does 
> > not recover from a BLANK ioctl anymore. The backlight turns on but the 
> > display does not show any pixels. I have to reboot to make it work again. 
> > Could that be connected to that infamous WSOD resume bug?

> After a bit of debugging today on mickeys phone, it seems like the jbt6k74
> fb_blank notifier is not to blame.  the display still comes up white after
> fb_blank ioctl was issued.

> The real problem is in glamofb_blank() code (which I have written
> as part of the patchset regarding the measurements in this thread).

> All that we do in glamofb_blank() is to disable DCLK of the display
> controller.  If I uncomment this code, the device properly comes back after
> the blanking.
Hmm, this is strange... If I disable disabling the DCLK, in
glamofb_blank() the device still comes back with a WSoD after
unblanking. If I disable entering deep-standby in fb_notifier_callback()
instead it comes back fine.

> It really puzzles me what could be the cause of this.  Only few GTA02 devices
> seem to show this behaviour.  Mickey's device exhibiting this problem is
> a MP GTA02v6, just like other devices not exhibiting the problem.  It is always
> reliable on a given device.  Either it does always come back with a white screen,
> or it does always work.  So it's unlikely timing related.
I can unblank it fine from deep-standby, if I do it within the first
minute after entering deep-standby... Afterwards I get a WSoD. Same with
resume - I could resume fine within the first minute after suspend, but
not afterwards... 


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