Measurements: Massive Display-related power savings

Harald Welte laforge at
Tue Oct 28 00:15:29 CET 2008

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.

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.

There would be two questions for Smedia (who's the contact inside Openmoko to
talk to them?):

1) Is there a certain condition when we can disable DCLK?  Maybe stopping
   this clock is only valid in a certain state e.g. during vertical blank?
   What we want to do is to stop the glamo from producing any video output

2) Did Openmoko ever use different silicon revisions of the Glamo 3362 for
   different production runs?

- Harald Welte <laforge at>         
Software for the world's first truly open Free Software mobile phone

More information about the openmoko-kernel mailing list