Measurements: Massive Display-related power savings

[Klaus Kurzmann]

* Harald Welte <laforge at openmoko.org> [081017 12:30]:
> On Wed, Oct 15, 2008 at 04:21:38PM +0200, Klaus Kurzmann wrote:
> > * Michael 'Mickey' Lauer <mickey at openmoko.org> [081015 14:22]:
> > > 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?
> > I think so. I get a WSoD on every resume, when suspended for more than a
> > minute. And since the frameworkd uses the new fb for blanking the screen
> > I get it on un-blanking as well.
> > 
> > If I comment out the changes in fb_notifier_callback (jbt6k74.c) the
> > WSoD goes away...

> This seems like the jbt6k74 switch from deep-standby to sleep to normal is not
> working like it should.  Can you try using the sysfs nodes (echo "normal" or
> "deep-standby" or "sleep" > state) and see what happens?
0022 SU:root at om-gta02[pts/3]:~-> cat /sys/bus/spi/drivers/jbt6k74/spi2.0/state
normal
0022 SU:root at om-gta02[pts/3]:~-> echo -n "sleep" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state
[display gets white]
0022 SU:root at om-gta02[pts/3]:~-> echo -n "normal" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state
[display back again]
0022 SU:root at om-gta02[pts/3]:~-> echo -n "deep-standby" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state
[display gets white]
0022 SU:root at om-gta02[pts/3]:~-> echo -n "normal" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state      
[display back again]

BUT...

0022 SU:root at om-gta02[pts/3]:~-> echo -n "sleep" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state
[display gets white ... wait some time]
0022 SU:root at om-gta02[pts/3]:~-> echo -n "normal" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state
[display back again]
0022 SU:root at om-gta02[pts/3]:~-> echo -n "deep-standby" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state
[display gets white ... wait some time]                    
0022 SU:root at om-gta02[pts/3]:~-> echo -n "normal" > /sys/bus/spi/drivers/jbt6k74/spi2.0/state      
[display is still white and won't come back until reboot]

So it looks like WSoD comes after some time in deep-standby state.

> The timing values we got from the LCM vendor were _really_ crappy and we used
> to have this problem ages ago with GTA01.  When I complained that the modules
> were out of spec, the LCM vendor just sent an updated data sheet with more
> sloppy (slower) timings.  I altered the code and it worked on all the devices
> that I had access to.

> Maybe the SPI timings are now even lower.  You might want to try that.
What do I have to do?

Thanks
Mok