[Intel-gfx] [PATCH] add LVDS downclocking support

[Steven J Newbury]

On Sun, 2009-03-22 at 20:18 +0100, Erik Andrén wrote:
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> 
> Jesse Barnes wrote:
> > This is a refreshed patch from Matthew Garrett to enable LVDS downclocking.
> > 965+ hardware can do this automatically, but other 9xx chips need some help. 
> > So this patch adds some damage code to track idle time.  If we're idle for
> > more than 500ms we downclock the display based on the value calculated at
> > mode set time.
> > 
> > Comments & testing appreciated.  I've only tested on my GM45 so far, and I
> > think to fully realize the benefits we'll need to enable self refresh, but it
> > should help on many platforms as-is.
> > 
> 
> Hi,
> I've tested this on my 965GM laptop applied on top of Ubuntu Jauntys
> 2.6.3 version of the intel driver. When measuring with my Energy
> Monitor 3000 [1] I did not record any power savings at all. In fact,
> I saw an increase of a couple of deciwatts. (Could be a measuring
> error though).
> Otherwise the system seemed stable and functioned as expected.
> 
> What is the expected power decrease when using this patch?
> 
> Best regards,
> Erik Andrén
> 
> 
> [1]
> http://www.alamaison.com.au/p/361923/voltcraft-plus-energy-monitor-3000.html
I'm not surprised you didn't see any change measuring power usage at the
outlet.  Laptop power supplies are rarely switched mode, and typically
provide their full rating while in use.  They aren't typically designed
with energy efficiency in mind.

If you want to measure the energy efficiency of a laptop, your best bet
is powertop when running from battery.


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