power management on the 8686 chipset

[Jeff Sutherland]

On Tuesday 01 September 2009, Andrey Yurovsky wrote:
> On Mon, Aug 31, 2009 at 6:54 AM, Jeff Sutherland<jeffs at fomsystems.com> 
wrote:
> > I've backported the latest driver code from John's wireless-testing git
> > repo to my 2.6.30 kernel, and whilst normal operation is fine, I still
> > can't get the part into IEEE power saving mode using iwconfig or iwlist.
> >  What is the command to put the libertas 8686 chip (sdio interface) into
> > power saving mode?  Platform is PXA270 using the OpenEmbedded distro.
>
> # iwconfig ethN power on
>
> How are you verifying that IEEE PS mode is activated?
>
>   -Andrey

I don't know how many times in the past I tried that command and never noticed 
anything taking effect.  Ideed, 'iwconfig wlan0' would always report power 
management as being off even after running that command.  This morning I try 
it again and for the first time I'm seeing current reduction plus 'iwconfig 
wlan0' reports power management as on.  Must be some magic in the air today 
or something, as I thought I was running the latest libertas code from 
wireless-testing.  Anyway, seems to work now :-)

With the system at idle, no other power management in the kernel enabled, 
associated with an A/P, without power management enabled battery drain is a 
consistent 365mA.  Once power management is enabled, input current drops to 
about 191mA most of the time, which briefly jumps back up to 365mA every two 
seconds as the link sits idle with no traffic.  Current jumps around a little 
bit depending on network traffic.  A big rsync transfer shows little increase 
in average power (probably because it's waiting for the flash file system, 
the transfer rate isn't all that fast).  But bottom line is the power savings 
are considerable with little apparent effect on operations.

For all list members:
Another thing I'm concerned with is what's happening at the A/P end, as it has 
to keep track of which clients are in IEEE power saving mode and do some 
buffering of traffic for them.  I'm using a Linksys WRT54GS with the dd-wrt 
firmware, and for one client it works fine.  But I suspect that a little box 
like this could possibly get overwhelmed rather quickly if it had a lot of 
wireless clients in IEEE mode and a moderate amount of network traffic.  
Opinions? Experiences?

Regards,
-Jeff
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