[Gta04-owner] wifi power saving

[Andreas Kemnade]

Hi,

there is one thing called ieee80211 power saving mode which puts the
interface into a low power state. So power consumption is reduced when
there is little traffic. Since packets are buffered, the symptons are
higher, irregular ping times. which drop when you use
e.g. ping -i 0.2 host

On GTA02 there was a special command like
wmiconfig -i wlan0 performance / rec
The difference in power consumption is dramatic.

On several other hardware you can simply enable/disable power saving
with iwconfig wlanX power on resp. off.
in iwconfig you have a line
          Power Management:off

The libertas wifi driver supports power management in our
2.6.32-hw-validation kernel. The ping behaviour shows up which I have
demonstrated at the OHSW meeting in Garching.
Now at home (the first thing I did) I connected my pseudo-battery (the
2.6.32 has no hdq support!) to my labor power supply and found the
following values with a bit weird-configured 2.6.32 kernel:
360mA wifi powered off
580mA wifi powered on and iwconfig wlan0 power off
380mA+ spikes wifi powered on and iwconfig wlan0 power on

In e.g. 3.7 there still appears Power Management:on in iwconfig output
but iwconfig power on/off fails.
Power saving needs to be enabled  and disabled by the driver at the
right times.

Reasons:
- One ugly block of code commented out by
  #ifdef TODO
  which needs to be understood to have a good solution 
  That block of code is vital to the power saving stuff so there
  has to be a hack to have any power saving
- driver switched to cfg80211, the interface iwconfig power accesses was
  provided for cfg80211
- some inconsistencies after buffer reorganisation (some code expects
  headers stripped off but gets buffers with headers
- probably other power-saving code which was not adopted when doing
  structural changes in the driver

So for first tries there will be a set of patches where some of them
are hacks and other ones clear bugfixes. 
I will first try to fix 3.7 since there the libertas driver is in good
condition. So I have a better chance to learn how the driver works and
I will not run into other driver problems. 

Regards
Andreas
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