Re: [PATCH 1/4] mac80211: Convert PS configuration from a binary flag to a set of modes

[Seth Forshee <seth.forshee@canonical.com>]

On Wed, Feb 13, 2013 at 07:54:19PM +0100, Arend van Spriel wrote:
> On 02/13/2013 06:04 PM, Seth Forshee wrote:
> >> Is all this really worth it? It seems a quick fix for brcmsmac might be
> >> > to always set the powersave bit when IEEE80211_CONF_OFFCHANNEL is
> >> > enabled in the config, and then go implement a real solution like I
> >> > described earlier with powersave being separated out of the core
> >> > mac80211 routines, and actually made possible for multiple interfaces?
> > Using IEEE80211_CONF_OFFCHANNEL won't work. When the nullfunc to enable
> > PS is sent the flag won't be set, as we're still on the operating
> > channel. When we're actually off-channel the value of PM doesn't matter
> > for the types of frames which are being sent. The only quick fix I've
> > found is to watch out for frames with PM set and set the powersave bit
> > while they're being transmitted.
> 
> I actually don't see that one fly. The frames are posted on a DMA fifo
> towards the hardware so in the driver we have no clue when that frame is
> being processes/transmitted hence no way of knowing when to write the
> register(s).

There's a couple of ways of doing it. I had a working patch at one point
but can't seem to find it now, so I'm not sure which way I used. You're
right though that we can't tell when the hardware is actually processing
or transmitting the frame, so in either case MCTL_HPS has to be set
before you put the frame in the tx fifo.

The first option is that for any frame with PM set, set MCTL_HPS when
mac80211 hands off the frame and clear it once it has finished
transmitting.

The second option is to look specifically for nullfunc frames and set or
clear MCTL_HPS based on the value of PM.

Either of these should work fine with the current mac80211 code, but
overall the second one is probably a little safer.

Seth