Re: [RFC] Fixes for problems with off-channel powersave

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

On Fri, Jan 25, 2013 at 10:34:56PM +0100, Johannes Berg wrote:
> On Wed, 2013-01-16 at 23:35 -0600, Seth Forshee wrote:
> 
> > > I'll address powersave another day, but it also needs major rework.
> > 
> > I can't completely ignore powersave if I want to get brcmsmac working
> > properly. The hardware seems to be actively setting or clearing PM based
> > on its configuration, so I need a way to tell the driver that PM should
> > be set. Making off-channel an explicit powersave state lets me do this,
> > and while it doesn't fix any of the other powersave problems I do think
> > it make the code clearer than the psuedo-state used now for off-channel.
> > 
> > What I've got locally now for this is code to expand the PS config flag
> > to two bits to support three PS states: disabled, enabled, and
> > off-channel. Doing this is working well enough with the two machines
> > I've been testing with (brcmsmac and ath9k). There's an odd side effect
> > on brcmsmac of having PM set in probe request frames during scans, but
> > according to the spec PM should be reserved in those frames anyway.
> 
> I'm a little confused by this. What frames are we sending to the AP
> while we are in powersave? Doesn't the scan code flush etc., and then
> the stop-reason thing would prevent other frames from going out?

That's true, but with Broadcom some driver configuration is needed to
even get it to transmit a nullfunc frame with PM set. Maybe adding a
powersave state is a bit extreme to cover this one corner case. I'm open
to other suggestions ;-)

I'm finishing up testing on my patches to implement the changes you
suggested, and I expect to send them out early next week (probably
Monday). I'll include the powersave changes along with those, so I guess
we can discuss this in more detail then.

> > I pushed the changes to the following if you're interested in taking a
> > look:
> > 
> >   git://kernel.ubuntu.com/sforshee/linux.git mac80211-offchannel
> > 
> > I'm possibly still missing some driver updates that would need to be
> > done, but otherwise the changes should be fairly complete. A major
> > rework of the powersave code is likely to take some time, so is there
> > any chance of getting something like this in place to fix things in the
> > short term?
> 
> Totally, sure. I can hardly lay powersave rewrite on your shoulders :-)
> 
> (Nor would I reject it if you did it though, somebody has to do it
> eventually and given how we don't use this code at all for our device I
> can't really justify doing it myself)

I'll keep it in mind for when I have some extra time. So far I haven't
familarized myself much with the powersave code outside of the pieces
involved with off-channel stuff, and whatever I've had to touch for the
changes I've been making.

Seth