Re: [PATCH] mac80211: implement STA CSA for drivers using channel contexts

[Johannes Berg <johannes@sipsolutions.net>]

On Fri, 2013-08-16 at 23:09 +0300, Arik Nemtsov wrote:

> > Well, it can't. If you look carefully then the old chan_switch op
> > behaviour is to let the driver switch, not switch in software
> > afterwards.
> 
> The right thing for chan_switch drivers would be not to call hw_config()..

chan_switch? or chanctx?

> > Yeah but it's (currently) meant for interfaces controlling the CSA (i.e.
> > AP only right now) ... so I really think we need to make this
> > controllable, I think that when we want to implement it for Intel MVM
> > firmware then we'll let the firmware control the switch timing, etc.
> > None of this can even be done today or with your patch.
> 
> The TI driver implements the chan_switch op and uses channel contexts.

Huh, ok, that was a combination I didn't think was going to exist, since
the chanswitch API doesn't really tell you what channel context etc.
OTOH, it does give you the vif so you have the chanctx implicitly.

> If I catch your drift you would rather these kind of drivers (which
> include MVM) use a new API exposed by mac80211 to complete the channel
> switch. This API would basically be ieee80211_vif_change_channel(). Do
> we still need to touch the cfg80211 chandef definition in ifmgd?

That's what I was thinking, yes.

> The above is maybe cleaner, but it's functionally equivalent to the
> solution today - the low level driver decides when the channel switch
> is completed, and ieee80211_chswitch_work() is called, which does the
> right thing for all cases.

Right ... I guess that works.

> Note that with the above, the channel_contexts + software chan-switch
> drivers will still need the kind of code that I wrote. So it would
> just lead to replicated code. Or maybe you meant something else?

We have too many possibilities I guess ... I think for MVM I want the
disconnect, not the channel context change in software. You're taking
that possibility away, hence my suggestion of a new hardware flag for it
or so.

> Also, where would you put csa_active = true (if at all) for a STA
> interface? Unlike AP, the trigger here is mac80211 code. So putting it
> there seemed appropriate.

Yeah, I was really just trying to say that current chanctx drivers need
not really expect a chanctx to change channel unless they implement CSA,
but that currently means AP-CSA - basically what I just said above with
taking away the possibility of doing the deauth instead.

johannes