Re: [RFC 3/6] wifi: mac80211: notify driver about per-radio monitor enabled state

[Johannes Berg <johannes@sipsolutions.net>]

On Fri, 2024-08-23 at 13:26 +0200, Felix Fietkau wrote:
> 
> > On 23. Aug 2024, at 12:16, Johannes Berg <johannes@sipsolutions.net> wrote:
> > 
> > On Mon, 2024-08-05 at 21:23 +0200, Felix Fietkau wrote:
> > > This allows monitoring on one or more radios while minimizing performance
> > > impact on the others.
> > 
> > But why are you doing it this way? You could already solve this entirely
> > with the driver by setting WANT_MONITOR_VIF and dealing with that, I'd
> > think? At least after this series.
> > 
> > I generally don't like hw->conf, it just hasn't really matched reality
> > for years with all kinds of new concurrency capabilities. At the very
> > least you'd have to write more text here to convince me that we want to
> > add something to it ... :)
> 
> I really don’t see how WANT_MONITOR_VIF helps. It seems completely unrelated to me, since it only creates a single driver visible vif, if there are no non-monitor vifs on the phy.

Well, it's true that it only creates one towards the driver, but that
one vif can also only be bound to a single channel context, and
therefore a single radio.

If we actually want(ed) to support monitoring on different radios
simultaneously we'd have to change mac80211 quite a bit, and probably
introduce multiple virtual monitor interfaces. Internally, we _always_
have it now, to be able to bind a channel context, so we'd actually need
multiple - one for each possible parallel channel.

So that's why I think having WANT_MONITOR_VIF helps - you can assume
today that only one chanctx can be used for monitoring, and once you
have the monitor vif in hand, you know which one it is. Therefore you
know which radio it is, and can adjust your offloads/etc. accordingly.

> I want to be able to control, which radios I want to capture on, regardless of which vifs are already active on the same phy.

Sure.

> A global monitor enable/disable status means that I can’t prevent monitor-incompatible offloads from being disabled on radios that I’m not monitoring on.
> 

Yeah I'd just say don't use that state, but the presence of the monitor
vif, and you can figure out which radio it's present on.

johannes