Re: [PATCH v4 2/5] mac80211: use chanctx reservation for AP CSA

[Johannes Berg <johannes@sipsolutions.net>]

On Wed, 2014-05-07 at 11:05 +0200, Michal Kazior wrote:

> > I don't think that works for all drivers - only drivers that actually
> > generate and tx each beacon - but other drivers just update a template.
> > We actually have some pending patches to make that work correctly for
> > the CSA counters, but I'm not really sure what you want to happen in the
> > case that one is switching while the other hasn't yet? Should it stop
> > beaconing? Seems like clients would give up the switch then, no?
> 
> Ah, I completely forgot about the template-based approach.
> 
> But I don't think any beacons should be sent after cs_count=1 on the
> old channel either way. Thus, I would expect template-based drivers to
> stop beaconing after cs_count=1. cs_count=0 is a separate case as it
> means "i can disappear at any time now" and is a special case, not
> what happens after reaching cs_count=1 if I remember correctly.

I'm not really sure how this would work though - drivers that have
firmware generating beacons don't generally seem to be in a position to
just stop that aspect and continue operating otherwise, with active
clients and all that. It seems to me this might be really difficult to
implement.

> Clients should expect next beacon to appear on the new channel after
> seeing beacon with cs_count=1. In that case regular cqm for clients
> should apply.
> 
> Real-world multi-vif CSA will probably be off by up to 1 or 2 beacon
> intervals between vifs which should be disruptive for clients I guess.

"not be disruptive"?

Remind me why we're doing this - didn't you originally have something in
mind that was forcing them all to be synchronized with the switch?

johannes