Re: [PATCH v4 6/6] mac80211: add ap channel switch command/event

[Johannes Berg <johannes@sipsolutions.net>]

On Wed, 2012-11-14 at 13:19 +0100, Michal Kazior wrote:

> > However, then I realised that that still doesn't work -- once initial
> > radar detection is done, it needs to continue while the AP is active. If
> > the channel context was going to be relinquished, or even just the
> > channel changed for a few seconds, it would be unsafe. So as a result,
> > the radar detect operation has to somehow be coupled to the start AP
> > operation and prohibit channel changes and additional channel contexts
> > during the entire operation time.
> 
> Hmm.. cfg80211 doesn't really know about channel contexts.
>
> The problem I see is that cfg80211 may be in a combination with 
> `num_different_channels = 1` and mac80211 can have 2 channel contexts 
> due to channel type incompatibilities.

Yes, this is a concern, we need to fix that anyway though, otherwise it
may assume that some operations are possible when they really aren't
(e.g. starting an HT40+ and HT40- AP on the same channel, which
shouldn't be done anyway, but still)

> We'd need to tell cfg80211 that multi-interface is not possible when DFS 
> is active if we want to at least consider single-channel only DFS.

Not sure about multi-interface, but multi-channel at least.

johannes