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

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2012-11-20 at 17:15 +0200, Victor Goldenshtein wrote:
> On 14/11/2012 14:38, Johannes Berg wrote:
> > 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)
> >
> 
> not sure how it can happen if have this check:
> 
> if ((cac_type != NL80211_CHAN_HT20) && (cac_type != NL80211_CHAN_NO_HT))
> 		return -EOPNOTSUPP;
> 
> in both start_radar_detection() & enable_tx() ?

The discussion between Michal and me above was unrelated to DFS :-)

johannes