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

[Michal Kazior <michal.kazior@tieto.com>]

On 14/11/12 12:23, Johannes Berg wrote:
> On Tue, 2012-11-13 at 17:04 +0200, Victor Goldenshtein wrote:
>
>>> No ... channel contexts are in the kernel now, so you do have to think
>>> about it now.
>>
>> Well thinking is one thing implementing is another ;)
>
> Well ... :)
>
>> This whole DFS implementation initially intended for a single channel
>> mac. I don't might to deal with the channel context stuff but not sure
>> how much available time I"ll have for it, so it might take awhile.
>> I know there are people waiting for this, so I'm thinking would you
>> consider to go first with this single channel DFS support and later to
>> extend it to work with channel context stuff ?
>
> Fair enough, but like I've been telling you, the current code doesn't
> even match the current APIs.
>
> Initially, I thought that for radar detection, you need to reserve the
> channel context (in mac80211), make sure it's the only channel context
> and prohibit other channel contexts from being added, until radar
> detection is done.
>
> 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.

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.


-- Pozdrawiam / Best regards, Michal Kazior.