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

[Victor Goldenshtein <victorg@ti.com>]

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() ?

>> 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.
>

Agree, maybe you have an idea how we should do this ?


-- 
Thanks,
Victor.