Re: [PATCH v4 5/6] nl80211/cfg80211: add ap channel switch command

[Victor Goldenshtein <victorg@ti.com>]

On 05/11/2012 17:29, Johannes Berg wrote:
> On Thu, 2012-11-01 at 09:54 +0200, Victor Goldenshtein wrote:
>
>>> This however introduces a new problem. Let's suppose we have 2 APs on
>>> channel 1. The device doesn't support multi-channel. We won't be able to
>>> switch channel on these APs at all.
>>>
>>> We might want to change the channel switch to resolve around the channel
>>> itself (not the interface) - so we'd be saying "move all interfaces with
>>> channel X to channel Y" instead of "move interface X to channel Y".
>>>
>>> Or we could let the driver decide what it'll do - e.g. silently switch
>>> more than one interface to a different channel (which makes sense with
>>> AP/DFS I guess) and just notify cfg/userspace about it. That would
>>> require us to provide a way to switch interfaces (atomically possibly)
>>> between channels while keeping in sync with interface combinations though.
>>>
>>
>> If the driver/device supports MR only on a SC - means it doesn't
>
> What's MR? SC = single channel?
>

MR - Multi-Role, SC - Single Channel.

>> supports channel switch in MR, so basically the radar detection event
>> triggers AP channel switch which fails (with this new check) and the AP
>> shut down.
>
> But I was speaking of two interfaces on a single channel.
>

the radar detection is per channel and for this case we have the 
"if·(chan->cac_started)" check, see 6/6.

>> Of course there are possible driver specific workarounds (as you
>> mentioned above) but these are not part of this series.
>
> yeah but you should probably allow for some strategy of handling this?
>

If we talking about the case of running two APs on the same channel on a 
single channel platform then the strategy should be (at least at first 
stage) to shut down both APs after radar detection event.

Later we can discuss about the idea of "switching interfaces" (switch 
both this APs to a new channel).


-- 
Thanks,
Victor.