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From:   Janusz Dziedzic <janusz.dziedzic@gmail.com>
Date:   Sun, 29 Aug 2021 19:56:20 +0200
Message-ID: <CAFED-j=FGHJv+NQZMfN+xEfNB9L51EeU+-1BKjcZ0kX-K925nw@mail.gmail.com>
Subject: Re: CAC question: DFS -> non-dfs -> DFS
To:     Ben Greear <greearb@candelatech.com>
Cc:     "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
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pt., 20 sie 2021 o 18:45 Ben Greear <greearb@candelatech.com> napisa=C5=82(=
a):
>
> Hello,
>
> While poking at the MTK driver and trying to fix some CAC bugs in it,
> I noticed the following:
>
> Select ch 100, which enables DFS CAC logic.  Wait for that to finish.
> Then select CH 36 (disable DFS)
> Then select ch 100 again, and the chandef->chan->dfs_state is set back to=
 0
> which I think means we must do CAC again.
>
> I was expecting in this case that the DFS state would be set to NL80211_D=
FS_AVAILABLE
> instead, since CAC just passed a few minutes prior?
>

This depends on DFS region (country).
EU allow preCAC - once you pass CAC then you can switch to other
channel and - the old one will be DFS_AVAILABLE - no need to do CAC
again.
All other regions don't allow preCAC - so each channel switch will
clear DFS_AVAILABLE and require CAC again.

BR
Janusz