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Subject: Re: [PATCH 06/12] iwlwifi: mvm: Add support for 6GHz passive scan
To:     "Peer, Ilan" <ilan.peer@intel.com>, Luca Coelho <luca@coelho.fi>,
        "kvalo@codeaurora.org" <kvalo@codeaurora.org>
Cc:     "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
References: <20210331091452.543321-1-luca@coelho.fi>
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From:   Ben Greear <greearb@candelatech.com>
Organization: Candela Technologies
Message-ID: <eb60c152-81ac-2977-87fc-f724d4d6ccf0@candelatech.com>
Date:   Sun, 11 Apr 2021 04:16:58 -0700
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On 4/11/21 3:14 AM, Peer, Ilan wrote:
> Hi Ben,
> 
>> -----Original Message-----
>> From: Ben Greear <greearb@candelatech.com>
>> Sent: Wednesday, March 31, 2021 15:04
>> To: Luca Coelho <luca@coelho.fi>; kvalo@codeaurora.org
>> Cc: linux-wireless@vger.kernel.org
>> Subject: Re: [PATCH 06/12] iwlwifi: mvm: Add support for 6GHz passive scan
>>
>> On 3/31/21 2:14 AM, Luca Coelho wrote:
>>> From: Ilan Peer <ilan.peer@intel.com>
>>>
>>> When doing scan while 6GHz channels are not enabled, the 6GHz band is
>>> not scanned. Thus, if there are no APs on the 2GHz and 5GHz bands
>>> (that will allow discovery of geographic location etc. that would
>>> allow enabling the 6GHz channels) but there are non collocated APs on
>>> 6GHz PSC channels these would never be discovered.
>>>
>>> To overcome this, FW added support for performing passive UHB scan in
>>> case no APs were discovered during scan on the 2GHz and 5GHz channels.
>>>
>>> Add support for enabling such scan when the following conditions are
>>> met:
>>>
>>> - 6GHz channels are supported but not enabled by regulatory.
>>> - Station interface is not associated or less than a defined time
>>>     interval passed from the last resume or HW reset flows.
>>> - At least 4 channels are included in the scan request
>>> - The scan request includes the widlcard SSID.
>>> - At least 50 minutes passed from the last 6GHz passive scan.
>>
>> Why are you trying so hard to not do passive scans?  This seems like it is set
>> up for all sorts of frustration.
>>
> 
> This logic enables a special 'passive' scan which is not directly intended for discovery of APs for connection etc. but
> for discovery of APs with country information in the beacons/probe responses, so the fw could use this information
> as an input that might allow it to enable 6GHz channels (which are supported but are disabled). This special scan
> is intended for cases that the device does not have any other regulatory information that allows it to enable the 6GHz channels.
> Once these channels are enabled, we use passive scan as needed.
> 
> We generally try to avoid passive scan on all the 6GHz channels as this is a long flow that takes at least 6 seconds (as there are
> such 64 channels) and with the discovery mechanisms defined for the 6GHz is not really needed.

If the station comes up and does a 6E passive scan and does not find any AP, perhaps because 6Ghz AP was turned on 1 minute after the station
tried to initially scan, this means that it will take 50 minutes before it can have a chance to scan
the AP and connect to the Internet?  If station cannot connect after a relatively short time,
then I think it should scan as widely as it can in order find some possible way to connect.

And why care about 'at least 4 channels'.  If we know the AP channel, and can scan exactly there, then your
concern about taking a long time is resolved.

How else can we tell the radio that 6E is allowed?  I previously tried all sorts of things
to enable 6E channels so that I could more easily set the radio to sniff one of those channels
in monitor mode, and I had no luck.

If all of the 6E channels are marked as passive, what harm is it to enable the channels
in the regdom from the beginning?

Thanks,
Ben

> 
> Hope this clarifies things.
> 
> Regards,
> 
> Ilan.
> 


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com