Re: [PATCH] brcmfmac: include missing AP scan feature

[Arend van Spriel <arend.vanspriel@broadcom.com>]

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On 2/28/2022 6:17 PM, James Prestwood wrote:
> Hi Alvin,
> 
> On Sat, 2022-02-26 at 11:27 +0000, Alvin Šipraga wrote:
>> Hi James,
>>
>> James Prestwood <prestwoj@gmail.com> writes:
>>
>>> Hi Alvin,
>>>
>>> On Fri, 2022-02-25 at 22:55 +0000, Alvin Šipraga wrote:
>>>> Hi James,
>>>>
>>>> James Prestwood <prestwoj@gmail.com> writes:
>>>>
>>>>> This driver does not advertise this feature yet scanning with
>>>>> on an
>>>>> AP interface appears to work just fine.
>>>>> ---
>>>>>   drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c |
>>>>> 2 ++
>>>>>   1 file changed, 2 insertions(+)
>>>>>
>>>>> I've submitted this patch mainly to start a discussion about
>>>>> it. I
>>>>> find it hard to believe that ALL brcmfmac devices support AP
>>>>> scanning
>>>>> in which case this feature needs to be limited to those devices
>>>>> only. Trouble is there is no FW feature for AP scanning AFAIK.
>>>>>
>>>>> In any case I think this driver needs to sort out if it
>>>>> supports
>>>>> this
>>>>> feature or not, and advertise as such rather than leaving
>>>>> userspace
>>>>> in the dark.
>>>>
>>>> By the way, what are the typical use-cases for AP scanning?
>>>>
>>>> I know that hostapd does a passive scan on the AP interface on
>>>> the
>>>> assumption that the driver/firmware will gather channel survey
>>>> data,
>>>> but
>>>> that's not a universally applicable assumption. Not all
>>>> implementations
>>>> will do that.
>>>
>>> We have someone wanting it for onboarding/configuring a new
>>> headless
>>> device. Where on boot, if it is unconfigured, it starts an AP and
>>> waits
>>> for a client to configure it.
>>>
>>> A client would connect, have the device scan and present available
>>> networks. The client then selects a network and provides
>>> credentials.
>>> The new device can then switch back to station mode and connect.
>>>
>>> This is a relatively common practice I've seen with IoT devices.
>>
>> Ah OK! Actually we do pretty much the same here at B&O with
>> brcmfmac. But rather than starting the AP on the primary interface
>> (the
>> one default created by the driver), we add a separate AP interface
>> with
>> the equivalent of the following command:
>>
>> # iw dev wlan0 add uap0 type __ap
>>
>> Here wlan0 is the primary interface, and uap0 is what I call my AP.
>>
>> In that case you can start the AP on uap0, but still do scanning on
>> wlan0 (which remains in station mode). Don't quote me on it, but I
>> think
>> this is the canonical approach with this driver. Is it something you
>> have considered?
> 
> Thanks, this does seem to work on brcmfmac. I had tried this on other
> hardware without any luck. I mentioned this to the user but since the
> AP scanning feature has been implemented they may want to still use
> that, but who knows. I think finding out if brcmfmac is intended to
> scan on the AP interface would still be good to know.

There is no easy answer to that. It really depends on the 
device/firmware. To be honest I don't know if the older chips can 
support it. Need to check that.

What device are you specifically looking at?

Regards,
Arend

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