linux-kernel - Re: [PATCH v2] brcmfmac: add support for CQM RSSI notifications

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Date:   Tue, 19 Jan 2021 09:30:37 +0100
From:   Arend Van Spriel <arend.vanspriel@...adcom.com>
To:     Alvin Šipraga <ALSI@...g-olufsen.dk>,
        Arend van Spriel <aspriel@...il.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-hsien Lin <chi-hsien.lin@...ineon.com>,
        Wright Feng <wright.feng@...ineon.com>,
        Chung-hsien Hsu <chung-hsien.hsu@...ineon.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Andrew Zaborowski <andrew.zaborowski@...el.com>
Cc:     "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "brcm80211-dev-list.pdl@...adcom.com" 
        <brcm80211-dev-list.pdl@...adcom.com>,
        "SHA-cyfmac-dev-list@...ineon.com" <SHA-cyfmac-dev-list@...ineon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] brcmfmac: add support for CQM RSSI notifications

On 1/15/2021 3:57 PM, Alvin Šipraga wrote:
> Hi Arend,
> 
> On 1/15/21 3:10 PM, Arend Van Spriel wrote:
>> + Johannes
>> - netdevs
>>
>> On 1/14/2021 5:36 PM, 'Alvin Šipraga' via BRCM80211-DEV-LIST,PDL wrote:
>>> Add support for CQM RSSI measurement reporting and advertise the
>>> NL80211_EXT_FEATURE_CQM_RSSI_LIST feature. This enables a userspace
>>> supplicant such as iwd to be notified of changes in the RSSI for roaming
>>> and signal monitoring purposes.
>>
>> The more I am looking into this API the less I understand it or at least
>> it raises a couple of questions. Looking into nl80211_set_cqm_rssi() [1]
>> two behaviors are supported: 1) driver is provisioned with a threshold
>> and hysteresis, or 2) driver is provisioned with high and low threshold. >
>> The second behavior is used when the driver advertises
>> NL80211_EXT_FEATURE_CQM_RSSI_LIST *and* user-space provides more than
>> one RSSI threshold. In both cases the same driver callback is being used
>> so I wonder what is expected from the driver. Seems to me the driver
>> would need to be able to distinguish between the two behavioral
>> scenarios. As there is no obvious way I assume the driver should behave
>> the same for both cases, but again it is unclear to me what that
>> expected/required behavior is.
> 
> It will only provision the driver according to behaviour (1) if 0 or 1
> thresholds are being set AND the driver implements
> set_cqm_rssi_config(). But it says in the documentation for the
> set_cqm_rssi_range_config() callback[1] that it supersedes
> set_cqm_rssi_config() (or at least that there is no point in
> implementing _config if range_config is implemented). In that case, and
> if just one threshold is supplied (with a hysteresis), then a suitable
> range is computed by cfg80211_cqm_rssi_update() and provided to
> set_cqm_rssi_range_config(). I guess the implication here is that the
> two behaviours are functionally equivalent. I'm not sure I can argue for
> or against that because I don't really know what the semantics of the
> original API were supposed to be, but it seems reasonable.
> 
> As a starting point - and since the firmware behaviour is very close
> already - I implemented only set_cqm_rssi_range(). I have been testing
> with iwd, which by default sets just a single threshold and hysteresis,
> and the driver was sending notifications as would be expected.

OK. I overlooked that there were two different callbacks involved. So I 
will review the patch with that knowledge. What wifi chip did you test 
this with and more importantly which firmware version?

Regards,
Arend

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