Re: IWD 1.27 with brcmfmac not working for roaming

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

On 10/16/2024 4:04 AM, Denis Kenzior wrote:
> Hi Arend,
> 
>>>
>>> One may question why -67 AP was preferred over -29 one?  We'd need 
>>> logs to answer that question.  It could be the -29 one was simply not 
>>> seen in the scan results at the time of the initial scan / connection.
>>
>> The roaming algorithm is not that intuitive. Roaming and rate 
>> selection are not based on signal strength alone. They may look at PER 
>> (packet error ratio) to decide. -29 dBm might actually be too strong. 
>> I always try to get between -40 and -60 dBm.
> 
> I was mostly thinking of the initial BSS selection which iwd can 
> influence at initial CMD_CONNECT.  iwd sorts APs according to highest 
> expected throughput, but that generally means that if 2 APs are 
> identical, the one with better RSSI wins.  Still, without logs there's 
> no way of knowing why the lower rssi one was picked.

Right. The firmware is probably release version so it will only have 
error prints and that kinda details are not showing. If brcmfmac is 
compiled with CONFIG_BRCMDBG you can enable firmware console logging 
(FWCON) with the 'debug' module parameter [1].

> I'm curious: what are the downsides to using RSSI above -40 dBm?

ear damage ;-) Not entirely joking though. Too strong signal can affect 
reception as well. However, I am not sure at what level those issues 
would show. So my -40 dBm is not backed by technical data. Maybe my 
co-workers doing phy stuff have a better explanation.

>>
>> The nl80211 API actually offer the possibility to affect the BSS 
>> selection. The NL80211_CMD_CONNECT command can have the attribute 
>> NL80211_ATTR_BSS_SELECT for that [2]. When not provided the firmware 
>> will obviously use its default behavior whatever that is. Not sure if 
>> IWD or wpa_supplicant support this, but I am fairly sure brcmfmac 
>> supports it. However I do not know if it also applies to roaming.
> 
> iwd does not.  Doesn't look like wpa_s does either.

Should have done that when I added the nl80211 api change ;-)

Regards,
Arend

[1] 
https://elixir.bootlin.com/linux/v6.11.3/source/drivers/net/wireless/broadcom/brcm80211/brcmfmac/debug.h