linux-kernel - Re: [PATCH v1 2/2] net: usb: cdc

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Date:   Fri, 8 Apr 2022 20:54:34 +0200
From:   Sven Schwermer <sven@...nschwermer.de>
To:     Bjørn Mork <bjorn@...k.no>,
        Lars Melin <larsm17@...il.com>
Cc:     linux-usb@...r.kernel.org,
        Sven Schwermer <sven.schwermer@...ruptive-technologies.com>,
        linux-kernel@...r.kernel.org, oliver@...kum.org
Subject: Re: [PATCH v1 2/2] net: usb: cdc_ether: Add Fibocom MA510 modem

Hi Lars,

On 4/8/22 15:35, Bjørn Mork wrote:
> Lars Melin <larsm17@...il.com> writes:
> 
>> Why do you add this modem to the whitelist?
> 
> I believe the clue is the
> 
>> +	.driver_info = (unsigned long)&wwan_info,
> 
> to set FLAG_WWAN instead of the default FLAG_ETHER | FLAG_POINTTOPOINT

Bjørn is right that this is the reason. The Fibocom MA510 and L610 are 
cellular modems, so they require to be labelled as WWAN devices. As such 
they require to be set up (using AT commands or similar) before the 
connection can be used. Furthermore, WWAN devices get a different 
routing metric assigned by the network manager than regular Ethernet 
devices.

>> The net interface has the correct cdc_ether attributes so the
>> cdc_ether driver should bind automagically without any need for the
>> modem to be in the whitelist.
> 
> Yes, this sort of works against the class driver philosophy.  But we've
> already started down that road, so...
> 
> 
> 
> Bjørn