netdev - Re: [PATCH v3 net-next] rndis_host: Flag RNDIS modems as WWAN devices

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Message-ID: <e1c64e01-2076-4d87-8814-8124bfa76d0b@gmail.com>
Date: Sat, 12 Apr 2025 12:08:29 +0700
From: Lars Melin <larsm17@...il.com>
To: Michał Pecio <michal.pecio@...il.com>,
 Lubomir Rintel <lkundrak@...sk>
Cc: linux-usb@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 "David S. Miller" <davem@...emloft.net>, Andrew Lunn <andrew+netdev@...n.ch>
Subject: Re: [PATCH v3 net-next] rndis_host: Flag RNDIS modems as WWAN devices

On 2025-04-12 05:42, Michał Pecio wrote:
> On Tue, 25 Mar 2025 10:58:41 +0100, Lubomir Rintel wrote:
>> Set FLAG_WWAN instead of FLAG_ETHERNET for RNDIS interfaces on Mobile
>> Broadband Modems, as opposed to regular Ethernet adapters.
>>
>> Otherwise NetworkManager gets confused, misjudges the device type,
>> and wouldn't know it should connect a modem to get the device to work.
>> What would be the result depends on ModemManager version -- older
>> ModemManager would end up disconnecting a device after an unsuccessful
>> probe attempt (if it connected without needing to unlock a SIM), while
>> a newer one might spawn a separate PPP connection over a tty interface
>> instead, resulting in a general confusion and no end of chaos.
>>
>> The only way to get this work reliably is to fix the device type
>> and have good enough version ModemManager (or equivalent).
>>
>> Signed-off-by: Lubomir Rintel <lkundrak@...sk>
>> Fixes: 63ba395cd7a5 ("rndis_host: support Novatel Verizon USB730L")
> 
> Hi,
> 
> This patch appears to have caused a regression for some users,
> who opened a bug against the USB subsystem here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=220002
> 
> Regards,
> Michal
> 

Hi,
the problem seems to be that the patch matches devices by their 
class/subclass/proto attributes assuming that all rndis devices matching 
those are rndis usb modems but it also catches rndis tethering with 
phones/tablets.
Better is to match by vid:pid as is done in the cdc_ether driver to flag 
ethernet interfaced modems to become wwan devices.

Lars