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

[Lars Melin]

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@xxxxx>
> > 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