[RFC] No multiplexing by default in MM 1.18

[Reinhard Speyerer]

On Wed, Aug 04, 2021 at 09:37:04AM +0200, Aleksander Morgado wrote:
> Hey Reinhard,
> 
> > > > I've been testing with all my modems for the next 1.18 release, and
> > > > for the QMI and MBIM ones I've done tests with and without
> > > > multiplexing support (i.e. connecting normally as we did until now,
> > > > and also connecting with multiplexing enabled).
> > > >
> > > > All the QMI modems I have tested with have worked fine. If QMAP wasn't
> > > > supported by the modem and we were requesting multiplexing, it would
> > > > automatically just fallback to no multiplexing (802.3 or plain
> > > > raw-ip), and that was it.
> > > >
> > > > Most of the MBIM modems I have tested with have worked fine as well,
> > > > with the exception of the Netgear AC340U, which would reply with
> > > > "InvalidParameters" if we were attempting to connect any session with
> > > > id != 0. All the other modems have been able to correctly setup
> > > > multiplexing when requested without issues.
> > > >
> > > > Even if the tests have been quite satisfactory overall (I've tested
> > > > >60 different modems in the past month), I think that for 1.18 we
> > > > should not enable multiplexing by default (except for IPA), and still
> > > > leave it as a requirement from the user at connect time. So, if the
> > > > user wants to setup a connection with multiplexing enabled, it should
> > > > pass either "multiplex=requested" or "multiplex=required" in the
> > > > connection settings explicitly
> > > >
> > > >
> > > I think it makes sense.
> > >
> >
> > I too think it makes sense to not enable multiplexing by default at
> > this point in time.
> >
> > Since commit 44f82312fe91 ("qmi_wwan: add network device usage statistics
> > for qmimux devices") of my "qmi_wwan: fix QMAP handling" series
> > https://lore.kernel.org/netdev/cover.1560287477.git.rspmn@arcor.de
> > was not backported to 4.14.x and 4.19.x longterm kernels by Sasha Levin's
> > "AUTOSEL" patches this would introduce a regression for users of those
> > kernel versions with MM 1.18 otherwise.
> >
> 
> Oh, thanks for pointing that out. I always try to test with the latest
> available kernel in Arch, and not so much with older kernels, but it's
> definitely something to take into account. That patch was included in
> Linux 5.2 for what I can tell, right?

Hi Aleksander,

yes, that's Linux 5.2 and now also Linux 4.19.203 and Linux 4.14.244.

> Note that if rmnet is available, the ModemManager logic currently
> defaults to using rmnet instead of qmi_wwan add_mux/del_mux, which has
> some limitations in some older kernel versions as well.

According to a quick check at git.kernel.org Daniele's
"net: usb: qmi_wwan: allow qmimux add/del with master up" patch was
applied to all relevant longterm kernels (4.14, 4.19, 5.4 and 5.10).

Regards,
Reinhard