Fibocom L850-GL hangs upon connect.

[Dan Williams]

On Wed, 2018-08-15 at 20:50 +0200, Vincent Bernat wrote:
>  ❦ 13 août 2018 21:02 +0200, Aleksander Morgado <aleksander at aleksande
> r.es>:
> 
> > > If this modem is going to end up stuck with pure PPP and
> > > therefore maxing
> > > out at 25Mbps, then I'm not too concerned anyways since its use
> > > is rather
> > > limited. I just wish I could figure out how to switch this thing
> > > to MBIM
> > > (Tried everything listed in the AT Command reference guide,
> > > including
> > > factory resets and defaults.).
> > > 
> > 
> > Talked to Fibocom engineers and unfortunately that firmware version
> > you're using cannot do MBIM :/
> 
> On the latest Lenovo X1/T580/T480, this modem is plugged on a
> PCIe-enabled M2 port and boots as a PCI device. It seems Linux isn't
> able to handle that. People tried to tape the PCIe pins to make it
> boot
> as USB, but it's then blacklisted in the BIOS. Maybe you have some
> hints
> on how to make this modem switch to USB after booting?
> 
> I don't own one yet, so I cannot really help with the specifics.
> 
> Relevant thread:
>  https://forums.lenovo.com/t5/Linux-Discussion/Linux-support-for-WWAN
> -LTE-L850-GL-on-T580-T480/m-p/4067969

Yeah, looking at the Hardware User Manual it does indeed look like the
modem provides a PCIe interface rather than a USB one.  cdc-mbim does
not support PCIe, since cdc-mbim is a USB specification.  It would be
very interesting to snoop the PCI traffic for this device.

But in the end, somebody needs to write a driver to talk to the modem
via PCIe rather than USB.  The only other device I have ever
encountered that uses PCI directly is the Option "nozomi" UMTS devices
from 10 years ago before USB became popular for modems.  See the
kernel's source in drivers/tty/nozomi.c for that, but it would
obviously be different for the Fibocom device.

Dan