[review] New 'fibocom' plugin

[Ben Chan]

On Thu, Jul 19, 2018 at 12:45 PM Aleksander Morgado
<aleksander at aleksander.es> wrote:
>
> On Thu, Jul 19, 2018 at 9:23 PM, Dan Williams <dcbw at redhat.com> wrote:
> > On Thu, 2018-07-19 at 21:10 +0200, Aleksander Morgado wrote:
> >> > On Chrome OS, we simply use ID_MM_PORT_IGNORE to ignore all AT
> >> > ports
> >> > on the L850-GL module (e.g.
> >> > https://chromium.googlesource.com/chromiumos/overlays/chromiumos-ov
> >> > erlay/+/master/net-misc/modemmanager-next/files/77-mm-fibocom-port-
> >> > types.rules).
> >> >
> >> > The modem is functional with just MBIM and supported via the
> >> > generic
> >> > plugin, which is the approach we took on Chrome OS. IMHO, there is
> >> > little added benefit with a new modem plugin. More importantly, AT
> >> > probing takes quite some time, and I observed it often took 7
> >> > seconds.
> >> > We've been trying hard for some time to move everything to purely
> >> > MBIM
> >> > or QMI :)
> >> >
> >>
> >> I'm going to extend this plugin in the following weeks with more
> >> features that will require the use of the AT port, e.g. GPS location
> >> and such. I agree that probing is a bit slow right now, but that is
> >> just because the DIAG port goes first through a series of AT probing
> >> steps which are not needed. For devices with fixed layouts like this
> >> one, adding udev tags to specify port types isn't bad IMO, and we
> >> should probably do that for the DIAG port (i.e. flag it as "not AT"
> >> for example).
> >
> > Agreed; ideally we can begin to restrict which ports we bother probing
> > for DIAG, since with QMI and MBIM DIAG is much less useful these days.
> >

IIRC, I initially blacklisted two out of the three AT ports, but
initial AT probing still took seconds to complete (and seconds matter
a lot on Chrome OS as we're pretty sensitive to the overall time from
boot to connect), which drove me into blacklisting all AT ports. For
functionality that isn't implemented by standard MBIM command set,
we've pushing for MBIM extensions -- actually, you'll expect a few
related patches from me soon :-)

Regarding your patches, I think they won't interfere with our AT
blacklist on this modem. In the worst case, we can simply skip
installing the fibocom plugin, which should allow us to gracefully
fall back to the generic plugin and use only MBIM.
>
> You may know this better than me; are all DIAG ports from all qualcomm
> modems ever of the same class/subclass/protocol? i.e. Cls=ff(vend.)
> Sub=ff Prot=ff
> In other words, should we bother probing QCDM for ports that are not ff/ff/ff?
>
> --
> Aleksander
> https://aleksander.es