Re: ModemManager port grabbing rework

[Dan Williams <dcbw redhat com>]

On Tue, 2012-02-14 at 18:54 +0000, Andrew Bird (Sphere Systems) wrote:
> On Tuesday 14 February 2012, Dan Williams wrote:
> > On Tue, 2012-02-14 at 13:02 +0100, Aleksander Morgado wrote:
> > > On 02/13/2012 09:33 PM, Andrew Bird (Sphere Systems) wrote:
> > > >    Will this redesign allow you to change the udev rule assigned names
> > > > 
> > > > from
> > > > ID_MM_ZTE_PORT_TYPE_MODEM
> > > > to
> > > > ID_MM_PORT_TYPE_MODEM
> > > > etc? I don't think there can be any clash requiring a different
> > > > namespace as the items are fully identified by Vendor / Product IDs
> > > > already.
> > > 
> > > That is fine for me, but not sure if there is any reason for the vendor
> > > namespace in port-type tags. Dan?
> > 
> > I think it's fine too; the question at the time was whether or not
> > different modems had different port needs.  I think for now we have
> > enough information to standardize the udev port type tags between
> > vendors.
> > 
> Excellent news, I guess that's a 0.6 thing only? Are you changing anything 
> else in the udev tagging, say AUX -> AT/QCDM or adding GPS port etc?

Some modems can do GPS on different ports depending on the
configuration, or allow you to detect which port GPS is on, so I'm not
sure GPS tagging is useful in a lot of situations.  Were we to tag GPS
ports, we'd only tag ones where we had no other information except the
static tag, so the tag is a positive-but-not-exclusive indication of GPS
support on that port.  Same thing for AT/QCDM/WMC/CnS/QMI.

We used to use tags exclusively back in the NM 0.7 days before MM, via
HAL .fdi files.  They work some of the time, but they fail spectacularly
when vendors use the same VID/PID for multiple devices and even
chipsets.  One case in point is the Alcatel x200, which is the same
VID/PID as the x060s (1bbb:0000) but use completely different chipsets,
AT command sets, and Windows drivers; the only way to tell them apart is
the firmware version from AT+GMR.  They just *happen* to have the same
modem/aux port layout but that's not something you can depend on in
general.  Other examples include many mobile phones that share the same
VID/PID for different chipsets where you may end up two AT ports or one
AT and one DIAG port.

Third, the way we figure out modem port vs. aux port is to look at the
Windows INF files, and those usually only make a distinction between
"modem" and "aux", not between "modem", "at", "qcdm", etc.  Everything
that's not a modem is lumped into a second INF file for a generic serial
driver, usually with no indication what that aux port is actually used
for.  You have to find that out by sniffing.

In short: I'd expect we could make more extensive use of tags where it's
foolproof and unlikely to change, but it's only a hint and lack of a
port tag still means we have to probe.

Dan