Blacklisting a broken AT port

[Dan Williams]

On Thu, 2014-01-30 at 00:48 -0800, Ben Chan wrote:
> Dan,
> 
> Thanks for your suggestion. That solves one of the issues I encountered.
> I've submitted a patch to add additional hints for a ZTE MF190 dongle.  I
> may need to implement a similar solution for other modems.

Yeah, it's somewhat hard keeping up with all the devices vendors put out
here.  The best way to do it, if you don't have documentation or
guidance from the OEM, is to grab the Windows INF files and find out
that way.

This doesn't work as well for Sierra and other vendors like Huawei
though, because they can change port layout based on AT commands or
usb_modeswitch configuration or stuff like that.

Dan

> Ben
> 
> 
> On Wed, Jan 29, 2014 at 8:20 AM, Dan Williams <dcbw at redhat.com> wrote:
> 
> > On Wed, 2014-01-29 at 00:04 -0800, Ben Chan wrote:
> > > Hi Aleksander,
> > >
> > > I notice that some dongles have broken AT ports, e.g. ttyUSB1 appears to
> > be
> > > AT-capable but fails to handle most AT commands, while ttyUSB3 is
> > > completely functional. ModemManager may pick ttyUSB1 as primary and
> > ttyUSB3
> > > as secondary.
> > >
> > > What's the recommended way to blacklist ttyUSB1 in such case?  I guess I
> > > could add a udev rule to avoid setting MM_CANDIDATE=1 on ttyUSB1.
> >
> > We try to avoid per-port blacklisting because it's got a lot of
> > possibility for abuse for reasons kinda like this.  Not that your case
> > is a problem, but that in general per-port blacklisting is a
> > sledgehammer that often causes collateral damage.  I'd rather use
> > affirmative hints to mark some ports as primary and others as secondary
> > in these cases, instead of blacklisting.
> >
> > But this is actually SOP for ZTE and other devices.  Usually we have to
> > scrape the windows INF files to find the modem and control ports, which
> > then get encoded into the udev rules.  So if you have a device where the
> > wrong port is being picked automatically, then we should certainly add
> > some port hints for it.  See 77-mm-zte-port-types.rules for example.
> >
> > Dan
> >
> >
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