Re: USB networking (cdce) with Linux host (g_ether)

[Christof Meerwald <cmeerw%cmeerw.org@localhost>]

On Sat, Apr 04, 2015 at 04:15:40PM +0900, Ryo ONODERA wrote:
> From: Christof Meerwald <cmeerw%cmeerw.org@localhost>, Date: Sat, 4 Apr 2015 08:42:23 +0200
> > On Sat, Apr 04, 2015 at 08:50:01AM +0900, Ryo ONODERA wrote:
> >> Please remove cdce(4) and umodem(4) entries from your kernel configuration
> >> file (your device should be recognized as ugen(4)) and run
> >> $ gcc -o probe_usb probe_usb.c
> >> # ./probe_usb /dev/ugen0.00
> > 
> > # ./probe_usb /dev/ugen0.00
> > length: 9
> > descriptor type: 2
> > total length: 2147470578
> > num interface: 2
> > config value: 2
> > configuration: 0
> > Attributes: (0xc0) Self powered 
> > max power: 500 mA
> > 
> > Interface 0:
> >   Length: 9
> >   Descriptor Type: 4
> >   Interface No: 0
> >   Alt Setting: 0
> >   Num Endpoints: 1
> >   Interface Class: 2
> >   Interface SubClass: 2
> Your cdce(4) has Interface Class Subclass = 2.
> According to table 16 of
> http://cscott.net/usb_dev/data/devclass/usbcdc11.pdf
> Universal Serial Bus Class Definitions for Communication Devices Version 1.1,
> 02h is assigned to Abstract Control Model.
> As far as I understand correctly, Abstract Control Model is used for
> RS-232C emulation devices, for example USB modem.

I don't think that's actually causing the problem - if you look in
umodem.c it checks for

  if (uaa->class != UICLASS_CDC ||
      uaa->subclass != UISUBCLASS_ABSTRACT_CONTROL_MODEL ||
      !(uaa->proto == UIPROTO_CDC_NOCLASS || uaa->proto == UIPROTO_CDC_AT))
          return (UMATCH_NONE);

and the proto is 255 in my case and that causes it to return
UMATCH_NONE

> > Interface 1:
> >   Length: 9
> >   Descriptor Type: 4
> >   Interface No: 1
> >   Alt Setting: 0
> >   Num Endpoints: 2
> >   Interface Class: 10
> >   Interface SubClass: 0
> >   Interface Protocol: 0

I think that's actually the one that causes the problem in r1.66 of
umodem.c

  id = usbd_get_interface_descriptor(uaa->iface);
  if (uaa->subclass != UISUBCLASS_ABSTRACT_CONTROL_MODEL &&
      (id->bInterfaceClass == UICLASS_CDC_DATA &&
       id->bInterfaceSubClass == UISUBCLASS_DATA))
          return (UMATCH_IFACECLASS_IFACESUBCLASS);

Now I have to say that I don't have much understanding of the NetBSD
code base or USB, but this is my understanding:

Looking at usbd_attachinterfaces uiaa (which I think is then uaa in
umodem.c) gets populated as:

  uiaa.iface = ifaces[i];
  uiaa.class = ifaces[i]->idesc->bInterfaceClass;
  uiaa.subclass = ifaces[i]->idesc->bInterfaceSubClass;

usbd_get_interface_descriptor(uaa->iface) just returns uaa->iface->idesc

I would therefore always expect id->bInterfaceClass == uaa->class and
id->bInterfaceSubClass == uaa->subclass and the above 'if' could then
be rewritten as:

  if (uaa->class == UICLASS_CDC_DATA &&
       uaa->subclass == UISUBCLASS_DATA)
          return (UMATCH_IFACECLASS_IFACESUBCLASS);

which clearly looks wrong to me.


I could of course be wrong here, but I don't see how uaa->subclass can
be different from id->bInterfaceSubClass in that code.


Christof

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