Proper way to get USB class codes

Proper way to get USB class codes

[José Félix Ontañón]

Hello everybody,
I've got some doubts and problems getting USB class codes via udev and
i'll be very grateful if someone could clarify.

First of all, using udevadm i've realized some usb devices left the
class/subclass/protocol attributes with 00:

    ATTR{bDeviceClass}="00"
    ATTR{bDeviceSubClass}="00"
    ATTR{bDeviceProtocol}="00"

Is that an issue on the usb device itself or an issue on udev reading
usb device/interface descriptor?

Second, i've some doubts about when should I use the
ID_USB_INTERFACES, TYPE or INTERFACE property: in which cases should I
use one or another? Why the TYPE property sometimes appear as 0/0/0
even when the ID_USB_INTERFACES and INTERFACE properties are filled?

Thanks for sharing your thoughs.

-- 
http://fontanon.org

Re: Proper way to get USB class codes

[José Félix Ontañón]

El día 15 de enero de 2011 19:26, José Félix Ontañón
<felixonta@gmail.com> escribió:
> Hello everybody,
> I've got some doubts and problems getting USB class codes via udev and
> i'll be very grateful if someone could clarify.
>
> First of all, using udevadm i've realized some usb devices left the
> class/subclass/protocol attributes with 00:
>
>    ATTR{bDeviceClass}="00"
>    ATTR{bDeviceSubClass}="00"
>    ATTR{bDeviceProtocol}="00"
>
> Is that an issue on the usb device itself or an issue on udev reading
> usb device/interface descriptor?
>
> Second, i've some doubts about when should I use the
> ID_USB_INTERFACES, TYPE or INTERFACE property: in which cases should I
> use one or another? Why the TYPE property sometimes appear as 0/0/0
> even when the ID_USB_INTERFACES and INTERFACE properties are filled?
>
> Thanks for sharing your thoughs.

Hello everyone,

I've been doing some tests and the fact is I think this could be an
udev bug: HAL reports class/subclass/protocol for all USB devices with
no failures at all. Here the same example as above but using HAL:

  usb.interface.class = 11  (0xb)  (int)
  usb.interface.subclass = 0  (0x0)  (int)
  usb.interface.protocol = 0  (0x0)  (int)

After had been looking through bugzilla.kernel.org I realized there
weren't any bug reported about it. Does anyone think, like me, this
could be a bug? Would somebody tell me if i can perform some more
tests before reporting the bug myself?

Thanks in advance.

-- 
http://fontanon.org

Re: Proper way to get USB class codes

[Greg KH]

On Sat, Jan 15, 2011 at 07:26:28PM +0100, José Félix Ontañón wrote:
> Hello everybody,
> I've got some doubts and problems getting USB class codes via udev and
> i'll be very grateful if someone could clarify.
> 
> First of all, using udevadm i've realized some usb devices left the
> class/subclass/protocol attributes with 00:
> 
>     ATTR{bDeviceClass}="00"
>     ATTR{bDeviceSubClass}="00"
>     ATTR{bDeviceProtocol}="00"
> 
> Is that an issue on the usb device itself or an issue on udev reading
> usb device/interface descriptor?

No, that's normal, why wouldn't it be?  Those attributes are properly
defined for these devices in the interface values for those fields, not
the main device values.

> Second, i've some doubts about when should I use the
> ID_USB_INTERFACES, TYPE or INTERFACE property: in which cases should I
> use one or another? Why the TYPE property sometimes appear as 0/0/0
> even when the ID_USB_INTERFACES and INTERFACE properties are filled?

That's normal, and to be expected.  Please read the usb.org specs for
details if you really are curious.

thanks,

greg k-h