From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg KH <greg@kroah.com>
Date: Thu, 20 Jan 2011 17:52:11 +0000
Subject: Re: Proper way to get USB class codes
Message-Id: <20110120175211.GB30124@kroah.com>
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On Sat, Jan 15, 2011 at 07:26:28PM +0100, Jos=E9 F=E9lix Onta=F1=F3n 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.
>=20
> First of all, using udevadm i've realized some usb devices left the
> class/subclass/protocol attributes with 00:
>=20
>     ATTR{bDeviceClass}=3D"00"
>     ATTR{bDeviceSubClass}=3D"00"
>     ATTR{bDeviceProtocol}=3D"00"
>=20
> 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