On Wed, 8 Mar 2006, David Brownell wrote: > > In this case it wouldn't make any difference, since all the altsettings > > for a particular interface are supposed to have the same bInterfaceClass, > > bInterfaceSubClass, and bInterfaceProtocol. Although I don't think the > > USB spec actually says this anywhere.. > > I'd have stopped at "wouldn't make any difference"; the kernel must make > some initial choice, but userspace is free to revise it. Agreed it would > be odd if altsettings had different class/subclass/protocol, but I don't > see any good reason to make that illegal.
Agreed. And like I said before, this is only a heuristic. > > The bMaxPower value could be different for different altsettings. > > Erm, no; that's a per-configuration thing, not a per-altsetting thing. > It's checking the config descriptor, not the interface descriptor, > for that particular concern. Whoops, yes. I misread the code. All the more reason not to worry about any but the first altsetting. > > > > b) How do we know that there's actually anything _there_? The length of > > > > that variable-sized array doesn't seem to have been stored anywhere > > > > obvious by usb_parse_configuration() and choose_configuration() > > > > doesn't > > > > check. What happens if the length was zero? > > > > > > I don't think it is allowed to be, as all USB devices have to have at > > > least 1 interface. > > I think that's not true, and it would be worth verifying that it's not > a no-interfaces device even if the USB spec required it. It's trivial > to create device firmware that advertises no-interfaces, and those should > never be able to make Linux hiccup (much less oops). Ha! "should never be able" indeed. It turns out the code doesn't like it if a configuration has no interfaces. How embarassing... Andrew, if you tell us what's in your /proc/bus/usb/devices we'll see whether that was the real problem. In any case, a patch follows. Alan Stern ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel