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SubjectRe: bad endpoint address, MOTU FastLane
On Tue, 12 May 2009, Clemens Ladisch wrote:

> David Fries wrote:
> > usb_submit_urb returns -22 EINVAL invalid argument as it is trying to
> > submit an interrupt packet to what is registered as an isoc endpoint.

How does one know which type the endpoint really is? Through prior
experience with the device?

> > The second interface has the same end point addresses as the first.
> > Any suggestions on how to deal with this class of broken hardware?
> >
> > I:* If#= 0 Alt= 0 ...
> > E: Ad=81(I) Atr=03(Int.) MxPS= 4 Ivl=1ms
> > I:* If#= 1 Alt= 0 ...
> > E: Ad=81(I) Atr=01(Isoc) MxPS= 4 Ivl=1ms
>
> AFAICS the USB core memorizes the descriptor belonging to a specific
> endpoint number whenever usb_set_interface() is called. In this case,
> the second interface is initialized later, so the second set of
> descriptors wins.
>
> The driver could call usb_set_interface() again for the first interface
> so that the USB core takes notice of the first set of endpoints again.
> Please try the patch below.
>
> I guess I'll have to write another quirk for this.
>
>
> --- linux/sound/usb/usbmidi.c
> +++ linux/sound/usb/usbmidi.c
> @@ -1779,6 +1779,7 @@
> err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
> break;
> case QUIRK_MIDI_RAW:
> + usb_set_interface(umidi->chip->dev, 0, 0);
> umidi->usb_protocol_ops = &snd_usbmidi_raw_ops;
> err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
> break;

This is only a bandaid. The underlying problem is still there.
Basically, the second interface shouldn't exist at all. The only
proper way to deal with it is to pretend there's only one interface --
which would mean changing the descriptors before the kernel parses
them.

A much easier approach is to throw the device away and replace it with
something that _is_ compliant with the USB specification.

Alan Stern



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