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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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