sound: usb-audio: make the MotU Fastlane work again

Kernel 2.6.18 broke the MotU Fastlane, which uses duplicate endpoint
numbers in a manner that is not only illegal but also confuses the
kernel's endpoint descriptor caching mechanism.  To work around this, we
have to add a separate usb_set_interface() call to guide the USB core to
the correct descriptors.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Reported-and-tested-by: David Fries <david@fries.net>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 11 insertions, 1 deletions

diff --git a/sound/usb/usbmidi.c b/sound/usb/usbmidi.c
index 26bad373fe65..2fb35cc22a30 100644
--- a/sound/usb/usbmidi.c
+++ b/sound/usb/usbmidi.c
@@ -1778,8 +1778,18 @@ int snd_usb_create_midi_interface(struct snd_usb_audio* chip,
                 umidi->usb_protocol_ops = &snd_usbmidi_novation_ops;
                 err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
                 break;
-        case QUIRK_MIDI_RAW:
+        case QUIRK_MIDI_FASTLANE:
                 umidi->usb_protocol_ops = &snd_usbmidi_raw_ops;
+                /*
+                 * Interface 1 contains isochronous endpoints, but with the same
+                 * numbers as in interface 0.  Since it is interface 1 that the
+                 * USB core has most recently seen, these descriptors are now
+                 * associated with the endpoint numbers.  This will foul up our
+                 * attempts to submit bulk/interrupt URBs to the endpoints in
+                 * interface 0, so we have to make sure that the USB core looks
+                 * again at interface 0 by calling usb_set_interface() on it.
+                 */
+                usb_set_interface(umidi->chip->dev, 0, 0);
                 err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
                 break;
         case QUIRK_MIDI_EMAGIC: