ALSA: usb-audio: Add quirk for MOTU MicroBook II

Add an entry to the quirks-table to for usb-audio to recognize the
Microbook II (although it only exposes vendor interfaces). A simple boot
quirk is also implemented to set up the sample rate and  make sure that
no audio urbs are sent before the device is ready.

This patch only provides audio playback and capture at 96kHz sample
rate. Notice the following shortcomings:

- The sample rate is currently hardcoded to 96k although the device also
  supports 48k and 44.1k.

- The various mixer controls of the MicroBook are not made available.

- The keep-iface control should be on by default because the device
  shuts down whenever the altsetting is reset which is usually unwanted.
  (I don't know the best way to do this)

- The communication format used by the MicroBook for sample rate setting
  and also other setup has been reverse engineered by looking at the
  usbmon output while running the windows driver through virtualbox. In
  this patch the first byte of every message is set to \0 while in the
  observed communications the first byte acts as a "message-counter"
  increasing its value with every message sent. Leaving it at \0 does
  not seem to affect the device.

Signed-off-by: Manuel Reinhardt <manuel.rhdt@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index db114f3977e0..056af0a57b22 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -354,6 +354,10 @@ static int set_sync_ep_implicit_fb_quirk(struct snd_usb_substream *subs,
 		ep = 0x81;
 		ifnum = 1;
 		goto add_sync_ep_from_ifnum;
+	case USB_ID(0x07fd, 0x0004): /* MOTU MicroBook II */
+		ep = 0x84;
+		ifnum = 0;
+		goto add_sync_ep_from_ifnum;
 	}
 
 	if (attr == USB_ENDPOINT_SYNC_ASYNC &&