USB: gmidi: New USB MIDI Gadget class driver.

This driver is glue between the USB gadget interface
and the ALSA MIDI interface. It allows us to appear
as a MIDI Streaming device to a host system on the
other end of a USB cable.

This includes linux/usb/audio.h and linux/usb/midi.h
containing definitions from the relevant USB specifications
for USB audio and USB MIDI devices.

The following changes have been made since the first RFC
posting:

* Bug fixes to endpoint handling.
* Workaround for USB_REQ_SET_CONFIGURATION handling,
  not understood yet.
* Added SND and SND_RAWMIDI dependencies in Kconfig.
* Moved usb_audio.h and usb_midi.h to usb/*.h
* Added module parameters for ALSA card index and id.
* Added module parameters for USB descriptor IDs and strings.
* Removed some unneeded stuff inherited from zero.c, more to go.
* Provide DECLARE_* macros for the variable-length structs.
* Use kmalloc instead of usb_ep_alloc_buffer.
* Limit source to 80 columns.
* Return actual error code instead of -ENOMEM in a few places.

Signed-off-by: Ben Williamson <ben.williamson@greyinnovation.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/usb/audio.h

@@ -0,0 +1,53 @@
+/*
+ * <linux/usb/audio.h> -- USB Audio definitions.
+ *
+ * Copyright (C) 2006 Thumtronics Pty Ltd.
+ * Developed for Thumtronics by Grey Innovation
+ * Ben Williamson <ben.williamson@greyinnovation.com>
+ *
+ * This software is distributed under the terms of the GNU General Public
+ * License ("GPL") version 2, as published by the Free Software Foundation.
+ *
+ * This file holds USB constants and structures defined
+ * by the USB Device Class Definition for Audio Devices.
+ * Comments below reference relevant sections of that document:
+ *
+ * http://www.usb.org/developers/devclass_docs/audio10.pdf
+ */
+
+#ifndef __LINUX_USB_AUDIO_H
+#define __LINUX_USB_AUDIO_H
+
+#include <linux/types.h>
+
+/* A.2 Audio Interface Subclass Codes */
+#define USB_SUBCLASS_AUDIOCONTROL	0x01
+#define USB_SUBCLASS_AUDIOSTREAMING	0x02
+#define USB_SUBCLASS_MIDISTREAMING	0x03
+
+/* 4.3.2  Class-Specific AC Interface Descriptor */
+struct usb_ac_header_descriptor {
+	__u8  bLength;			// 8+n
+	__u8  bDescriptorType;		// USB_DT_CS_INTERFACE
+	__u8  bDescriptorSubtype;	// USB_MS_HEADER
+	__le16 bcdADC;			// 0x0100
+	__le16 wTotalLength;		// includes Unit and Terminal desc.
+	__u8  bInCollection;		// n
+	__u8  baInterfaceNr[];		// [n]
+} __attribute__ ((packed));
+
+#define USB_DT_AC_HEADER_SIZE(n)	(8+(n))
+
+/* As above, but more useful for defining your own descriptors: */
+#define DECLARE_USB_AC_HEADER_DESCRIPTOR(n) 			\
+struct usb_ac_header_descriptor_##n {				\
+	__u8  bLength;						\
+	__u8  bDescriptorType;					\
+	__u8  bDescriptorSubtype;				\
+	__le16 bcdADC;						\
+	__le16 wTotalLength;					\
+	__u8  bInCollection;					\
+	__u8  baInterfaceNr[n];					\
+} __attribute__ ((packed))
+
+#endif