Android USB devices (eg. /sys/class/android_usb/android0/)

What:		/sys/class/android_usb/<android_device>/state
Date:		Feb 2024
Contact:	Neill Kapron <nkapron@google.com>
Description:
		The state of the USB connection. This attribute is likely
		redundant with the /sys/class/UDC/state attribute, and should
		be deprecated/removed when userspace can be refactored.
		Change on the state will also generate uevent KOBJ_CHANGE on
		the port with the new state included in the message as
		"USB_STATE=<STATE>". Note this is not the correct usage of
		uevents, but necessary due to the requirement to maintaine
		userspace API compatibility.

		Valid values: CONNECTED, DISCONNECTED, CONFIGURED

Android USB MIDI Function devices (eg. /sys/class/android_usb/androidN/f_midi/)

What:		/sys/class/android_usb/<android_device>/f_midi/alsa
Date:		Feb 2024
Contact		Neill Kapron <nkapron@google.com>
Description:
		The PCM card and device numbers created by the f_midi driver.
		This is not the correct use of sysfs due to passing multiple
		values through a single file, which is directly against the
		"one value per file" nature of sysfs, however Android userspace
		code currently relies on this functionality as-is.

		Valid values: card and device numbers in the format of
		<PCM_card_number> <device number>", or "-1 -1" if the attr
		is read prior to binding the f_midi device.