xref: /linux/Documentation/usb/gadget-testing.rst (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)

==============
Gadget Testing
==============

This file summarizes information on basic testing of USB functions
provided by gadgets.

.. contents

   1. ACM function
   2. ECM function
   3. ECM subset function
   4. EEM function
   5. FFS function
   6. HID function
   7. LOOPBACK function
   8. MASS STORAGE function
   9. MIDI function
   10. NCM function
   11. OBEX function
   12. PHONET function
   13. RNDIS function
   14. SERIAL function
   15. SOURCESINK function
   16. UAC1 function (legacy implementation)
   17. UAC2 function
   18. UVC function
   19. PRINTER function
   20. UAC1 function (new API)
   21. MIDI2 function


1. ACM function
===============

The function is provided by usb_f_acm.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "acm".
The ACM function provides just one attribute in its function directory:

	port_num

The attribute is read-only.

There can be at most 4 ACM/generic serial/OBEX ports in the system.


Testing the ACM function
------------------------

On the host::

	cat > /dev/ttyACM<X>

On the device::

	cat /dev/ttyGS<Y>

then the other way round

On the device::

	cat > /dev/ttyGS<Y>

On the host::

	cat /dev/ttyACM<X>

2. ECM function
===============

The function is provided by usb_f_ecm.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "ecm".
The ECM function provides these attributes in its function directory:

	=============== ==================================================
	ifname		network device interface name associated with this
			function instance
	qmult		queue length multiplier for high and super speed
	host_addr	MAC address of host's end of this
			Ethernet over USB link
	dev_addr	MAC address of device's end of this
			Ethernet over USB link
	=============== ==================================================

and after creating the functions/ecm.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
The ifname can be written to if the function is not bound. A write must be an
interface pattern such as "usb%d", which will cause the net core to choose the
next free usbX interface. By default, it is set to "usb%d".

Testing the ECM function
------------------------

Configure IP addresses of the device and the host. Then:

On the device::

	ping <host's IP>

On the host::

	ping <device's IP>

3. ECM subset function
======================

The function is provided by usb_f_ecm_subset.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "geth".
The ECM subset function provides these attributes in its function directory:

	=============== ==================================================
	ifname		network device interface name associated with this
			function instance
	qmult		queue length multiplier for high and super speed
	host_addr	MAC address of host's end of this
			Ethernet over USB link
	dev_addr	MAC address of device's end of this
			Ethernet over USB link
	=============== ==================================================

and after creating the functions/ecm.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
The ifname can be written to if the function is not bound. A write must be an
interface pattern such as "usb%d", which will cause the net core to choose the
next free usbX interface. By default, it is set to "usb%d".

Testing the ECM subset function
-------------------------------

Configure IP addresses of the device and the host. Then:

On the device::

	ping <host's IP>

On the host::

	ping <device's IP>

4. EEM function
===============

The function is provided by usb_f_eem.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "eem".
The EEM function provides these attributes in its function directory:

	=============== ==================================================
	ifname		network device interface name associated with this
			function instance
	qmult		queue length multiplier for high and super speed
	host_addr	MAC address of host's end of this
			Ethernet over USB link
	dev_addr	MAC address of device's end of this
			Ethernet over USB link
	=============== ==================================================

and after creating the functions/eem.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
The ifname can be written to if the function is not bound. A write must be an
interface pattern such as "usb%d", which will cause the net core to choose the
next free usbX interface. By default, it is set to "usb%d".

Testing the EEM function
------------------------

Configure IP addresses of the device and the host. Then:

On the device::

	ping <host's IP>

On the host::

	ping <device's IP>

5. FFS function
===============

The function is provided by usb_f_fs.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "ffs".
The function directory is intentionally empty and not modifiable.

After creating the directory there is a new instance (a "device") of FunctionFS
available in the system. Once a "device" is available, the user should follow
the standard procedure for using FunctionFS (mount it, run the userspace
process which implements the function proper). The gadget should be enabled
by writing a suitable string to usb_gadget/<gadget>/UDC.

The FFS function provides just one attribute in its function directory:

	ready

The attribute is read-only and signals if the function is ready (1) to be
used, E.G. if userspace has written descriptors and strings to ep0, so
the gadget can be enabled.

Testing the FFS function
------------------------

On the device: start the function's userspace daemon, enable the gadget

On the host: use the USB function provided by the device

6. HID function
===============

The function is provided by usb_f_hid.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "hid".
The HID function provides these attributes in its function directory:

	=============== ===========================================
	protocol	HID protocol to use
	report_desc	data to be used in HID reports, except data
			passed with /dev/hidg<X>
	report_length	HID report length
	subclass	HID subclass to use
	=============== ===========================================

For a keyboard the protocol and the subclass are 1, the report_length is 8,
while the report_desc is::

  $ hd my_report_desc
  00000000  05 01 09 06 a1 01 05 07  19 e0 29 e7 15 00 25 01  |..........)...%.|
  00000010  75 01 95 08 81 02 95 01  75 08 81 03 95 05 75 01  |u.......u.....u.|
  00000020  05 08 19 01 29 05 91 02  95 01 75 03 91 03 95 06  |....).....u.....|
  00000030  75 08 15 00 25 65 05 07  19 00 29 65 81 00 c0     |u...%e....)e...|
  0000003f

Such a sequence of bytes can be stored to the attribute with echo::

  $ echo -ne \\x05\\x01\\x09\\x06\\xa1.....

Testing the HID function
------------------------

Device:

- create the gadget
- connect the gadget to a host, preferably not the one used
  to control the gadget
- run a program which writes to /dev/hidg<N>, e.g.
  a userspace program found in Documentation/usb/gadget_hid.rst::

	$ ./hid_gadget_test /dev/hidg0 keyboard

Host:

- observe the keystrokes from the gadget

7. LOOPBACK function
====================

The function is provided by usb_f_ss_lb.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "Loopback".
The LOOPBACK function provides these attributes in its function directory:

	=============== =======================
	qlen		depth of loopback queue
	bulk_buflen	buffer length
	=============== =======================

Testing the LOOPBACK function
-----------------------------

device: run the gadget

host: test-usb (tools/usb/testusb.c)

8. MASS STORAGE function
========================

The function is provided by usb_f_mass_storage.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "mass_storage".
The MASS STORAGE function provides these attributes in its directory:
files:

	=============== ==============================================
	stall		Set to permit function to halt bulk endpoints.
			Disabled on some USB devices known not to work
			correctly. You should set it to true.
	num_buffers	Number of pipeline buffers. Valid numbers
			are 2..4. Available only if
			CONFIG_USB_GADGET_DEBUG_FILES is set.
	=============== ==============================================

and a default lun.0 directory corresponding to SCSI LUN #0.

A new lun can be added with mkdir::

	$ mkdir functions/mass_storage.0/partition.5

Lun numbering does not have to be continuous, except for lun #0 which is
created by default. A maximum of 8 luns can be specified and they all must be
named following the <name>.<number> scheme. The numbers can be 0..8.
Probably a good convention is to name the luns "lun.<number>",
although it is not mandatory.

In each lun directory there are the following attribute files:

	=============== ==============================================
	file		The path to the backing file for the LUN.
			Required if LUN is not marked as removable.
	ro		Flag specifying access to the LUN shall be
			read-only. This is implied if CD-ROM emulation
			is enabled as well as when it was impossible
			to open "filename" in R/W mode.
	removable	Flag specifying that LUN shall be indicated as
			being removable.
	cdrom		Flag specifying that LUN shall be reported as
			being a CD-ROM.
	nofua		Flag specifying that FUA flag
			in SCSI WRITE(10,12)
	forced_eject	This write-only file is useful only when
			the function is active. It causes the backing
			file to be forcibly detached from the LUN,
			regardless of whether the host has allowed it.
			Any non-zero number of bytes written will
			result in ejection.
	=============== ==============================================

Testing the MASS STORAGE function
---------------------------------

device: connect the gadget, enable it
host: dmesg, see the USB drives appear (if system configured to automatically
mount)

9. MIDI function
================

The function is provided by usb_f_midi.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "midi".
The MIDI function provides these attributes in its function directory:

	=============== ====================================
	buflen		MIDI buffer length
	id		ID string for the USB MIDI adapter
	in_ports	number of MIDI input ports
	index		index value for the USB MIDI adapter
	out_ports	number of MIDI output ports
	qlen		USB read request queue length
	=============== ====================================

Testing the MIDI function
-------------------------

There are two cases: playing a mid from the gadget to
the host and playing a mid from the host to the gadget.

1) Playing a mid from the gadget to the host:

host::

  $ arecordmidi -l
   Port    Client name                      Port name
   14:0    Midi Through                     Midi Through Port-0
   24:0    MIDI Gadget                      MIDI Gadget MIDI 1
  $ arecordmidi -p 24:0 from_gadget.mid

gadget::

  $ aplaymidi -l
   Port    Client name                      Port name
   20:0    f_midi                           f_midi

  $ aplaymidi -p 20:0 to_host.mid

2) Playing a mid from the host to the gadget

gadget::

  $ arecordmidi -l
   Port    Client name                      Port name
   20:0    f_midi                           f_midi

  $ arecordmidi -p 20:0 from_host.mid

host::

  $ aplaymidi -l
   Port    Client name                      Port name
   14:0    Midi Through                     Midi Through Port-0
   24:0    MIDI Gadget                      MIDI Gadget MIDI 1

  $ aplaymidi -p24:0 to_gadget.mid

The from_gadget.mid should sound identical to the to_host.mid.

The from_host.id should sound identical to the to_gadget.mid.

MIDI files can be played to speakers/headphones with e.g. timidity installed::

  $ aplaymidi -l
   Port    Client name                      Port name
   14:0    Midi Through                     Midi Through Port-0
   24:0    MIDI Gadget                      MIDI Gadget MIDI 1
  128:0    TiMidity                         TiMidity port 0
  128:1    TiMidity                         TiMidity port 1
  128:2    TiMidity                         TiMidity port 2
  128:3    TiMidity                         TiMidity port 3

  $ aplaymidi -p 128:0 file.mid

MIDI ports can be logically connected using the aconnect utility, e.g.::

  $ aconnect 24:0 128:0 # try it on the host

After the gadget's MIDI port is connected to timidity's MIDI port,
whatever is played at the gadget side with aplaymidi -l is audible
in host's speakers/headphones.

10. NCM function
================

The function is provided by usb_f_ncm.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "ncm".
The NCM function provides these attributes in its function directory:

	======================= ==================================================
	ifname			network device interface name associated with this
				function instance
	qmult			queue length multiplier for high and super speed
	host_addr		MAC address of host's end of this
				Ethernet over USB link
	dev_addr		MAC address of device's end of this
				Ethernet over USB link
	max_segment_size	Segment size required for P2P connections. This
				will set MTU to 14 bytes
	======================= ==================================================

and after creating the functions/ncm.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
The ifname can be written to if the function is not bound. A write must be an
interface pattern such as "usb%d", which will cause the net core to choose the
next free usbX interface. By default, it is set to "usb%d".

Testing the NCM function
------------------------

Configure IP addresses of the device and the host. Then:

On the device::

	ping <host's IP>

On the host::

	ping <device's IP>

11. OBEX function
=================

The function is provided by usb_f_obex.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "obex".
The OBEX function provides just one attribute in its function directory:

	port_num

The attribute is read-only.

There can be at most 4 ACM/generic serial/OBEX ports in the system.

Testing the OBEX function
-------------------------

On device::

	seriald -f /dev/ttyGS<Y> -s 1024

On host::

	serialc -v <vendorID> -p <productID> -i<interface#> -a1 -s1024 \
                -t<out endpoint addr> -r<in endpoint addr>

where seriald and serialc are Felipe's utilities found here:

	https://github.com/felipebalbi/usb-tools.git master

12. PHONET function
===================

The function is provided by usb_f_phonet.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "phonet".
The PHONET function provides just one attribute in its function directory:

	=============== ==================================================
	ifname		network device interface name associated with this
			function instance
	=============== ==================================================

Testing the PHONET function
---------------------------

It is not possible to test the SOCK_STREAM protocol without a specific piece
of hardware, so only SOCK_DGRAM has been tested. For the latter to work,
in the past I had to apply the patch mentioned here:

http://www.spinics.net/lists/linux-usb/msg85689.html

These tools are required:

git://git.gitorious.org/meego-cellular/phonet-utils.git

On the host::

	$ ./phonet -a 0x10 -i usbpn0
	$ ./pnroute add 0x6c usbpn0
	$./pnroute add 0x10 usbpn0
	$ ifconfig usbpn0 up

On the device::

	$ ./phonet -a 0x6c -i upnlink0
	$ ./pnroute add 0x10 upnlink0
	$ ifconfig upnlink0 up

Then a test program can be used::

	http://www.spinics.net/lists/linux-usb/msg85690.html

On the device::

	$ ./pnxmit -a 0x6c -r

On the host::

	$ ./pnxmit -a 0x10 -s 0x6c

As a result some data should be sent from host to device.
Then the other way round:

On the host::

	$ ./pnxmit -a 0x10 -r

On the device::

	$ ./pnxmit -a 0x6c -s 0x10

13. RNDIS function
==================

The function is provided by usb_f_rndis.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "rndis".
The RNDIS function provides these attributes in its function directory:

	=============== ==================================================
	ifname		network device interface name associated with this
			function instance
	qmult		queue length multiplier for high and super speed
	host_addr	MAC address of host's end of this
			Ethernet over USB link
	dev_addr	MAC address of device's end of this
			Ethernet over USB link
	=============== ==================================================

and after creating the functions/rndis.<instance name> they contain default
values: qmult is 5, dev_addr and host_addr are randomly selected.
The ifname can be written to if the function is not bound. A write must be an
interface pattern such as "usb%d", which will cause the net core to choose the
next free usbX interface. By default, it is set to "usb%d".

Testing the RNDIS function
--------------------------

Configure IP addresses of the device and the host. Then:

On the device::

	ping <host's IP>

On the host::

	ping <device's IP>

14. SERIAL function
===================

The function is provided by usb_f_gser.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "gser".
The SERIAL function provides just one attribute in its function directory:

	port_num

The attribute is read-only.

There can be at most 4 ACM/generic serial/OBEX ports in the system.

Testing the SERIAL function
---------------------------

On host::

	insmod usbserial
	echo VID PID >/sys/bus/usb-serial/drivers/generic/new_id

On host::

	cat > /dev/ttyUSB<X>

On target::

	cat /dev/ttyGS<Y>

then the other way round

On target::

	cat > /dev/ttyGS<Y>

On host::

	cat /dev/ttyUSB<X>

15. SOURCESINK function
=======================

The function is provided by usb_f_ss_lb.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "SourceSink".
The SOURCESINK function provides these attributes in its function directory:

	=============== ==================================
	pattern		0 (all zeros), 1 (mod63), 2 (none)
	isoc_interval	1..16
	isoc_maxpacket	0 - 1023 (fs), 0 - 1024 (hs/ss)
	isoc_mult	0..2 (hs/ss only)
	isoc_maxburst	0..15 (ss only)
	bulk_buflen	buffer length
	bulk_qlen	depth of queue for bulk
	iso_qlen	depth of queue for iso
	=============== ==================================

Testing the SOURCESINK function
-------------------------------

device: run the gadget

host: test-usb (tools/usb/testusb.c)


16. UAC1 function (legacy implementation)
=========================================

The function is provided by usb_f_uac1_legacy.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory
is "uac1_legacy".
The uac1 function provides these attributes in its function directory:

	=============== ====================================
	audio_buf_size	audio buffer size
	fn_cap		capture pcm device file name
	fn_cntl		control device file name
	fn_play		playback pcm device file name
	req_buf_size	ISO OUT endpoint request buffer size
	req_count	ISO OUT endpoint request count
	=============== ====================================

The attributes have sane default values.

Testing the UAC1 function
-------------------------

device: run the gadget

host::

	aplay -l # should list our USB Audio Gadget

17. UAC2 function
=================

The function is provided by usb_f_uac2.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "uac2".
The uac2 function provides these attributes in its function directory:

	================ ====================================================
	c_chmask         capture channel mask
	c_srate          list of capture sampling rates (comma-separated)
	c_ssize          capture sample size (bytes)
	c_sync           capture synchronization type (async/adaptive)
	c_mute_present   capture mute control enable
	c_volume_present capture volume control enable
	c_volume_min     capture volume control min value (in 1/256 dB)
	c_volume_max     capture volume control max value (in 1/256 dB)
	c_volume_res     capture volume control resolution (in 1/256 dB)
	c_hs_bint        capture bInterval for HS/SS (1-4: fixed, 0: auto)
	fb_max           maximum extra bandwidth in async mode
	p_chmask         playback channel mask
	p_srate          list of playback sampling rates (comma-separated)
	p_ssize          playback sample size (bytes)
	p_mute_present   playback mute control enable
	p_volume_present playback volume control enable
	p_volume_min     playback volume control min value (in 1/256 dB)
	p_volume_max     playback volume control max value (in 1/256 dB)
	p_volume_res     playback volume control resolution (in 1/256 dB)
	p_hs_bint        playback bInterval for HS/SS (1-4: fixed, 0: auto)
	req_number       the number of pre-allocated request for both capture
	                 and playback
	function_name    name of the interface
	c_terminal_type  code of the capture terminal type
	p_terminal_type  code of the playback terminal type
	================ ====================================================

The attributes have sane default values.

Testing the UAC2 function
-------------------------

device: run the gadget
host: aplay -l # should list our USB Audio Gadget

This function does not require real hardware support, it just
sends a stream of audio data to/from the host. In order to
actually hear something at the device side, a command similar
to this must be used at the device side::

	$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &

e.g.::

	$ arecord -f dat -t wav -D hw:CARD=UAC2Gadget,DEV=0 | \
	  aplay -D default:CARD=OdroidU3

18. UVC function
================

The function is provided by usb_f_uvc.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "uvc".
The uvc function provides these attributes in its function directory:

	=================== ================================================
	streaming_interval  interval for polling endpoint for data transfers
	streaming_maxburst  bMaxBurst for super speed companion descriptor
	streaming_maxpacket maximum packet size this endpoint is capable of
			    sending or receiving when this configuration is
			    selected
	function_name       name of the interface
	=================== ================================================

There are also "control" and "streaming" subdirectories, each of which contain
a number of their subdirectories. There are some sane defaults provided, but
the user must provide the following:

	================== ====================================================
	control header     create in control/header, link from control/class/fs
			   and/or control/class/ss
	streaming header   create in streaming/header, link from
			   streaming/class/fs and/or streaming/class/hs and/or
			   streaming/class/ss
	format description create in streaming/mjpeg and/or
			   streaming/uncompressed
	frame description  create in streaming/mjpeg/<format> and/or in
			   streaming/uncompressed/<format>
	================== ====================================================

Each frame description contains frame interval specification, and each
such specification consists of a number of lines with an interval value
in each line. The rules stated above are best illustrated with an example::

  # mkdir functions/uvc.usb0/control/header/h
  # cd functions/uvc.usb0/control/
  # ln -s header/h class/fs
  # ln -s header/h class/ss
  # mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p
  # cat <<EOF > functions/uvc.usb0/streaming/uncompressed/u/360p/dwFrameInterval
  666666
  1000000
  5000000
  EOF
  # cd $GADGET_CONFIGFS_ROOT
  # mkdir functions/uvc.usb0/streaming/header/h
  # cd functions/uvc.usb0/streaming/header/h
  # ln -s ../../uncompressed/u
  # cd ../../class/fs
  # ln -s ../../header/h
  # cd ../../class/hs
  # ln -s ../../header/h
  # cd ../../class/ss
  # ln -s ../../header/h


Testing the UVC function
------------------------

device: run the gadget, modprobe vivid::

  # uvc-gadget -u /dev/video<uvc video node #> -v /dev/video<vivid video node #>

where uvc-gadget is this program:
	http://git.ideasonboard.org/uvc-gadget.git

with these patches:

	http://www.spinics.net/lists/linux-usb/msg99220.html

host::

	luvcview -f yuv

19. PRINTER function
====================

The function is provided by usb_f_printer.ko module.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "printer".
The printer function provides these attributes in its function directory:

	==========	===========================================
	pnp_string	Data to be passed to the host in pnp string
	q_len		Number of requests per endpoint
	==========	===========================================

Testing the PRINTER function
----------------------------

The most basic testing:

device: run the gadget::

	# ls -l /devices/virtual/usb_printer_gadget/

should show g_printer<number>.

If udev is active, then /dev/g_printer<number> should appear automatically.

host:

If udev is active, then e.g. /dev/usb/lp0 should appear.

host->device transmission:

device::

	# cat /dev/g_printer<number>

host::

	# cat > /dev/usb/lp0

device->host transmission::

	# cat > /dev/g_printer<number>

host::

	# cat /dev/usb/lp0

More advanced testing can be done with the prn_example
described in Documentation/usb/gadget_printer.rst.


20. UAC1 function (virtual ALSA card, using u_audio API)
========================================================

The function is provided by usb_f_uac1.ko module.
It will create a virtual ALSA card and the audio streams are simply
sinked to and sourced from it.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "uac1".
The uac1 function provides these attributes in its function directory:

	================ ====================================================
	c_chmask         capture channel mask
	c_srate          list of capture sampling rates (comma-separated)
	c_ssize          capture sample size (bytes)
	c_mute_present   capture mute control enable
	c_volume_present capture volume control enable
	c_volume_min     capture volume control min value (in 1/256 dB)
	c_volume_max     capture volume control max value (in 1/256 dB)
	c_volume_res     capture volume control resolution (in 1/256 dB)
	p_chmask         playback channel mask
	p_srate          list of playback sampling rates (comma-separated)
	p_ssize          playback sample size (bytes)
	p_mute_present   playback mute control enable
	p_volume_present playback volume control enable
	p_volume_min     playback volume control min value (in 1/256 dB)
	p_volume_max     playback volume control max value (in 1/256 dB)
	p_volume_res     playback volume control resolution (in 1/256 dB)
	req_number       the number of pre-allocated requests for both capture
	                 and playback
	function_name    name of the interface
	================ ====================================================

The attributes have sane default values.

Testing the UAC1 function
-------------------------

device: run the gadget
host: aplay -l # should list our USB Audio Gadget

This function does not require real hardware support, it just
sends a stream of audio data to/from the host. In order to
actually hear something at the device side, a command similar
to this must be used at the device side::

	$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &

e.g.::

	$ arecord -f dat -t wav -D hw:CARD=UAC1Gadget,DEV=0 | \
	  aplay -D default:CARD=OdroidU3


21. MIDI2 function
==================

The function is provided by usb_f_midi2.ko module.
It will create a virtual ALSA card containing a UMP rawmidi device
where the UMP packet is looped back. In addition, a legacy rawmidi
device is created. The UMP rawmidi is bound with ALSA sequencer
clients, too.

Function-specific configfs interface
------------------------------------

The function name to use when creating the function directory is "midi2".
The midi2 function provides these attributes in its function directory
as the card top-level information:

	=============	=================================================
	process_ump	Bool flag to process UMP Stream messages (0 or 1)
	static_block	Bool flag for static blocks (0 or 1)
	iface_name	Optional interface name string
	=============	=================================================

The directory contains a subdirectory "ep.0", and this provides the
attributes for a UMP Endpoint (which is a pair of USB MIDI Endpoints):

	=============	=================================================
	protocol_caps	MIDI protocol capabilities;
			1: MIDI 1.0, 2: MIDI 2.0, or 3: both protocols
	protocol	Default MIDI protocol (either 1 or 2)
	ep_name		UMP Endpoint name string
	product_id	Product ID string
	manufacturer	Manufacture ID number (24 bit)
	family		Device family ID number (16 bit)
	model		Device model ID number (16 bit)
	sw_revision	Software revision (32 bit)
	=============	=================================================

Each Endpoint subdirectory contains a subdirectory "block.0", which
represents the Function Block for Block 0 information.
Its attributes are:

	=================	===============================================
	name			Function Block name string
	direction		Direction of this FB
				1: input, 2: output, or 3: bidirectional
	first_group		The first UMP Group number (0-15)
	num_groups		The number of groups in this FB (1-16)
	midi1_first_group	The first UMP Group number for MIDI 1.0 (0-15)
	midi1_num_groups	The number of groups for MIDI 1.0 (0-16)
	ui_hint			UI-hint of this FB
				0: unknown, 1: receiver, 2: sender, 3: both
	midi_ci_verison		Supported MIDI-CI version number (8 bit)
	is_midi1		Legacy MIDI 1.0 device (0-2)
				0: MIDI 2.0 device,
				1: MIDI 1.0 without restriction, or
				2: MIDI 1.0 with low speed
	sysex8_streams		Max number of SysEx8 streams (8 bit)
	active			Bool flag for FB activity (0 or 1)
	=================	===============================================

If multiple Function Blocks are required, you can add more Function
Blocks by creating subdirectories "block.<num>" with the corresponding
Function Block number (1, 2, ....). The FB subdirectories can be
dynamically removed, too. Note that the Function Block numbers must be
continuous.

Similarly, if you multiple UMP Endpoints are required, you can add
more Endpoints by creating subdirectories "ep.<num>". The number must
be continuous.

For emulating the old MIDI 2.0 device without UMP v1.1 support, pass 0
to `process_ump` flag. Then the whole UMP v1.1 requests are ignored.

Testing the MIDI2 function
--------------------------

On the device: run the gadget, and running::

  $ cat /proc/asound/cards

will show a new sound card containing a MIDI2 device.

OTOH, on the host::

  $ cat /proc/asound/cards

will show a new sound card containing either MIDI1 or MIDI2 device,
depending on the USB audio driver configuration.

On both, when ALSA sequencer is enabled on the host, you can find the
UMP MIDI client such as "MIDI 2.0 Gadget".

As the driver simply loops back the data, there is no need for a real
device just for testing.

For testing a MIDI input from the gadget to the host (e.g. emulating a
MIDI keyboard), you can send a MIDI stream like the following.

On the gadget::

  $ aconnect -o
  ....
  client 20: 'MIDI 2.0 Gadget' [type=kernel,card=1]
      0 'MIDI 2.0        '
      1 'Group 1 (MIDI 2.0 Gadget I/O)'
  $ aplaymidi -p 20:1 to_host.mid

On the host::

  $ aconnect -i
  ....
  client 24: 'MIDI 2.0 Gadget' [type=kernel,card=2]
      0 'MIDI 2.0        '
      1 'Group 1 (MIDI 2.0 Gadget I/O)'
  $ arecordmidi -p 24:1 from_gadget.mid

If you have a UMP-capable application, you can use the UMP port to
send/receive the raw UMP packets, too. For example, aseqdump program
with UMP support can receive from UMP port. On the host::

  $ aseqdump -u 2 -p 24:1
  Waiting for data. Press Ctrl+C to end.
  Source  Group    Event                  Ch  Data
   24:1   Group  0, Program change          0, program 0, Bank select 0:0
   24:1   Group  0, Channel pressure        0, value 0x80000000

For testing a MIDI output to the gadget to the host (e.g. emulating a
MIDI synth), it'll be just other way round.

On the gadget::

  $ arecordmidi -p 20:1 from_host.mid

On the host::

  $ aplaymidi -p 24:1 to_gadget.mid

The access to MIDI 1.0 on altset 0 on the host is supported, and it's
translated from/to UMP packets on the gadget. It's bound to only
Function Block 0.

The current operation mode can be observed in ALSA control element
"Operation Mode" for SND_CTL_IFACE_RAWMIDI.  For example::

  $ amixer -c1 contents
  numid=1,iface=RAWMIDI,name='Operation Mode'
    ; type=INTEGER,access=r--v----,values=1,min=0,max=2,step=0
    : values=2

where 0 = unused, 1 = MIDI 1.0 (altset 0), 2 = MIDI 2.0 (altset 1).
The example above shows it's running in 2, i.e. MIDI 2.0.