Documentation/usb/gadget_multi.rst - linux/kernel/git/dhowells/linux-fs - Git at Google


            
            ==============================

            
            Multifunction Composite Gadget

            
            ==============================


            Overview

            
            ========


            The Multifunction Composite Gadget (or g_multi) is a composite gadget

            
            that makes extensive use of the composite framework to provide

            
            a... multifunction gadget.


            In its standard configuration it provides a single USB configuration

            
            with RNDIS[1] (that is Ethernet), USB CDC[2] ACM (that is serial) and

            
            USB Mass Storage functions.


            A CDC ECM (Ethernet) function may be turned on via a Kconfig option

            
            and RNDIS can be turned off.  If they are both enabled the gadget will

            
            have two configurations -- one with RNDIS and another with CDC ECM[3].


            Please note that if you use non-standard configuration (that is enable

            
            CDC ECM) you may need to change vendor and/or product ID.


            Host drivers

            
            ============


            To make use of the gadget one needs to make it work on host side --

            
            without that there's no hope of achieving anything with the gadget.

            
            As one might expect, things one need to do very from system to system.


            Linux host drivers

            
            ------------------


            Since the gadget uses standard composite framework and appears as such

            
            to Linux host it does not need any additional drivers on Linux host

            
            side.  All the functions are handled by respective drivers developed

            
            for them.


            This is also true for two configuration set-up with RNDIS

            
            configuration being the first one.  Linux host will use the second

            
            configuration with CDC ECM which should work better under Linux.


            Windows host drivers

            
            --------------------


            For the gadget to work under Windows two conditions have to be met:


            Detecting as composite gadget

            
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


            First of all, Windows need to detect the gadget as an USB composite

            
            gadget which on its own have some conditions[4].  If they are met,

            
            Windows lets USB Generic Parent Driver[5] handle the device which then

            
            tries to match drivers for each individual interface (sort of, don't

            
            get into too many details).


            The good news is: you do not have to worry about most of the

            
            conditions!


            The only thing to worry is that the gadget has to have a single

            
            configuration so a dual RNDIS and CDC ECM gadget won't work unless you

            
            create a proper INF -- and of course, if you do submit it!


            Installing drivers for each function

            
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


            The other, trickier thing is making Windows install drivers for each

            
            individual function.


            For mass storage it is trivial since Windows detect it's an interface

            
            implementing USB Mass Storage class and selects appropriate driver.


            Things are harder with RDNIS and CDC ACM.


            RNDIS

            
            .....


            To make Windows select RNDIS drivers for the first function in the

            
            gadget, one needs to use the [[file:linux.inf]] file provided with this

            
            document.  It "attaches" Window's RNDIS driver to the first interface

            
            of the gadget.


            Please note, that while testing we encountered some issues[6] when

            
            RNDIS was not the first interface.  You do not need to worry abut it

            
            unless you are trying to develop your own gadget in which case watch

            
            out for this bug.


            CDC ACM

            
            .......


            Similarly, [[file:linux-cdc-acm.inf]] is provided for CDC ACM.


            Customising the gadget

            
            ......................


            If you intend to hack the g_multi gadget be advised that rearranging

            
            functions will obviously change interface numbers for each of the

            
            functionality.  As an effect provided INFs won't work since they have

            
            interface numbers hard-coded in them (it's not hard to change those

            
            though[7]).


            This also means, that after experimenting with g_multi and changing

            
            provided functions one should change gadget's vendor and/or product ID

            
            so there will be no collision with other customised gadgets or the

            
            original gadget.


            Failing to comply may cause brain damage after wondering for hours why

            
            things don't work as intended before realising Windows have cached

            
            some drivers information (changing USB port may sometimes help plus

            
            you might try using USBDeview[8] to remove the phantom device).


            INF testing

            
            ...........


            Provided INF files have been tested on Windows XP SP3, Windows Vista

            
            and Windows 7, all 32-bit versions.  It should work on 64-bit versions

            
            as well.  It most likely won't work on Windows prior to Windows XP

            
            SP2.


            Other systems

            
            -------------


            At this moment, drivers for any other systems have not been tested.

            
            Knowing how MacOS is based on BSD and BSD is an Open Source it is

            
            believed that it should (read: "I have no idea whether it will") work

            
            out-of-the-box.


            For more exotic systems I have even less to say...


            Any testing and drivers *are* *welcome*!


            Authors

            
            =======


            This document has been written by Michal Nazarewicz

            
            ([[mailto:mina86@mina86.com]]).  INF files have been hacked with

            
            support of Marek Szyprowski ([[mailto:m.szyprowski@samsung.com]]) and

            
            Xiaofan Chen ([[mailto:xiaofanc@gmail.com]]) basing on the MS RNDIS

            
            template[9], Microchip's CDC ACM INF file and David Brownell's

            
            ([[mailto:dbrownell@users.sourceforge.net]]) original INF files.


            Footnotes

            
            =========


            [1] Remote Network Driver Interface Specification,

            
            [[https://msdn.microsoft.com/en-us/library/ee484414.aspx]].


            [2] Communications Device Class Abstract Control Model, spec for this

            
            and other USB classes can be found at

            
            [[http://www.usb.org/developers/devclass_docs/]].


            [3] CDC Ethernet Control Model.


            [4] [[https://msdn.microsoft.com/en-us/library/ff537109(v=VS.85).aspx]]


            [5] [[https://msdn.microsoft.com/en-us/library/ff539234(v=VS.85).aspx]]


            [6] To put it in some other nice words, Windows failed to respond to

            
            any user input.


            [7] You may find [[http://www.cygnal.org/ubb/Forum9/HTML/001050.html]]

            
            useful.


            [8] https://www.nirsoft.net/utils/usb_devices_view.html


            [9] [[https://msdn.microsoft.com/en-us/library/ff570620.aspx]]
	==============================
	Multifunction Composite Gadget
	==============================

	Overview
	========

	The Multifunction Composite Gadget (or g_multi) is a composite gadget
	that makes extensive use of the composite framework to provide
	a... multifunction gadget.

	In its standard configuration it provides a single USB configuration
	with RNDIS[1] (that is Ethernet), USB CDC[2] ACM (that is serial) and
	USB Mass Storage functions.

	A CDC ECM (Ethernet) function may be turned on via a Kconfig option
	and RNDIS can be turned off. If they are both enabled the gadget will
	have two configurations -- one with RNDIS and another with CDC ECM[3].

	Please note that if you use non-standard configuration (that is enable
	CDC ECM) you may need to change vendor and/or product ID.

	Host drivers
	============

	To make use of the gadget one needs to make it work on host side --
	without that there's no hope of achieving anything with the gadget.
	As one might expect, things one need to do very from system to system.

	Linux host drivers
	------------------

	Since the gadget uses standard composite framework and appears as such
	to Linux host it does not need any additional drivers on Linux host
	side. All the functions are handled by respective drivers developed
	for them.

	This is also true for two configuration set-up with RNDIS
	configuration being the first one. Linux host will use the second
	configuration with CDC ECM which should work better under Linux.

	Windows host drivers
	--------------------

	For the gadget to work under Windows two conditions have to be met:

	Detecting as composite gadget
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	First of all, Windows need to detect the gadget as an USB composite
	gadget which on its own have some conditions[4]. If they are met,
	Windows lets USB Generic Parent Driver[5] handle the device which then
	tries to match drivers for each individual interface (sort of, don't
	get into too many details).

	The good news is: you do not have to worry about most of the
	conditions!

	The only thing to worry is that the gadget has to have a single
	configuration so a dual RNDIS and CDC ECM gadget won't work unless you
	create a proper INF -- and of course, if you do submit it!

	Installing drivers for each function
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	The other, trickier thing is making Windows install drivers for each
	individual function.

	For mass storage it is trivial since Windows detect it's an interface
	implementing USB Mass Storage class and selects appropriate driver.

	Things are harder with RDNIS and CDC ACM.

	RNDIS
	.....

	To make Windows select RNDIS drivers for the first function in the
	gadget, one needs to use the [[file:linux.inf]] file provided with this
	document. It "attaches" Window's RNDIS driver to the first interface
	of the gadget.

	Please note, that while testing we encountered some issues[6] when
	RNDIS was not the first interface. You do not need to worry abut it
	unless you are trying to develop your own gadget in which case watch
	out for this bug.

	CDC ACM
	.......

	Similarly, [[file:linux-cdc-acm.inf]] is provided for CDC ACM.

	Customising the gadget
	......................

	If you intend to hack the g_multi gadget be advised that rearranging
	functions will obviously change interface numbers for each of the
	functionality. As an effect provided INFs won't work since they have
	interface numbers hard-coded in them (it's not hard to change those
	though[7]).

	This also means, that after experimenting with g_multi and changing
	provided functions one should change gadget's vendor and/or product ID
	so there will be no collision with other customised gadgets or the
	original gadget.

	Failing to comply may cause brain damage after wondering for hours why
	things don't work as intended before realising Windows have cached
	some drivers information (changing USB port may sometimes help plus
	you might try using USBDeview[8] to remove the phantom device).

	INF testing
	...........

	Provided INF files have been tested on Windows XP SP3, Windows Vista
	and Windows 7, all 32-bit versions. It should work on 64-bit versions
	as well. It most likely won't work on Windows prior to Windows XP
	SP2.

	Other systems
	-------------

	At this moment, drivers for any other systems have not been tested.
	Knowing how MacOS is based on BSD and BSD is an Open Source it is
	believed that it should (read: "I have no idea whether it will") work
	out-of-the-box.

	For more exotic systems I have even less to say...

	Any testing and drivers are welcome!

	Authors
	=======

	This document has been written by Michal Nazarewicz
	([[mailto:mina86@mina86.com]]). INF files have been hacked with
	support of Marek Szyprowski ([[mailto:m.szyprowski@samsung.com]]) and
	Xiaofan Chen ([[mailto:xiaofanc@gmail.com]]) basing on the MS RNDIS
	template[9], Microchip's CDC ACM INF file and David Brownell's
	([[mailto:dbrownell@users.sourceforge.net]]) original INF files.

	Footnotes
	=========

	[1] Remote Network Driver Interface Specification,
	[[https://msdn.microsoft.com/en-us/library/ee484414.aspx]].

	[2] Communications Device Class Abstract Control Model, spec for this
	and other USB classes can be found at
	[[http://www.usb.org/developers/devclass_docs/]].

	[3] CDC Ethernet Control Model.

	[4] [[https://msdn.microsoft.com/en-us/library/ff537109(v=VS.85).aspx]]

	[5] [[https://msdn.microsoft.com/en-us/library/ff539234(v=VS.85).aspx]]

	[6] To put it in some other nice words, Windows failed to respond to
	any user input.

	[7] You may find [[http://www.cygnal.org/ubb/Forum9/HTML/001050.html]]
	useful.

	[8] https://www.nirsoft.net/utils/usb_devices_view.html

	[9] [[https://msdn.microsoft.com/en-us/library/ff570620.aspx]]