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 ==============================
 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 it's 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]]

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