1 files changed, 165 insertions, 0 deletions
diff --git a/Documentation/usb/gadget_multi.rst b/Documentation/usb/gadget_multi.rst
new file mode 100644
index 000000000000..9806b55af301
--- /dev/null
+++ b/Documentation/usb/gadget_multi.rst
@@ -0,0 +1,165 @@
+==============================
+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,
+[[http://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] [[http://msdn.microsoft.com/en-us/library/ff537109(v=VS.85).aspx]]
+
+[5] [[http://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] http://www.nirsoft.net/utils/usb_devices_view.html
+
+[9] [[http://msdn.microsoft.com/en-us/library/ff570620.aspx]]