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diff --git a/kernel/Documentation/usb/gadget_multi.txt b/kernel/Documentation/usb/gadget_multi.txt new file mode 100644 index 000000000..7d66a8636 --- /dev/null +++ b/kernel/Documentation/usb/gadget_multi.txt @@ -0,0 +1,150 @@ + -*- org -*- + +* 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 two 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 much 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]] |