staging: usb: gadget: Add FunctionFS support to Configurable Composite Gadget driver

Add FunctionFS support.
It allows certain USB functions to be provided from userspace, e.g. MTP,
PTP, adb.

The functions provided by the gadget itself are enumerated in
/sys/class/ccg0/functions. The functions which can be supplied
from userspace must be enumerated in /sys/class/ccg0/f_fs/user_functions.
No other userspace functions can be used than specified in the above mentioned
file, but just specifying them there is not enough to activate them.
The userspace functions in order to be activated need also be enumerated
in /sys/class/ccg0/functions.

An example sequence of operations can be as follows:

$ echo 0 > /sys/class/ccg_usb/ccg0/enable

$ echo -n 0x2d01 > /sys/module/g_ccg/parameters/idProduct
$ echo -n MyDevice > /sys/module/g_ccg/parameters/iSerialNumber
$ echo -n 0x1d6b > /sys/module/g_ccg/parameters/idVendor
$ echo -n Manufacturer > /sys/module/g_ccg/parameters/iManufacturer
$ echo -n Product > /sys/module/g_ccg/parameters/iProduct
$ echo -n bcdDevice > /sys/module/g_ccg/parameters/bcdDevice

$ echo adb,mtp,ptp > /sys/class/ccg_usb/ccg0/f_fs/user_functions
$ echo mass_storage,ptp > /sys/class/ccg_usb/ccg0/functions
$ echo /file.img > /sys/class/ccg_usb/ccg0/f_mass_storage/lun/file

$ mkdir -p /dev/usbgadget/ptp
$ mount -t functionfs ptp /dev/usbgadget/ptp
$ ./ptp &

$ echo 1 > /sys/class/ccg_usb/ccg0/enable

The above example declares that adb, mtp and ptp functions can be supplied
from userspace through FunctionFS. But of them all only ptp is actually
activated, together with mass_storage, the latter being implemented in
the gadget itself (in kernel, not in userspace). The list of functions
can be modified at runtime while the gadget is not enabled, that is,
after

$ echo 0 > /sys/class/ccg_usb/ccg0/enable

The FunctionFS function is implicitly handled by the gadget, that is,
if a userspace function name is provided in
/sys/class/ccg_usb/ccg0/functions, then the FunctionFS function
is activated.
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ccg/sysfs-class-ccg_usb

@@ -22,7 +22,9 @@ KernelVersion:	3.4
 Contact:	linux-usb@vger.kernel.org
 Description:
 		A comma-separated list of USB function names to be activated
-		in this ccg gadget.
+		in this ccg gadget. It includes both the functions provided
+		in-kernel by the ccg gadget and the functions provided from
+		userspace through FunctionFS.
 
 What:		/sys/class/ccg_usb/ccgX/enable
 Date:		May 2012
@@ -58,6 +60,34 @@ Contact:	linux-usb@vger.kernel.org
 Description:
 		Maximum number of the /dev/ttyGS<X> interface the driver uses.
 
+What:		/sys/class/ccg_usb/ccgX/f_fs
+Date:		May 2012
+KernelVersion:	3.4
+Contact:	linux-usb@vger.kernel.org
+Description:
+		The /sys/class/ccg_usb/ccgX/f_fs subdirectory
+		corresponds to the gadget's FunctionFS driver.
+
+What:		/sys/class/ccg_usb/ccgX/f_fs/user_functions
+Date:		May 2012
+KernelVersion:	3.4
+Contact:	linux-usb@vger.kernel.org
+Description:
+		A comma-separeted list of USB function names to be supported
+		from userspace. No other userspace FunctionFS functions can
+		be supported than listed here. However, the actual activation
+		of these functions is still done through
+		/sys/class/ccg_usb/ccgX/functions, where it is possible
+		to specify any subset (including maximum and empty) of
+		/sys/class/ccg_usb/ccgX/f_fs/user_functions.
+
+What:		/sys/class/ccg_usb/ccgX/f_fs/max_user_functions
+Date:		May 2012
+KernelVersion:	3.4
+Contact:	linux-usb@vger.kernel.org
+Description:
+		Maximum number of USB functions to be supported from userspace.
+
 What:		/sys/class/ccg_usb/ccgX/f_rndis
 Date:		May 2012
 KernelVersion:	3.4