USB: f_fs: the FunctionFS driver

The FunctionFS is a USB composite function that can be used
with the composite framework to create an USB gadget.

>From kernel point of view it is just a composite function with
some unique behaviour.  It may be added to an USB
configuration only after the user space driver has registered
by writing descriptors and strings (the user space program has
to provide the same information that kernel level composite
functions provide when they are added to the configuration).

>From user space point of view it is a file system which when
mounted provide an "ep0" file.  User space driver need to
write descriptors and strings to that file.  It does not need
to worry about endpoints, interfaces or strings numbers but
simply provide descriptors such as if the function was the
only one (endpoints and strings numbers starting from one and
interface numbers starting from core).  The FunctionFS changes
numbers of those as needed also handling situation when
numbers differ in different configurations.

When descriptors and strings are written "ep#" files appear
(one for each declared endpoint) which handle communication on
a single endpoint.  Again, FunctionFS takes care of the real
numbers and changing of the configuration (which means that
"ep1" file may be really mapped to (say) endpoint 3 (and when
configuration changes to (say) endpoint 2)).  "ep0" is used
for receiving events and handling setup requests.

When all files are closed the function disables itself.
Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/usb/functionfs.h

+#ifndef __LINUX_FUNCTIONFS_H__
+#define __LINUX_FUNCTIONFS_H__ 1
+
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#include <linux/usb/ch9.h>
+
+
+enum {
+	FUNCTIONFS_DESCRIPTORS_MAGIC = 1,
+	FUNCTIONFS_STRINGS_MAGIC     = 2
+};
+
+
+#ifndef __KERNEL__
+
+/* Descriptor of an non-audio endpoint */
+struct usb_endpoint_descriptor_no_audio {
+	__u8  bLength;
+	__u8  bDescriptorType;
+
+	__u8  bEndpointAddress;
+	__u8  bmAttributes;
+	__le16 wMaxPacketSize;
+	__u8  bInterval;
+} __attribute__((packed));
+
+
+/*
+ * All numbers must be in little endian order.
+ */
+
+struct usb_functionfs_descs_head {
+	__le32 magic;
+	__le32 length;
+	__le32 fs_count;
+	__le32 hs_count;
+} __attribute__((packed));
+
+/*
+ * Descriptors format:
+ *
+ * | off | name      | type         | description                          |
+ * |-----+-----------+--------------+--------------------------------------|
+ * |   0 | magic     | LE32         | FUNCTIONFS_{FS,HS}_DESCRIPTORS_MAGIC |
+ * |   4 | lenght    | LE32         | length of the whole data chunk       |
+ * |   8 | fs_count  | LE32         | number of full-speed descriptors     |
+ * |  12 | hs_count  | LE32         | number of high-speed descriptors     |
+ * |  16 | fs_descrs | Descriptor[] | list of full-speed descriptors       |
+ * |     | hs_descrs | Descriptor[] | list of high-speed descriptors       |
+ *
+ * descs are just valid USB descriptors and have the following format:
+ *
+ * | off | name            | type | description              |
+ * |-----+-----------------+------+--------------------------|
+ * |   0 | bLength         | U8   | length of the descriptor |
+ * |   1 | bDescriptorType | U8   | descriptor type          |
+ * |   2 | payload         |      | descriptor's payload     |
+ */
+
+struct usb_functionfs_strings_head {
+	__le32 magic;
+	__le32 length;
+	__le32 str_count;
+	__le32 lang_count;
+} __attribute__((packed));
+
+/*
+ * Strings format:
+ *
+ * | off | name       | type                  | description                |
+ * |-----+------------+-----------------------+----------------------------|
+ * |   0 | magic      | LE32                  | FUNCTIONFS_STRINGS_MAGIC   |
+ * |   4 | length     | LE32                  | length of the data chunk   |
+ * |   8 | str_count  | LE32                  | number of strings          |
+ * |  12 | lang_count | LE32                  | number of languages        |
+ * |  16 | stringtab  | StringTab[lang_count] | table of strings per lang  |
+ *
+ * For each language there is one stringtab entry (ie. there are lang_count
+ * stringtab entires).  Each StringTab has following format:
+ *
+ * | off | name    | type              | description                        |
+ * |-----+---------+-------------------+------------------------------------|
+ * |   0 | lang    | LE16              | language code                      |
+ * |   2 | strings | String[str_count] | array of strings in given language |
+ *
+ * For each string ther is one strings entry (ie. there are str_count
+ * string entries).  Each String is a NUL terminated string encoded in
+ * UTF-8.
+ */
+
+#endif
+
+
+/*
+ * Events are delivered on the ep0 file descriptor, when the user mode driver
+ * reads from this file descriptor after writing the descriptors.  Don't
+ * stop polling this descriptor.
+ */
+
+enum usb_functionfs_event_type {
+	FUNCTIONFS_BIND,
+	FUNCTIONFS_UNBIND,
+
+	FUNCTIONFS_ENABLE,
+	FUNCTIONFS_DISABLE,
+
+	FUNCTIONFS_SETUP,
+
+	FUNCTIONFS_SUSPEND,
+	FUNCTIONFS_RESUME
+};
+
+/* NOTE:  this structure must stay the same size and layout on
+ * both 32-bit and 64-bit kernels.
+ */
+struct usb_functionfs_event {
+	union {
+		/* SETUP: packet; DATA phase i/o precedes next event
+		 *(setup.bmRequestType & USB_DIR_IN) flags direction */
+		struct usb_ctrlrequest	setup;
+	} __attribute__((packed)) u;
+
+	/* enum usb_functionfs_event_type */
+	__u8				type;
+	__u8				_pad[3];
+} __attribute__((packed));
+
+
+/* Endpoint ioctls */
+/* The same as in gadgetfs */
+
+/* IN transfers may be reported to the gadget driver as complete
+ *	when the fifo is loaded, before the host reads the data;
+ * OUT transfers may be reported to the host's "client" driver as
+ *	complete when they're sitting in the FIFO unread.
+ * THIS returns how many bytes are "unclaimed" in the endpoint fifo
+ * (needed for precise fault handling, when the hardware allows it)
+ */
+#define	FUNCTIONFS_FIFO_STATUS	_IO('g', 1)
+
+/* discards any unclaimed data in the fifo. */
+#define	FUNCTIONFS_FIFO_FLUSH	_IO('g', 2)
+
+/* resets endpoint halt+toggle; used to implement set_interface.
+ * some hardware (like pxa2xx) can't support this.
+ */
+#define	FUNCTIONFS_CLEAR_HALT	_IO('g', 3)
+
+/* Specific for functionfs */
+
+/*
+ * Returns reverse mapping of an interface.  Called on EP0.  If there
+ * is no such interface returns -EDOM.  If function is not active
+ * returns -ENODEV.
+ */
+#define	FUNCTIONFS_INTERFACE_REVMAP	_IO('g', 128)
+
+/*
+ * Returns real bEndpointAddress of an endpoint.  If function is not
+ * active returns -ENODEV.
+ */
+#define	FUNCTIONFS_ENDPOINT_REVMAP	_IO('g', 129)
+
+
+#ifdef __KERNEL__
+
+struct ffs_data;
+struct usb_composite_dev;
+struct usb_configuration;
+
+
+static int  functionfs_init(void) __attribute__((warn_unused_result));
+static void functionfs_cleanup(void);
+
+static int functionfs_bind(struct ffs_data *ffs, struct usb_composite_dev *cdev)
+	__attribute__((warn_unused_result, nonnull));
+static void functionfs_unbind(struct ffs_data *ffs)
+	__attribute__((nonnull));
+
+static int functionfs_add(struct usb_composite_dev *cdev,
+			  struct usb_configuration *c,
+			  struct ffs_data *ffs)
+	__attribute__((warn_unused_result, nonnull));
+
+
+static int functionfs_ready_callback(struct ffs_data *ffs)
+	__attribute__((warn_unused_result, nonnull));
+static void functionfs_closed_callback(struct ffs_data *ffs)
+	__attribute__((nonnull));
+static int functionfs_check_dev_callback(const char *dev_name)
+	__attribute__((warn_unused_result, nonnull));
+
+
+#endif
+
+#endif