ChangeSet 1.1078.2.1, 2003/05/08 11:32:50-07:00, david-b@pacbell.net

[PATCH] USB Gadget API (1/6)

This patch createss <linux/usb_gadget.h>, the gadget API
and inlined implementation.

There's additional kerneldoc, which I won't submit at
this time, available.


diff -Nru a/include/linux/usb_gadget.h b/include/linux/usb_gadget.h
--- /dev/null	Wed Dec 31 16:00:00 1969
+++ b/include/linux/usb_gadget.h	Thu May  8 14:32:12 2003
@@ -0,0 +1,734 @@
+/*
+ * <linux/usb_gadget.h>
+ *
+ * We call the USB code inside a Linux-based peripheral device a "gadget"
+ * driver, except for the hardware-specific bus glue.  One USB host can
+ * master many USB gadgets, but the gadgets are only slaved to one host.
+ *
+ *
+ * (c) Copyright 2002-2003 by David Brownell
+ * All Rights Reserved.
+ *
+ * This software is licensed under the GNU GPL version 2.
+ *
+ * ALTERNATIVELY, the kernel API documentation which is included in this
+ * software may also be licenced under the "GNU Free Documentation
+ * License" (version 1.2 or, at your choice, any later version), when
+ * used as part of the "USB Gadget API for Linux" documentation.
+ */
+
+#ifndef __LINUX_USB_GADGET_H
+#define __LINUX_USB_GADGET_H
+
+#ifdef __KERNEL__
+
+struct usb_ep;
+
+/**
+ * struct usb_request - describes one i/o request
+ * @buf: Buffer used for data.  Always provide this; some controllers
+ * 	only use PIO, or don't use DMA for some endpoints.
+ * @dma: DMA address corresponding to 'buf'.  If you don't set this
+ * 	field, and the usb controller needs one, it is responsible
+ * 	for mapping and unmapping the buffer.
+ * @length: Length of that data
+ * @no_interrupt: If true, hints that no completion irq is needed.
+ *	Helpful sometimes with deep request queues.
+ * @zero: If true, when writing data, makes the last packet be "short"
+ *     by adding a zero length packet as needed;
+ * @short_not_ok: When reading data, makes short packets be
+ *     treated as errors (queue stops advancing till cleanup).
+ * @complete: Function called when request completes
+ * @context: For use by the completion callback
+ * @list: For use by the gadget driver.
+ * @status: Reports completion code, zero or a negative errno.
+ * 	Normally, faults block the transfer queue from advancing until
+ * 	the completion callback returns.
+ * 	Code "-ESHUTDOWN" indicates completion caused by device disconnect,
+ * 	or when the driver disabled the endpoint.
+ * @actual: Reports actual bytes transferred.  For reads (OUT
+ * 	transfers) this may be less than the requested length.  If the
+ * 	short_not_ok flag is set, short reads are treated as errors
+ * 	even when status otherwise indicates successful completion.
+ * 	Note that for writes (IN transfers) the data bytes may still
+ * 	reside in a device-side FIFO.
+ *
+ * These are allocated/freed through the endpoint they're used with.  The
+ * hardware's driver can add extra per-request data to the memory it returns,
+ * which often avoids separate memory allocations (potential failures),
+ * later when the request is queued.
+ *
+ * Request flags affect request handling, such as whether a zero length
+ * packet is written (the "zero" flag), whether a short read should be
+ * treated as an error (blocking request queue advance, the "short_not_ok"
+ * flag), or hinting that an interrupt is not required (the "no_interrupt"
+ * flag, for use with deep request queues).
+ *
+ * Bulk endpoints can use any size buffers, and can also be used for interrupt
+ * transfers. interrupt-only endpoints can be much less functional.
+ */
+	// NOTE this is analagous to 'struct urb' on the host side,
+	// except that it's thinner and promotes more pre-allocation.
+	//
+	// ISSUE should this be allocated through the device?
+
+struct usb_request {
+	void			*buf;
+	unsigned		length;
+	dma_addr_t		dma;
+
+	unsigned		no_interrupt : 1,
+				zero : 1,
+				short_not_ok : 1;
+
+	void			(*complete)(struct usb_ep *ep,
+					struct usb_request *req);
+	void			*context;
+	struct list_head	list;
+
+	int			status;
+	unsigned		actual;
+};
+
+/*-------------------------------------------------------------------------*/
+
+/* endpoint-specific parts of the api to the usb controller hardware.
+ * unlike the urb model, (de)multiplexing layers are not required.
+ * (so this api could slash overhead if used on the host side...)
+ *
+ * note that device side usb controllers commonly differ in how many
+ * endpoints they support, as well as their capabilities.
+ */
+struct usb_ep_ops {
+	int (*enable) (struct usb_ep *ep,
+		const struct usb_endpoint_descriptor *desc);
+	int (*disable) (struct usb_ep *ep);
+
+	struct usb_request *(*alloc_request) (struct usb_ep *ep,
+		int gfp_flags);
+	void (*free_request) (struct usb_ep *ep, struct usb_request *req);
+
+	void *(*alloc_buffer) (struct usb_ep *ep, unsigned bytes,
+		dma_addr_t *dma, int gfp_flags);
+	void (*free_buffer) (struct usb_ep *ep, void *buf, dma_addr_t dma,
+		unsigned bytes);
+	// NOTE:  on 2.5, drivers may also use dma_map() and
+	// dma_sync_single() to manage dma overhead. 
+
+	int (*queue) (struct usb_ep *ep, struct usb_request *req,
+		int gfp_flags);
+	int (*dequeue) (struct usb_ep *ep, struct usb_request *req);
+
+	int (*set_halt) (struct usb_ep *ep, int value);
+	int (*fifo_status) (struct usb_ep *ep);
+	void (*fifo_flush) (struct usb_ep *ep);
+};
+
+/**
+ * struct usb_ep - device side representation of USB endpoint
+ * @name:identifier for the endpoint, such as "ep-a" or "ep9in-bulk"
+ * @ep_list:the gadget's ep_list holds all of its endpoints
+ * @maxpacket:the maximum packet size used on this endpoint, as
+ * 	configured when the endpoint was enabled.
+ * @driver_data:for use by the gadget driver.  all other fields are
+ * 	read-only to gadget drivers.
+ *
+ * the bus controller driver lists all the general purpose endpoints in
+ * gadget->ep_list.  the control endpoint (gadget->ep0) is not in that list,
+ * and is accessed only in response to a driver setup() callback.
+ */
+struct usb_ep {
+	void			*driver_data;
+
+	const char		*name;
+	const struct usb_ep_ops	*ops;
+	struct list_head	ep_list;
+	unsigned		maxpacket : 16;
+};
+
+/*-------------------------------------------------------------------------*/
+
+/**
+ * usb_ep_enable - configure endpoint, making it usable
+ * @ep:the endpoint being configured.  may not be the endpoint named "ep0".
+ * 	drivers discover endpoints through the ep_list of a usb_gadget.
+ * @desc:descriptor for desired behavior.  caller guarantees this pointer
+ * 	remains valid until the endpoint is disabled; the data byte order
+ * 	is little-endian (usb-standard).
+ *
+ * when configurations are set, or when interface settings change, the driver
+ * will enable or disable the relevant endpoints.  while it is enabled, an
+ * endpoint may be used for i/o until the driver receives a disconnect() from
+ * the host or until the endpoint is disabled.
+ *
+ * the ep0 implementation (which calls this routine) must ensure that the
+ * hardware capabilities of each endpoint match the descriptor provided
+ * for it.  for example, an endpoint named "ep2in-bulk" would be usable
+ * for interrupt transfers as well as bulk, but it likely couldn't be used
+ * for iso transfers or for endpoint 14.  some endpoints are fully
+ * configurable, with more generic names like "ep-a".  (remember that for
+ * USB, "in" means "towards the USB master".)
+ *
+ * returns zero, or a negative error code.
+ */
+static inline int
+usb_ep_enable (struct usb_ep *ep, const struct usb_endpoint_descriptor *desc)
+{
+	return ep->ops->enable (ep, desc);
+}
+
+/**
+ * usb_ep_disable - endpoint is no longer usable
+ * @ep:the endpoint being unconfigured.  may not be the endpoint named "ep0".
+ *
+ * no other task may be using this endpoint when this is called.
+ * any pending and uncompleted requests will complete with status
+ * indicating disconnect (-ESHUTDOWN) before this call returns.
+ * gadget drivers must call usb_ep_enable() again before queueing
+ * requests to the endpoint.
+ *
+ * returns zero, or a negative error code.
+ */
+static inline int
+usb_ep_disable (struct usb_ep *ep)
+{
+	return ep->ops->disable (ep);
+}
+
+/**
+ * usb_ep_alloc_request - allocate a request object to use with this endpoint
+ * @ep:the endpoint to be used with with the request
+ * @gfp_flags:GFP_* flags to use
+ *
+ * Request objects must be allocated with this call, since they normally
+ * need controller-specific setup and may even need endpoint-specific
+ * resources such as allocation of DMA descriptors.
+ * Requests may be submitted with usb_ep_queue(), and receive a single
+ * completion callback.  Free requests with usb_ep_free_request(), when
+ * they are no longer needed.
+ *
+ * Returns the request, or null if one could not be allocated.
+ */
+static inline struct usb_request *
+usb_ep_alloc_request (struct usb_ep *ep, int gfp_flags)
+{
+	return ep->ops->alloc_request (ep, gfp_flags);
+}
+
+/**
+ * usb_ep_free_request - frees a request object
+ * @ep:the endpoint associated with the request
+ * @req:the request being freed
+ *
+ * Reverses the effect of usb_ep_alloc_request().
+ * Caller guarantees the request is not queued, and that it will
+ * no longer be requeued (or otherwise used).
+ */
+static inline void
+usb_ep_free_request (struct usb_ep *ep, struct usb_request *req)
+{
+	ep->ops->free_request (ep, req);
+}
+
+/**
+ * usb_ep_alloc_buffer - allocate an I/O buffer
+ * @ep:the endpoint associated with the buffer
+ * @len:length of the desired buffer
+ * @dma:pointer to the buffer's DMA address; must be valid
+ * @gfp_flags:GFP_* flags to use
+ *
+ * Returns a new buffer, or null if one could not be allocated.
+ * The buffer is suitably aligned for dma, if that endpoint uses DMA,
+ * and the caller won't have to care about dma-inconsistency
+ * or any hidden "bounce buffer" mechanism.  No additional per-request
+ * DMA mapping will be required for such buffers.
+ * Free it later with usb_ep_free_buffer().
+ *
+ * You don't need to use this call to allocate I/O buffers unless you
+ * want to make sure drivers don't incur costs for such "bounce buffer"
+ * copies or per-request DMA mappings.
+ */
+static inline void *
+usb_ep_alloc_buffer (struct usb_ep *ep, unsigned len, dma_addr_t *dma,
+	int gfp_flags)
+{
+	return ep->ops->alloc_buffer (ep, len, dma, gfp_flags);
+}
+
+/**
+ * usb_ep_free_buffer - frees an i/o buffer
+ * @ep:the endpoint associated with the buffer
+ * @buf:CPU view address of the buffer
+ * @dma:the buffer's DMA address
+ * @len:length of the buffer
+ *
+ * reverses the effect of usb_ep_alloc_buffer().
+ * caller guarantees the buffer will no longer be accessed
+ */
+static inline void
+usb_ep_free_buffer (struct usb_ep *ep, void *buf, dma_addr_t dma, unsigned len)
+{
+	ep->ops->free_buffer (ep, buf, dma, len);
+}
+
+/**
+ * usb_ep_queue - queues (submits) an I/O request to an endpoint.
+ * @ep:the endpoint associated with the request
+ * @req:the request being submitted
+ * @gfp_flags: GFP_* flags to use in case the lower level driver couldn't
+ * 	pre-allocate all necessary memory with the request.
+ *
+ * This tells the device controller to perform the specified request through
+ * that endpoint (reading or writing a buffer).  When the request completes,
+ * including being canceled by usb_ep_dequeue(), the request's completion
+ * routine is called to return the request to the driver.  Any endpoint
+ * (except control endpoints like ep0) may have more than one transfer
+ * request queued; they complete in FIFO order.  Once a gadget driver
+ * submits a request, that request may not be examined or modified until it
+ * is given back to that driver through the completion callback.
+ *
+ * Each request is turned into one or more packets.  The controller driver
+ * never merges adjacent requests into the same packet.  OUT transfers
+ * will sometimes use data that's already buffered in the hardware.
+ *
+ * Bulk endpoints can queue any amount of data; the transfer is packetized
+ * automatically.  The last packet will be short if the request doesn't fill it
+ * out completely.  Zero length packets (ZLPs) should be avoided in portable
+ * protocols since not all usb hardware can successfully handle zero length
+ * packets.  (ZLPs may be explicitly written, and may be implicitly written if
+ * the request 'zero' flag is set.)  Bulk endpoints may also be used
+ * for interrupt transfers; but the reverse is not true, and some endpoints
+ * won't support every interrupt transfer.  (Such as 768 byte packets.)
+ *
+ * Interrupt-only endpoints are less functional than bulk endpoints, for
+ * example by not supporting queueing or not handling buffers that are
+ * larger than the endpoint's maxpacket size.  They may also treat data
+ * toggle differently.
+ *
+ * Control endpoints ... after getting a setup() callback, the driver queues
+ * one response (optional if it would be zero length).  That enables the
+ * status ack, after transfering data as specified in the response.  Setup
+ * functions may return negative error codes to generate protocol stalls.
+ *
+ * For periodic endpoints, like interrupt or isochronous ones, the usb host
+ * arranges to poll once per interval, and the gadget driver usually will
+ * have queued some data to transfer at that time.
+ *
+ * Returns zero, or a negative error code.  Endpoints that are not enabled,
+ * or which are enabled but halted, report errors; errors will also be
+ * reported when the usb peripheral is disconnected.
+ */
+static inline int
+usb_ep_queue (struct usb_ep *ep, struct usb_request *req, int gfp_flags)
+{
+	return ep->ops->queue (ep, req, gfp_flags);
+}
+
+/**
+ * usb_ep_dequeue - dequeues (cancels, unlinks) an I/O request from an endpoint
+ * @ep:the endpoint associated with the request
+ * @req:the request being canceled
+ *
+ * if the request is still active on the endpoint, it is dequeued and its
+ * completion routine is called (with status -ECONNRESET); else a negative
+ * error code is returned.
+ *
+ * note that some hardware can't clear out write fifos (to unlink the request
+ * at the head of the queue) except as part of disconnecting from usb.  such
+ * restrictions prevent drivers from supporting configuration changes,
+ * even to configuration zero (a "chapter 9" requirement).
+ */
+static inline int usb_ep_dequeue (struct usb_ep *ep, struct usb_request *req)
+{
+	return ep->ops->dequeue (ep, req);
+}
+
+/**
+ * usb_ep_set_halt - sets the endpoint halt feature.
+ * @ep: the non-isochronous endpoint being stalled
+ *
+ * Use this to stall an endpoint, perhaps as an error report.
+ * Except for control endpoints,
+ * the endpoint stays halted (will not stream any data) until the host
+ * clears this feature; drivers may need to empty the endpoint's request
+ * queue first, to make sure no inappropriate transfers happen.
+ *
+ * Returns zero, or a negative error code.  On success, this call sets
+ * underlying hardware state that blocks data transfers.
+ */
+static inline int
+usb_ep_set_halt (struct usb_ep *ep)
+{
+	return ep->ops->set_halt (ep, 1);
+}
+
+/**
+ * usb_ep_clear_halt - clears endpoint halt, and resets toggle
+ * @ep:the bulk or interrupt endpoint being reset
+ *
+ * use this when responding to the standard usb "set interface" request,
+ * for endpoints that aren't reconfigured, after clearing any other state
+ * in the endpoint's i/o queue.
+ *
+ * returns zero, or a negative error code.  on success, this call clears
+ * the underlying hardware state reflecting endpoint halt and data toggle.
+ */
+static inline int
+usb_ep_clear_halt (struct usb_ep *ep)
+{
+	return ep->ops->set_halt (ep, 0);
+}
+
+/**
+ * usb_ep_fifo_status - returns number of bytes in fifo, or error
+ * @ep: the endpoint whose fifo status is being checked.
+ *
+ * FIFO endpoints may have "unclaimed data" in them in certain cases,
+ * such as after aborted transfers.  Hosts may not have collected all
+ * the IN data written by the gadget driver, as reported by a request
+ * completion.  The gadget driver may not have collected all the data
+ * written OUT to it by the host.  Drivers that need precise handling for
+ * fault reporting or recovery may need to use this call.
+ *
+ * This returns the number of such bytes in the fifo, or a negative
+ * errno if the endpoint doesn't use a FIFO or doesn't support such
+ * precise handling.
+ */
+static inline int
+usb_ep_fifo_status (struct usb_ep *ep)
+{
+	if (ep->ops->fifo_status)
+		return ep->ops->fifo_status (ep);
+	else
+		return -EOPNOTSUPP;
+}
+
+/**
+ * usb_ep_fifo_flush - flushes contents of a fifo
+ * @ep: the endpoint whose fifo is being flushed.
+ *
+ * This call may be used to flush the "unclaimed data" that may exist in
+ * an endpoint fifo after abnormal transaction terminations.  The call
+ * must never be used except when endpoint is not being used for any
+ * protocol translation.
+ */
+static inline void
+usb_ep_fifo_flush (struct usb_ep *ep)
+{
+	if (ep->ops->fifo_flush)
+		ep->ops->fifo_flush (ep);
+}
+
+
+/*-------------------------------------------------------------------------*/
+
+struct usb_gadget;
+
+/* the rest of the api to the controller hardware: device operations,
+ * which don't involve endpoints (or i/o).
+ */
+struct usb_gadget_ops {
+	int	(*get_frame)(struct usb_gadget *);
+	int	(*wakeup)(struct usb_gadget *);
+	int	(*set_selfpowered) (struct usb_gadget *, int value);
+	int	(*ioctl)(struct usb_gadget *,
+				unsigned code, unsigned long param);
+};
+
+#if LINUX_VERSION_CODE > KERNEL_VERSION(2,5,50)
+#define	HAVE_DRIVER_MODEL
+#include <linux/device.h>
+#endif
+
+/**
+ * struct usb_gadget - represents a usb slave device
+ * @ep0: Endpoint zero, used when reading or writing responses to
+ * 	driver setup() requests
+ * @ep_list: List of other endpoints supported by the device.
+ * @speed: Speed of current connection to USB host.
+ * @name: Identifies the controller hardware type.  Used in diagnostics
+ * 	and sometimes configuration.
+ *
+ * Gadgets have a mostly-portable "gadget driver" implementing device
+ * functions, handling all usb configurations and interfaces.  They
+ * also have a hardware-specific driver (accessed through ops vectors),
+ * which insulates the gadget driver from hardware details and packages
+ * the hardware endpoints through generic i/o queues.
+ *
+ * Except for the driver data, all fields in this structure are
+ * read-only to the gadget driver.  That driver data is part of the
+ * "driver model" infrastructure in 2.5 (and later) kernels, and for
+ * earlier systems is grouped in a similar structure that's not known
+ * to the rest of the kernel.
+ */
+struct usb_gadget {
+	/* readonly to gadget driver */
+	const struct usb_gadget_ops	*ops;
+	struct usb_ep			*ep0;
+	struct list_head		ep_list;	/* of usb_ep */
+	enum usb_device_speed		speed;
+	const char			*name;
+
+#ifdef	HAVE_DRIVER_MODEL
+	/* with 2.5 "generic dma" api, use this to allocate dma-coherent
+	 * buffers or set up dma mappings.  or print diagnostics, etc.
+	 */
+	struct device			dev;
+#else
+	struct __gadget_device {
+		char			*bus_id;
+		void			*driver_data;
+	} dev;
+#endif
+};
+
+#ifdef	HAVE_DRIVER_MODEL
+static inline void set_gadget_data (struct usb_gadget *gadget, void *data)
+	{ dev_set_drvdata (&gadget->dev, data); }
+static inline void *get_gadget_data (struct usb_gadget *gadget)
+	{ return dev_get_drvdata (&gadget->dev); }
+
+#else
+static inline void set_gadget_data (struct usb_gadget *gadget, void *data)
+	{ gadget->dev.driver_data = data; }
+static inline void *get_gadget_data (struct usb_gadget *gadget)
+	{ return gadget->dev.driver_data; }
+
+#endif
+
+/* iterates the non-control endpoints; 'tmp' is a struct usb_ep pointer */
+#define gadget_for_each_ep(tmp,gadget) \
+	list_for_each_entry(tmp, &(gadget)->ep_list, ep_list)
+
+#ifndef list_for_each_entry
+/* not available in 2.4.18 */
+#define list_for_each_entry(pos, head, member)				\
+	for (pos = list_entry((head)->next, typeof(*pos), member),	\
+		     prefetch(pos->member.next);			\
+	     &pos->member != (head); 					\
+	     pos = list_entry(pos->member.next, typeof(*pos), member),	\
+		     prefetch(pos->member.next))
+#endif
+
+
+/**
+ * usb_gadget_frame_number - returns the current frame number
+ * @gadget: controller that reports the frame number
+ *
+ * Returns the usb frame number, normally eleven bits from a SOF packet,
+ * or negative errno if this device doesn't support this capability.
+ */
+static inline int usb_gadget_frame_number (struct usb_gadget *gadget)
+{
+	return gadget->ops->get_frame (gadget);
+}
+
+/**
+ * usb_gadget_wakeup - tries to wake up the host connected to this gadget
+ * @gadget: controller used to wake up the host
+ *
+ * Returns zero on success, else negative error code if the hardware
+ * doesn't support such attempts, or its support has not been enabled
+ * by the usb host.  Drivers must return device descriptors that report
+ * their ability to support this, or hosts won't enable it.
+ */
+static inline int usb_gadget_wakeup (struct usb_gadget *gadget)
+{
+	if (!gadget->ops->wakeup)
+		return -EOPNOTSUPP;
+	return gadget->ops->wakeup (gadget);
+}
+
+/**
+ * usb_gadget_set_selfpowered - sets the device selfpowered feature.
+ * @gadget:the device being declared as self-powered
+ *
+ * this affects the device status reported by the hardware driver
+ * to reflect that it now has a local power supply.
+ *
+ * returns zero on success, else negative errno.
+ */
+static inline int
+usb_gadget_set_selfpowered (struct usb_gadget *gadget)
+{
+	if (!gadget->ops->set_selfpowered)
+		return -EOPNOTSUPP;
+	return gadget->ops->set_selfpowered (gadget, 1);
+}
+
+/**
+ * usb_gadget_clear_selfpowered - clear the device selfpowered feature.
+ * @gadget:the device being declared as bus-powered
+ *
+ * this affects the device status reported by the hardware driver.
+ * some hardware may not support bus-powered operation, in which
+ * case this feature's value can never change.
+ *
+ * returns zero on success, else negative errno.
+ */
+static inline int
+usb_gadget_clear_selfpowered (struct usb_gadget *gadget)
+{
+	if (!gadget->ops->set_selfpowered)
+		return -EOPNOTSUPP;
+	return gadget->ops->set_selfpowered (gadget, 0);
+}
+
+
+/*-------------------------------------------------------------------------*/
+
+/**
+ * struct usb_gadget_driver - driver for usb 'slave' devices
+ * @function: String describing the gadget's function
+ * @speed: Highest speed the driver handles.
+ * @bind: Invoked when the driver is bound to a gadget, usually
+ * 	after registering the driver.
+ * 	At that point, ep0 is fully initialized, and ep_list holds
+ * 	the currently-available endpoints.
+ * 	Called in a context that permits sleeping.
+ * @setup: Invoked for ep0 control requests that aren't handled by
+ * 	the hardware level driver. Most calls must be handled by
+ * 	the gadget driver, including descriptor and configuration
+ * 	management.  The 16 bit members of the setup data are in
+ * 	cpu order. Called in_interrupt; this may not sleep.  Driver
+ *	queues a response to ep0, or returns negative to stall.
+ * @disconnect: Invoked after all transfers have been stopped,
+ * 	when the host is disconnected.  May be called in_interrupt; this
+ * 	may not sleep.
+ * @unbind: Invoked when the driver is unbound from a gadget,
+ * 	usually from rmmod (after a disconnect is reported).
+ * 	Called in a context that permits sleeping.
+ * @suspend: Invoked on USB suspend.  May be called in_interrupt.
+ * @resume: Invoked on USB resume.  May be called in_interrupt.
+ *
+ * Devices are disabled till a gadget driver successfully bind()s, which
+ * means the driver will handle setup() requests needed to enumerate (and
+ * meet "chapter 9" requirements) then do some useful work.
+ *
+ * Drivers use hardware-specific knowledge to configure the usb hardware.
+ * endpoint addressing is only one of several hardware characteristics that
+ * are in descriptors the ep0 implementation returns from setup() calls.
+ *
+ * Except for ep0 implementation, most driver code shouldn't need change to
+ * run on top of different usb controllers.  It'll use endpoints set up by
+ * that ep0 implementation.
+ *
+ * The usb controller driver handles a few standard usb requests.  Those
+ * include set_address, and feature flags for devices, interfaces, and
+ * endpoints (the get_status, set_feature, and clear_feature requests).
+ *
+ * Accordingly, the driver's setup() callback must always implement all
+ * get_descriptor requests, returning at least a device descriptor and
+ * a configuration descriptor.  Drivers must make sure the endpoint
+ * descriptors match any hardware constraints. Some hardware also constrains
+ * other descriptors. (The pxa250 allows only configurations 1, 2, or 3).
+ *
+ * The driver's setup() callback must also implement set_configuration,
+ * and should also implement set_interface, get_configuration, and
+ * get_interface.  Setting a configuration (or interface) is where
+ * endpoints should be activated or (config 0) shut down.
+ *
+ * (Note that only the default control endpoint is supported.  Neither
+ * hosts nor devices generally support control traffic except to ep0.)
+ *
+ * Most devices will ignore USB suspend/resume operations, and so will
+ * not provide those callbacks.  However, some may need to change modes
+ * when the host is not longer directing those activities.  For example,
+ * local controls (buttons, dials, etc) may need to be re-enabled since
+ * the (remote) host can't do that any longer. 
+ */
+struct usb_gadget_driver {
+	char			*function;
+	enum usb_device_speed	speed;
+	int			(*bind)(struct usb_gadget *);
+	void			(*unbind)(struct usb_gadget *);
+	int			(*setup)(struct usb_gadget *,
+					const struct usb_ctrlrequest *);
+	void			(*disconnect)(struct usb_gadget *);
+	void			(*suspend)(struct usb_gadget *);
+	void			(*resume)(struct usb_gadget *);
+
+	// FIXME support safe rmmod
+#ifdef	HAVE_DRIVER_MODEL
+	struct device_driver	driver;
+#else
+	struct __gadget_driver {
+		char		*name;
+		void		*driver_data;
+	} driver;
+#endif
+};
+
+
+
+/*-------------------------------------------------------------------------*/
+
+/* driver modules register and unregister, as usual.
+ * these calls must be made in a context that can sleep.
+ *
+ * these will usually be implemented directly by the hardware-dependent
+ * usb bus interface driver, which will only support a single driver.
+ */
+
+/**
+ * usb_gadget_register_driver - register a gadget driver
+ * @driver:the driver being registered
+ *
+ * Call this in your gadget driver's module initialization function,
+ * to tell the underlying usb controller driver about your driver.
+ * The driver's bind() function will be called to bind it to a
+ * gadget.  This function must be called in a context that can sleep.
+ */
+int usb_gadget_register_driver (struct usb_gadget_driver *driver);
+
+/**
+ * usb_gadget_unregister_driver - unregister a gadget driver
+ * @driver:the driver being unregistered
+ *
+ * Call this in your gadget driver's module cleanup function,
+ * to tell the underlying usb controller that your driver is
+ * going away.  If the controller is connected to a USB host,
+ * it will first disconnect().  The driver is also requested
+ * to unbind() and clean up any device state, before this procedure
+ * finally returns.
+ * This function must be called in a context that can sleep.
+ */
+int usb_gadget_unregister_driver (struct usb_gadget_driver *driver);
+
+/*-------------------------------------------------------------------------*/
+
+/* utility to simplify dealing with string descriptors */
+
+/**
+ * struct usb_string - wraps a C string and its USB id
+ * @id:the (nonzero) ID for this string
+ * @s:the string, in ISO-8859/1 characters
+ *
+ * If you're using usb_gadget_get_string(), use this to wrap a string
+ * together with its ID.
+ */
+struct usb_string {
+	u8			id;
+	const char		*s;
+};
+
+/**
+ * struct usb_gadget_strings - a set of USB strings in a given language
+ * @language:identifies the strings' language (0x0409 for en-us)
+ * @strings:array of strings with their ids
+ *
+ * If you're using usb_gadget_get_string(), use this to wrap all the
+ * strings for a given language.
+ */
+struct usb_gadget_strings {
+	u16			language;	/* 0x0409 for en-us */
+	struct usb_string	*strings;
+};
+
+/* put descriptor for string with that id into buf (buflen >= 256) */
+int usb_gadget_get_string (struct usb_gadget_strings *table, int id, u8 *buf);
+
+
+#endif  /* __KERNEL__ */
+
+#endif	/* __LINUX_USB_GADGET_H */