path: root/include/linux/usb_gadget.h

/*
 * <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 2002-2004 by David Brownell
 * All Rights Reserved.
 *
 * This software is licensed under the GNU GPL version 2.
 */

#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 that are handled
 *	directly by DMA controllers.
 * @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, so this request and
 *	its buffer may be re-used.
 *	Reads terminate with a short packet, or when the buffer fills,
 *	whichever comes first.  When writes terminate, some data bytes
 *	will usually still be in flight (often in a hardware fifo).
 *	Errors (for reads or writes) stop the queue from advancing
 *	until the completion function returns, so that any transfers
 *	invalidated by the error may first be dequeued.
 * @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 bytes transferred to/from the buffer.  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) some data bytes may still
 * 	reside in a device-side FIFO when the request is reported as
 *	complete.
 *
 * 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.

struct usb_request {
	void			*buf;
	unsigned		length;
	dma_addr_t		dma;

	unsigned		no_interrupt:1;
	unsigned		zero:1;
	unsigned		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,
		gfp_t 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, gfp_t gfp_flags);
	void (*free_buffer) (struct usb_ep *ep, void *buf, dma_addr_t dma,
		unsigned bytes);
	// NOTE:  on 2.6, drivers may also use dma_map() and
	// dma_sync_single_*() to directly manage dma overhead. 

	int (*queue) (struct usb_ep *ep, struct usb_request *req,
		gfp_t 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"
 * @ops: Function pointers used to access hardware-specific operations.
 * @ep_list:the gadget's ep_list holds all of its endpoints
 * @maxpacket:The maximum packet size used on this endpoint.  The initial
 *	value can sometimes be reduced (hardware allowing), according to
 *      the endpoint descriptor used to configure the endpoint.
 * @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, gfp_t 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_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.
 * Drivers can rely on the fact that the first byte of the request's buffer
 * always corresponds to the first byte of some USB packet, for both
 * IN and OUT transfers.
 *
 * 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 (even 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.
 * (Note that some USB device controllers disallow protocol stall responses
 * in some cases.)  When control responses are deferred (the response is
 * written after the setup callback returns), then usb_ep_set_halt() may be
 * used on ep0 to trigger 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
 * 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, gfp_t 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.
 *
 * Note that while an endpoint CLEAR_FEATURE will be invisible to the
 * gadget driver, a SET_INTERFACE will not be.  To reset endpoints for the
 * current altsetting, see usb_ep_clear_halt().  When switching altsettings,
 * it's simplest to use usb_ep_enable() or usb_ep_disable() for the endpoints.
 *
 * Returns zero, or a negative error code.  On success, this call sets
 * underlying hardware state that blocks data transfers.
 * Attempts to halt IN endpoints will fail (returning -EAGAIN) if any
 * transfer requests are still queued, or if the controller hardware
 * (usually a FIFO) still holds bytes that the host hasn't collected.
 */
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.
 * Note that some hardware can't support this request (like pxa2xx_udc),
 * and accordingly can't correctly implement interface altsettings.
 */
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 (and 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 is_selfpowered);
	int	(*vbus_session) (struct usb_gadget *, int is_active);
	int	(*vbus_draw) (struct usb_gadget *, unsigned mA);
	int	(*pullup) (struct usb_gadget *, int is_on);
	int	(*ioctl)(struct usb_gadget *,
				unsigned code, unsigned long param);
};

/**
 * struct usb_gadget - represents a usb slave device
 * @ops: Function pointers used to access hardware-specific operations.
 * @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.
 * @is_dualspeed: True if the controller supports both high and full speed
 *	operation.  If it does, the gadget driver must also support both.
 * @is_otg: True if the USB device port uses a Mini-AB jack, so that the
 *	gadget driver must provide a USB OTG descriptor.
 * @is_a_peripheral: False unless is_otg, the "A" end of a USB cable
 *	is in the Mini-AB jack, and HNP has been used to switch roles
 *	so that the "A" device currently acts as A-Peripheral, not A-Host.
 * @a_hnp_support: OTG device feature flag, indicating that the A-Host
 *	supports HNP at this port.
 * @a_alt_hnp_support: OTG device feature flag, indicating that the A-Host
 *	only supports HNP on a different root port.
 * @b_hnp_enable: OTG device feature flag, indicating that the A-Host
 *	enabled HNP support.
 * @name: Identifies the controller hardware type.  Used in diagnostics
 * 	and sometimes configuration.
 * @dev: Driver model state for this abstract device.
 *
 * Gadgets have a mostly-portable "gadget driver" implementing device
 * functions, handling all usb configurations and interfaces.  Gadget
 * drivers talk to hardware-specific code indirectly, through ops vectors.
 * That insulates the gadget driver from hardware details, and packages
 * the hardware endpoints through generic i/o queues.  The "usb_gadget"
 * and "usb_ep" interfaces provide that insulation from the hardware.
 *
 * 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 2.6 (and later) kernels, and for
 * earlier systems is grouped in a similar structure that's not known
 * to the rest of the kernel.
 *
 * Values of the three OTG device feature flags are updated before the
 * setup() call corresponding to USB_REQ_SET_CONFIGURATION, and before
 * driver suspend() calls.  They are valid only when is_otg, and when the
 * device is acting as a B-Peripheral (so is_a_peripheral is false).
 */
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;
	unsigned			is_dualspeed:1;
	unsigned			is_otg:1;
	unsigned			is_a_peripheral:1;
	unsigned			b_hnp_enable:1;
	unsigned			a_hnp_support:1;
	unsigned			a_alt_hnp_support:1;
	const char			*name;
	struct device			dev;
};

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); }

/* 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)


/**
 * 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.
 *
 * This may also try to use SRP to wake the host and start enumeration,
 * even if OTG isn't otherwise in use.  OTG devices may also start
 * remote wakeup even when hosts don't explicitly 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);
}

/**
 * usb_gadget_vbus_connect - Notify controller that VBUS is powered
 * @gadget:The device which now has VBUS power.
 *
 * This call is used by a driver for an external transceiver (or GPIO)
 * that detects a VBUS power session starting.  Common responses include
 * resuming the controller, activating the D+ (or D-) pullup to let the
 * host detect that a USB device is attached, and starting to draw power
 * (8mA or possibly more, especially after SET_CONFIGURATION).
 *
 * Returns zero on success, else negative errno.
 */
static inline int
usb_gadget_vbus_connect(struct usb_gadget *gadget)
{
	if (!gadget->ops->vbus_session)
		return -EOPNOTSUPP;
	return gadget->ops->vbus_session (gadget, 1);
}

/**
 * usb_gadget_vbus_draw - constrain controller's VBUS power usage
 * @gadget:The device whose VBUS usage is being described
 * @mA:How much current to draw, in milliAmperes.  This should be twice
 *	the value listed in the configuration descriptor bMaxPower field.
 *
 * This call is used by gadget drivers during SET_CONFIGURATION calls,
 * reporting how much power the device may consume.  For example, this
 * could affect how quickly batteries are recharged.
 *
 * Returns zero on success, else negative errno.
 */
static inline int
usb_gadget_vbus_draw(struct usb_gadget *gadget, unsigned mA)
{
	if (!gadget->ops->vbus_draw)
		return -EOPNOTSUPP;
	return gadget->ops->vbus_draw (gadget, mA);
}

/**
 * usb_gadget_vbus_disconnect - notify controller about VBUS session end
 * @gadget:the device whose VBUS supply is being described
 *
 * This call is used by a driver for an external transceiver (or GPIO)
 * that detects a VBUS power session ending.  Common responses include
 * reversing everything done in usb_gadget_vbus_connect().
 *
 * Returns zero on success, else negative errno.
 */
static inline int
usb_gadget_vbus_disconnect(struct usb_gadget *gadget)
{
	if (!gadget->ops->vbus_session)
		return -EOPNOTSUPP;
	return gadget->ops->vbus_session (gadget, 0);
}

/**
 * usb_gadget_connect - software-controlled connect to USB host
 * @gadget:the peripheral being connected
 *
 * Enables the D+ (or potentially D-) pullup.  The host will start
 * enumerating this gadget when the pullup is active and a VBUS session
 * is active (the link is powered).  This pullup is always enabled unless
 * usb_gadget_disconnect() has been used to disable it.
 *
 * Returns zero on success, else negative errno.
 */
static inline int
usb_gadget_connect (struct usb_gadget *gadget)
{
	if (!gadget->ops->pullup)
		return -EOPNOTSUPP;
	return gadget->ops->pullup (gadget, 1);
}

/**
 * usb_gadget_disconnect - software-controlled disconnect from USB host
 * @gadget:the peripheral being disconnected
 *
 * Disables the D+ (or potentially D-) pullup, which the host may see
 * as a disconnect (when a VBUS session is active).  Not all systems
 * support software pullup controls.
 *
 * This routine may be used during the gadget driver bind() call to prevent
 * the peripheral from ever being visible to the USB host, unless later
 * usb_gadget_connect() is called.  For example, user mode components may
 * need to be activated before the system can talk to hosts.
 *
 * Returns zero on success, else negative errno.
 */
static inline int
usb_gadget_disconnect (struct usb_gadget *gadget)
{
	if (!gadget->ops->pullup)
		return -EOPNOTSUPP;
	return gadget->ops->pullup (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
 * 	USB byte 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.  Some devices can't detect disconnect, so this might
 *	not be called except as part of controller shutdown.
 * @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.
 * @driver: Driver model state for this driver.
 *
 * 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.
 *
 * If gadget->is_otg is true, the gadget driver must provide an OTG
 * descriptor during enumeration, or else fail the bind() call.  In such
 * cases, no USB traffic may flow until both bind() returns without
 * having called usb_gadget_disconnect(), and the USB host stack has
 * initialized.
 *
 * 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; or an error state might
 * be cleared, to make the device behave identically whether or not
 * power is maintained.
 */
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
	struct device_driver	driver;
};



/*-------------------------------------------------------------------------*/

/* 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 before this registration call returns.  It's expected that
 * the bind() functions will be in init sections.
 * 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.  It's expected that the unbind() functions
 * will in in exit sections, so may not be linked in some kernels.
 * 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 UTF-8 encoding
 *
 * 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);

/*-------------------------------------------------------------------------*/

/* utility to simplify managing config descriptors */

/* write vector of descriptors into buffer */
int usb_descriptor_fillbuf(void *, unsigned,
		const struct usb_descriptor_header **);

/* build config descriptor from single descriptor vector */
int usb_gadget_config_buf(const struct usb_config_descriptor *config,
	void *buf, unsigned buflen, const struct usb_descriptor_header **desc);

/*-------------------------------------------------------------------------*/

/* utility wrapping a simple endpoint selection policy */

extern struct usb_ep *usb_ep_autoconfig (struct usb_gadget *,
			struct usb_endpoint_descriptor *) __devinit;

extern void usb_ep_autoconfig_reset (struct usb_gadget *) __devinit;

#endif  /* __KERNEL__ */

#endif	/* __LINUX_USB_GADGET_H */