[PATCH] USB: USB API documentation modification

[linux-2.6/linux-loongson.git] / drivers / usb / core / urb.c

#include <linux/config.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/init.h>

#ifdef CONFIG_USB_DEBUG
        #define DEBUG
#else
        #undef DEBUG
#endif
#include <linux/usb.h>
#include "hcd.h"

#define to_urb(d) container_of(d, struct urb, kref)

static void urb_destroy(struct kref *kref)
{
        struct urb *urb = to_urb(kref);
        kfree(urb);
}

/**
 * usb_init_urb - initializes a urb so that it can be used by a USB driver
 * @urb: pointer to the urb to initialize
 *
 * Initializes a urb so that the USB subsystem can use it properly.
 *
 * If a urb is created with a call to usb_alloc_urb() it is not
 * necessary to call this function.  Only use this if you allocate the
 * space for a struct urb on your own.  If you call this function, be
 * careful when freeing the memory for your urb that it is no longer in
 * use by the USB core.
 *
 * Only use this function if you _really_ understand what you are doing.
 */
void usb_init_urb(struct urb *urb)
{
        if (urb) {
                memset(urb, 0, sizeof(*urb));
                kref_init(&urb->kref);
                spin_lock_init(&urb->lock);
        }
}

/**
 * usb_alloc_urb - creates a new urb for a USB driver to use
 * @iso_packets: number of iso packets for this urb
 * @mem_flags: the type of memory to allocate, see kmalloc() for a list of
 *      valid options for this.
 *
 * Creates an urb for the USB driver to use, initializes a few internal
 * structures, incrementes the usage counter, and returns a pointer to it.
 *
 * If no memory is available, NULL is returned.
 *
 * If the driver want to use this urb for interrupt, control, or bulk
 * endpoints, pass '0' as the number of iso packets.
 *
 * The driver must call usb_free_urb() when it is finished with the urb.
 */
struct urb *usb_alloc_urb(int iso_packets, int mem_flags)
{
        struct urb *urb;

        urb = (struct urb *)kmalloc(sizeof(struct urb) + 
                iso_packets * sizeof(struct usb_iso_packet_descriptor),
                mem_flags);
        if (!urb) {
                err("alloc_urb: kmalloc failed");
                return NULL;
        }
        usb_init_urb(urb);
        return urb;
}

/**
 * usb_free_urb - frees the memory used by a urb when all users of it are finished
 * @urb: pointer to the urb to free, may be NULL
 *
 * Must be called when a user of a urb is finished with it.  When the last user
 * of the urb calls this function, the memory of the urb is freed.
 *
 * Note: The transfer buffer associated with the urb is not freed, that must be
 * done elsewhere.
 */
void usb_free_urb(struct urb *urb)
{
        if (urb)
                kref_put(&urb->kref, urb_destroy);
}

/**
 * usb_get_urb - increments the reference count of the urb
 * @urb: pointer to the urb to modify, may be NULL
 *
 * This must be  called whenever a urb is transferred from a device driver to a
 * host controller driver.  This allows proper reference counting to happen
 * for urbs.
 *
 * A pointer to the urb with the incremented reference counter is returned.
 */
struct urb * usb_get_urb(struct urb *urb)
{
        if (urb)
                kref_get(&urb->kref);
        return urb;
}
                
                
/*-------------------------------------------------------------------*/

/**
 * usb_submit_urb - issue an asynchronous transfer request for an endpoint
 * @urb: pointer to the urb describing the request
 * @mem_flags: the type of memory to allocate, see kmalloc() for a list
 *      of valid options for this.
 *
 * This submits a transfer request, and transfers control of the URB
 * describing that request to the USB subsystem.  Request completion will
 * be indicated later, asynchronously, by calling the completion handler.
 * The three types of completion are success, error, and unlink
 * (a software-induced fault, also called "request cancelation").  
 *
 * URBs may be submitted in interrupt context.
 *
 * The caller must have correctly initialized the URB before submitting
 * it.  Functions such as usb_fill_bulk_urb() and usb_fill_control_urb() are
 * available to ensure that most fields are correctly initialized, for
 * the particular kind of transfer, although they will not initialize
 * any transfer flags.
 *
 * Successful submissions return 0; otherwise this routine returns a
 * negative error number.  If the submission is successful, the complete()
 * callback from the URB will be called exactly once, when the USB core and
 * Host Controller Driver (HCD) are finished with the URB.  When the completion
 * function is called, control of the URB is returned to the device
 * driver which issued the request.  The completion handler may then
 * immediately free or reuse that URB.
 *
 * With few exceptions, USB device drivers should never access URB fields
 * provided by usbcore or the HCD until its complete() is called.
 * The exceptions relate to periodic transfer scheduling.  For both
 * interrupt and isochronous urbs, as part of successful URB submission
 * urb->interval is modified to reflect the actual transfer period used
 * (normally some power of two units).  And for isochronous urbs,
 * urb->start_frame is modified to reflect when the URB's transfers were
 * scheduled to start.  Not all isochronous transfer scheduling policies
 * will work, but most host controller drivers should easily handle ISO
 * queues going from now until 10-200 msec into the future.
 *
 * For control endpoints, the synchronous usb_control_msg() call is
 * often used (in non-interrupt context) instead of this call.
 * That is often used through convenience wrappers, for the requests
 * that are standardized in the USB 2.0 specification.  For bulk
 * endpoints, a synchronous usb_bulk_msg() call is available.
 *
 * Request Queuing:
 *
 * URBs may be submitted to endpoints before previous ones complete, to
 * minimize the impact of interrupt latencies and system overhead on data
 * throughput.  With that queuing policy, an endpoint's queue would never
 * be empty.  This is required for continuous isochronous data streams,
 * and may also be required for some kinds of interrupt transfers. Such
 * queuing also maximizes bandwidth utilization by letting USB controllers
 * start work on later requests before driver software has finished the
 * completion processing for earlier (successful) requests.
 *
 * As of Linux 2.6, all USB endpoint transfer queues support depths greater
 * than one.  This was previously a HCD-specific behavior, except for ISO
 * transfers.  Non-isochronous endpoint queues are inactive during cleanup
 * after faults (transfer errors or cancelation).
 *
 * Reserved Bandwidth Transfers:
 *
 * Periodic transfers (interrupt or isochronous) are performed repeatedly,
 * using the interval specified in the urb.  Submitting the first urb to
 * the endpoint reserves the bandwidth necessary to make those transfers.
 * If the USB subsystem can't allocate sufficient bandwidth to perform
 * the periodic request, submitting such a periodic request should fail.
 *
 * Device drivers must explicitly request that repetition, by ensuring that
 * some URB is always on the endpoint's queue (except possibly for short
 * periods during completion callacks).  When there is no longer an urb
 * queued, the endpoint's bandwidth reservation is canceled.  This means
 * drivers can use their completion handlers to ensure they keep bandwidth
 * they need, by reinitializing and resubmitting the just-completed urb
 * until the driver longer needs that periodic bandwidth.
 *
 * Memory Flags:
 *
 * The general rules for how to decide which mem_flags to use
 * are the same as for kmalloc.  There are four
 * different possible values; GFP_KERNEL, GFP_NOFS, GFP_NOIO and
 * GFP_ATOMIC.
 *
 * GFP_NOFS is not ever used, as it has not been implemented yet.
 *
 * GFP_ATOMIC is used when
 *   (a) you are inside a completion handler, an interrupt, bottom half,
 *       tasklet or timer, or
 *   (b) you are holding a spinlock or rwlock (does not apply to
 *       semaphores), or
 *   (c) current->state != TASK_RUNNING, this is the case only after
 *       you've changed it.
 * 
 * GFP_NOIO is used in the block io path and error handling of storage
 * devices.
 *
 * All other situations use GFP_KERNEL.
 *
 * Some more specific rules for mem_flags can be inferred, such as
 *  (1) start_xmit, timeout, and receive methods of network drivers must
 *      use GFP_ATOMIC (they are called with a spinlock held);
 *  (2) queuecommand methods of scsi drivers must use GFP_ATOMIC (also
 *      called with a spinlock held);
 *  (3) If you use a kernel thread with a network driver you must use
 *      GFP_NOIO, unless (b) or (c) apply;
 *  (4) after you have done a down() you can use GFP_KERNEL, unless (b) or (c)
 *      apply or your are in a storage driver's block io path;
 *  (5) USB probe and disconnect can use GFP_KERNEL unless (b) or (c) apply; and
 *  (6) changing firmware on a running storage or net device uses
 *      GFP_NOIO, unless b) or c) apply
 *
 */
int usb_submit_urb(struct urb *urb, int mem_flags)
{
        int                     pipe, temp, max;
        struct usb_device       *dev;
        struct usb_operations   *op;
        int                     is_out;

        if (!urb || urb->hcpriv || !urb->complete)
                return -EINVAL;
        if (!(dev = urb->dev) ||
            (dev->state < USB_STATE_DEFAULT) ||
            (!dev->bus) || (dev->devnum <= 0))
                return -ENODEV;
        if (dev->state == USB_STATE_SUSPENDED)
                return -EHOSTUNREACH;
        if (!(op = dev->bus->op) || !op->submit_urb)
                return -ENODEV;

        urb->status = -EINPROGRESS;
        urb->actual_length = 0;
        urb->bandwidth = 0;

        /* Lots of sanity checks, so HCDs can rely on clean data
         * and don't need to duplicate tests
         */
        pipe = urb->pipe;
        temp = usb_pipetype (pipe);
        is_out = usb_pipeout (pipe);

        if (!usb_pipecontrol (pipe) && dev->state < USB_STATE_CONFIGURED)
                return -ENODEV;

        /* FIXME there should be a sharable lock protecting us against
         * config/altsetting changes and disconnects, kicking in here.
         * (here == before maxpacket, and eventually endpoint type,
         * checks get made.)
         */

        max = usb_maxpacket (dev, pipe, is_out);
        if (max <= 0) {
                dev_dbg(&dev->dev,
                        "bogus endpoint ep%d%s in %s (bad maxpacket %d)\n",
                        usb_pipeendpoint (pipe), is_out ? "out" : "in",
                        __FUNCTION__, max);
                return -EMSGSIZE;
        }

        /* periodic transfers limit size per frame/uframe,
         * but drivers only control those sizes for ISO.
         * while we're checking, initialize return status.
         */
        if (temp == PIPE_ISOCHRONOUS) {
                int     n, len;

                /* "high bandwidth" mode, 1-3 packets/uframe? */
                if (dev->speed == USB_SPEED_HIGH) {
                        int     mult = 1 + ((max >> 11) & 0x03);
                        max &= 0x07ff;
                        max *= mult;
                }

                if (urb->number_of_packets <= 0)                    
                        return -EINVAL;
                for (n = 0; n < urb->number_of_packets; n++) {
                        len = urb->iso_frame_desc [n].length;
                        if (len < 0 || len > max) 
                                return -EMSGSIZE;
                        urb->iso_frame_desc [n].status = -EXDEV;
                        urb->iso_frame_desc [n].actual_length = 0;
                }
        }

        /* the I/O buffer must be mapped/unmapped, except when length=0 */
        if (urb->transfer_buffer_length < 0)
                return -EMSGSIZE;

#ifdef DEBUG
        /* stuff that drivers shouldn't do, but which shouldn't
         * cause problems in HCDs if they get it wrong.
         */
        {
        unsigned int    orig_flags = urb->transfer_flags;
        unsigned int    allowed;

        /* enforce simple/standard policy */
        allowed = URB_ASYNC_UNLINK;     // affects later unlinks
        allowed |= (URB_NO_TRANSFER_DMA_MAP | URB_NO_SETUP_DMA_MAP);
        allowed |= URB_NO_INTERRUPT;
        switch (temp) {
        case PIPE_BULK:
                if (is_out)
                        allowed |= URB_ZERO_PACKET;
                /* FALLTHROUGH */
        case PIPE_CONTROL:
                allowed |= URB_NO_FSBR; /* only affects UHCI */
                /* FALLTHROUGH */
        default:                        /* all non-iso endpoints */
                if (!is_out)
                        allowed |= URB_SHORT_NOT_OK;
                break;
        case PIPE_ISOCHRONOUS:
                allowed |= URB_ISO_ASAP;
                break;
        }
        urb->transfer_flags &= allowed;

        /* fail if submitter gave bogus flags */
        if (urb->transfer_flags != orig_flags) {
                err ("BOGUS urb flags, %x --> %x",
                        orig_flags, urb->transfer_flags);
                return -EINVAL;
        }
        }
#endif
        /*
         * Force periodic transfer intervals to be legal values that are
         * a power of two (so HCDs don't need to).
         *
         * FIXME want bus->{intr,iso}_sched_horizon values here.  Each HC
         * supports different values... this uses EHCI/UHCI defaults (and
         * EHCI can use smaller non-default values).
         */
        switch (temp) {
        case PIPE_ISOCHRONOUS:
        case PIPE_INTERRUPT:
                /* too small? */
                if (urb->interval <= 0)
                        return -EINVAL;
                /* too big? */
                switch (dev->speed) {
                case USB_SPEED_HIGH:    /* units are microframes */
                        // NOTE usb handles 2^15
                        if (urb->interval > (1024 * 8))
                                urb->interval = 1024 * 8;
                        temp = 1024 * 8;
                        break;
                case USB_SPEED_FULL:    /* units are frames/msec */
                case USB_SPEED_LOW:
                        if (temp == PIPE_INTERRUPT) {
                                if (urb->interval > 255)
                                        return -EINVAL;
                                // NOTE ohci only handles up to 32
                                temp = 128;
                        } else {
                                if (urb->interval > 1024)
                                        urb->interval = 1024;
                                // NOTE usb and ohci handle up to 2^15
                                temp = 1024;
                        }
                        break;
                default:
                        return -EINVAL;
                }
                /* power of two? */
                while (temp > urb->interval)
                        temp >>= 1;
                urb->interval = temp;
        }

        return op->submit_urb (urb, mem_flags);
}

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

/**
 * usb_unlink_urb - abort/cancel a transfer request for an endpoint
 * @urb: pointer to urb describing a previously submitted request,
 *      may be NULL
 *
 * This routine cancels an in-progress request.  URBs complete only
 * once per submission, and may be canceled only once per submission.
 * Successful cancelation means the requests's completion handler will
 * be called with a status code indicating that the request has been
 * canceled (rather than any other code) and will quickly be removed
 * from host controller data structures.
 *
 * In the past, clearing the URB_ASYNC_UNLINK transfer flag for the
 * URB indicated that the request was synchronous.  This usage is now
 * deprecated; if the flag is clear the call will be forwarded to
 * usb_kill_urb() and the return value will be 0.  In the future, drivers
 * should call usb_kill_urb() directly for synchronous unlinking.
 *
 * When the URB_ASYNC_UNLINK transfer flag for the URB is set, this
 * request is asynchronous.  Success is indicated by returning -EINPROGRESS,
 * at which time the URB will normally have been unlinked but not yet
 * given back to the device driver.  When it is called, the completion
 * function will see urb->status == -ECONNRESET.  Failure is indicated
 * by any other return value.  Unlinking will fail when the URB is not
 * currently "linked" (i.e., it was never submitted, or it was unlinked
 * before, or the hardware is already finished with it), even if the
 * completion handler has not yet run.
 *
 * Unlinking and Endpoint Queues:
 *
 * Host Controller Drivers (HCDs) place all the URBs for a particular
 * endpoint in a queue.  Normally the queue advances as the controller
 * hardware processes each request.  But when an URB terminates with an
 * error its queue stops, at least until that URB's completion routine
 * returns.  It is guaranteed that the queue will not restart until all
 * its unlinked URBs have been fully retired, with their completion
 * routines run, even if that's not until some time after the original
 * completion handler returns.  Normally the same behavior and guarantees
 * apply when an URB terminates because it was unlinked; however if an
 * URB is unlinked before the hardware has started to execute it, then
 * its queue is not guaranteed to stop until all the preceding URBs have
 * completed.
 *
 * This means that USB device drivers can safely build deep queues for
 * large or complex transfers, and clean them up reliably after any sort
 * of aborted transfer by unlinking all pending URBs at the first fault.
 *
 * Note that an URB terminating early because a short packet was received
 * will count as an error if and only if the URB_SHORT_NOT_OK flag is set.
 * Also, that all unlinks performed in any URB completion handler must
 * be asynchronous.
 *
 * Queues for isochronous endpoints are treated differently, because they
 * advance at fixed rates.  Such queues do not stop when an URB is unlinked.
 * An unlinked URB may leave a gap in the stream of packets.  It is undefined
 * whether such gaps can be filled in.
 *
 * When a control URB terminates with an error, it is likely that the
 * status stage of the transfer will not take place, even if it is merely
 * a soft error resulting from a short-packet with URB_SHORT_NOT_OK set.
 */
int usb_unlink_urb(struct urb *urb)
{
        if (!urb)
                return -EINVAL;
        if (!(urb->transfer_flags & URB_ASYNC_UNLINK)) {
#ifdef CONFIG_DEBUG_KERNEL
                if (printk_ratelimit()) {
                        printk(KERN_NOTICE "usb_unlink_urb() is deprecated for "
                                "synchronous unlinks.  Use usb_kill_urb() instead.\n");
                        WARN_ON(1);
                }
#endif
                usb_kill_urb(urb);
                return 0;
        }
        if (!(urb->dev && urb->dev->bus && urb->dev->bus->op))
                return -ENODEV;
        return urb->dev->bus->op->unlink_urb(urb, -ECONNRESET);
}

/**
 * usb_kill_urb - cancel a transfer request and wait for it to finish
 * @urb: pointer to URB describing a previously submitted request,
 *      may be NULL
 *
 * This routine cancels an in-progress request.  It is guaranteed that
 * upon return all completion handlers will have finished and the URB
 * will be totally idle and available for reuse.  These features make
 * this an ideal way to stop I/O in a disconnect() callback or close()
 * function.  If the request has not already finished or been unlinked
 * the completion handler will see urb->status == -ENOENT.
 *
 * While the routine is running, attempts to resubmit the URB will fail
 * with error -EPERM.  Thus even if the URB's completion handler always
 * tries to resubmit, it will not succeed and the URB will become idle.
 *
 * This routine may not be used in an interrupt context (such as a bottom
 * half or a completion handler), or when holding a spinlock, or in other
 * situations where the caller can't schedule().
 */
void usb_kill_urb(struct urb *urb)
{
        if (!(urb && urb->dev && urb->dev->bus && urb->dev->bus->op))
                return;
        spin_lock_irq(&urb->lock);
        ++urb->reject;
        spin_unlock_irq(&urb->lock);

        urb->dev->bus->op->unlink_urb(urb, -ENOENT);
        wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);

        spin_lock_irq(&urb->lock);
        --urb->reject;
        spin_unlock_irq(&urb->lock);
}

EXPORT_SYMBOL(usb_init_urb);
EXPORT_SYMBOL(usb_alloc_urb);
EXPORT_SYMBOL(usb_free_urb);
EXPORT_SYMBOL(usb_get_urb);
EXPORT_SYMBOL(usb_submit_urb);
EXPORT_SYMBOL(usb_unlink_urb);
EXPORT_SYMBOL(usb_kill_urb);