[PATCH] s390: fix in-user atomic futex operation.

[linux/fpc-iii.git] / drivers / parport / share.c

/* $Id: parport_share.c,v 1.15 1998/01/11 12:06:17 philip Exp $
 * Parallel-port resource manager code.
 * 
 * Authors: David Campbell <campbell@tirian.che.curtin.edu.au>
 *          Tim Waugh <tim@cyberelk.demon.co.uk>
 *          Jose Renau <renau@acm.org>
 *          Philip Blundell <philb@gnu.org>
 *          Andrea Arcangeli
 *
 * based on work by Grant Guenther <grant@torque.net>
 *          and Philip Blundell
 *
 * Any part of this program may be used in documents licensed under
 * the GNU Free Documentation License, Version 1.1 or any later version
 * published by the Free Software Foundation.
 */

#undef PARPORT_DEBUG_SHARING            /* undef for production */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/threads.h>
#include <linux/parport.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/kmod.h>

#include <linux/spinlock.h>
#include <linux/mutex.h>
#include <asm/irq.h>

#undef PARPORT_PARANOID

#define PARPORT_DEFAULT_TIMESLICE       (HZ/5)

unsigned long parport_default_timeslice = PARPORT_DEFAULT_TIMESLICE;
int parport_default_spintime =  DEFAULT_SPIN_TIME;

static LIST_HEAD(portlist);
static DEFINE_SPINLOCK(parportlist_lock);

/* list of all allocated ports, sorted by ->number */
static LIST_HEAD(all_ports);
static DEFINE_SPINLOCK(full_list_lock);

static LIST_HEAD(drivers);

static DEFINE_MUTEX(registration_lock);

/* What you can do to a port that's gone away.. */
static void dead_write_lines (struct parport *p, unsigned char b){}
static unsigned char dead_read_lines (struct parport *p) { return 0; }
static unsigned char dead_frob_lines (struct parport *p, unsigned char b,
                             unsigned char c) { return 0; }
static void dead_onearg (struct parport *p){}
static void dead_initstate (struct pardevice *d, struct parport_state *s) { }
static void dead_state (struct parport *p, struct parport_state *s) { }
static size_t dead_write (struct parport *p, const void *b, size_t l, int f)
{ return 0; }
static size_t dead_read (struct parport *p, void *b, size_t l, int f)
{ return 0; }
static struct parport_operations dead_ops = {
        .write_data     = dead_write_lines,     /* data */
        .read_data      = dead_read_lines,

        .write_control  = dead_write_lines,     /* control */
        .read_control   = dead_read_lines,
        .frob_control   = dead_frob_lines,

        .read_status    = dead_read_lines,      /* status */

        .enable_irq     = dead_onearg,          /* enable_irq */
        .disable_irq    = dead_onearg,          /* disable_irq */

        .data_forward   = dead_onearg,          /* data_forward */
        .data_reverse   = dead_onearg,          /* data_reverse */

        .init_state     = dead_initstate,       /* init_state */
        .save_state     = dead_state,
        .restore_state  = dead_state,

        .epp_write_data = dead_write,           /* epp */
        .epp_read_data  = dead_read,
        .epp_write_addr = dead_write,
        .epp_read_addr  = dead_read,

        .ecp_write_data = dead_write,           /* ecp */
        .ecp_read_data  = dead_read,
        .ecp_write_addr = dead_write,
 
        .compat_write_data      = dead_write,   /* compat */
        .nibble_read_data       = dead_read,    /* nibble */
        .byte_read_data         = dead_read,    /* byte */

        .owner          = NULL,
};

/* Call attach(port) for each registered driver. */
static void attach_driver_chain(struct parport *port)
{
        /* caller has exclusive registration_lock */
        struct parport_driver *drv;
        list_for_each_entry(drv, &drivers, list)
                drv->attach(port);
}

/* Call detach(port) for each registered driver. */
static void detach_driver_chain(struct parport *port)
{
        struct parport_driver *drv;
        /* caller has exclusive registration_lock */
        list_for_each_entry(drv, &drivers, list)
                drv->detach (port);
}

/* Ask kmod for some lowlevel drivers. */
static void get_lowlevel_driver (void)
{
        /* There is no actual module called this: you should set
         * up an alias for modutils. */
        request_module ("parport_lowlevel");
}

/**
 *      parport_register_driver - register a parallel port device driver
 *      @drv: structure describing the driver
 *
 *      This can be called by a parallel port device driver in order
 *      to receive notifications about ports being found in the
 *      system, as well as ports no longer available.
 *
 *      The @drv structure is allocated by the caller and must not be
 *      deallocated until after calling parport_unregister_driver().
 *
 *      The driver's attach() function may block.  The port that
 *      attach() is given will be valid for the duration of the
 *      callback, but if the driver wants to take a copy of the
 *      pointer it must call parport_get_port() to do so.  Calling
 *      parport_register_device() on that port will do this for you.
 *
 *      The driver's detach() function may block.  The port that
 *      detach() is given will be valid for the duration of the
 *      callback, but if the driver wants to take a copy of the
 *      pointer it must call parport_get_port() to do so.
 *
 *      Returns 0 on success.  Currently it always succeeds.
 **/

int parport_register_driver (struct parport_driver *drv)
{
        struct parport *port;

        if (list_empty(&portlist))
                get_lowlevel_driver ();

        mutex_lock(&registration_lock);
        list_for_each_entry(port, &portlist, list)
                drv->attach(port);
        list_add(&drv->list, &drivers);
        mutex_unlock(&registration_lock);

        return 0;
}

/**
 *      parport_unregister_driver - deregister a parallel port device driver
 *      @drv: structure describing the driver that was given to
 *            parport_register_driver()
 *
 *      This should be called by a parallel port device driver that
 *      has registered itself using parport_register_driver() when it
 *      is about to be unloaded.
 *
 *      When it returns, the driver's attach() routine will no longer
 *      be called, and for each port that attach() was called for, the
 *      detach() routine will have been called.
 *
 *      All the driver's attach() and detach() calls are guaranteed to have
 *      finished by the time this function returns.
 **/

void parport_unregister_driver (struct parport_driver *drv)
{
        struct parport *port;

        mutex_lock(&registration_lock);
        list_del_init(&drv->list);
        list_for_each_entry(port, &portlist, list)
                drv->detach(port);
        mutex_unlock(&registration_lock);
}

static void free_port (struct parport *port)
{
        int d;
        spin_lock(&full_list_lock);
        list_del(&port->full_list);
        spin_unlock(&full_list_lock);
        for (d = 0; d < 5; d++) {
                kfree(port->probe_info[d].class_name);
                kfree(port->probe_info[d].mfr);
                kfree(port->probe_info[d].model);
                kfree(port->probe_info[d].cmdset);
                kfree(port->probe_info[d].description);
        }

        kfree(port->name);
        kfree(port);
}

/**
 *      parport_get_port - increment a port's reference count
 *      @port: the port
 *
 *      This ensure's that a struct parport pointer remains valid
 *      until the matching parport_put_port() call.
 **/

struct parport *parport_get_port (struct parport *port)
{
        atomic_inc (&port->ref_count);
        return port;
}

/**
 *      parport_put_port - decrement a port's reference count
 *      @port: the port
 *
 *      This should be called once for each call to parport_get_port(),
 *      once the port is no longer needed.
 **/

void parport_put_port (struct parport *port)
{
        if (atomic_dec_and_test (&port->ref_count))
                /* Can destroy it now. */
                free_port (port);

        return;
}

/**
 *      parport_register_port - register a parallel port
 *      @base: base I/O address
 *      @irq: IRQ line
 *      @dma: DMA channel
 *      @ops: pointer to the port driver's port operations structure
 *
 *      When a parallel port (lowlevel) driver finds a port that
 *      should be made available to parallel port device drivers, it
 *      should call parport_register_port().  The @base, @irq, and
 *      @dma parameters are for the convenience of port drivers, and
 *      for ports where they aren't meaningful needn't be set to
 *      anything special.  They can be altered afterwards by adjusting
 *      the relevant members of the parport structure that is returned
 *      and represents the port.  They should not be tampered with
 *      after calling parport_announce_port, however.
 *
 *      If there are parallel port device drivers in the system that
 *      have registered themselves using parport_register_driver(),
 *      they are not told about the port at this time; that is done by
 *      parport_announce_port().
 *
 *      The @ops structure is allocated by the caller, and must not be
 *      deallocated before calling parport_remove_port().
 *
 *      If there is no memory to allocate a new parport structure,
 *      this function will return %NULL.
 **/

struct parport *parport_register_port(unsigned long base, int irq, int dma,
                                      struct parport_operations *ops)
{
        struct list_head *l;
        struct parport *tmp;
        int num;
        int device;
        char *name;

        tmp = kmalloc(sizeof(struct parport), GFP_KERNEL);
        if (!tmp) {
                printk(KERN_WARNING "parport: memory squeeze\n");
                return NULL;
        }

        /* Init our structure */
        memset(tmp, 0, sizeof(struct parport));
        tmp->base = base;
        tmp->irq = irq;
        tmp->dma = dma;
        tmp->muxport = tmp->daisy = tmp->muxsel = -1;
        tmp->modes = 0;
        INIT_LIST_HEAD(&tmp->list);
        tmp->devices = tmp->cad = NULL;
        tmp->flags = 0;
        tmp->ops = ops;
        tmp->physport = tmp;
        memset (tmp->probe_info, 0, 5 * sizeof (struct parport_device_info));
        rwlock_init(&tmp->cad_lock);
        spin_lock_init(&tmp->waitlist_lock);
        spin_lock_init(&tmp->pardevice_lock);
        tmp->ieee1284.mode = IEEE1284_MODE_COMPAT;
        tmp->ieee1284.phase = IEEE1284_PH_FWD_IDLE;
        init_MUTEX_LOCKED (&tmp->ieee1284.irq); /* actually a semaphore at 0 */
        tmp->spintime = parport_default_spintime;
        atomic_set (&tmp->ref_count, 1);
        INIT_LIST_HEAD(&tmp->full_list);

        name = kmalloc(15, GFP_KERNEL);
        if (!name) {
                printk(KERN_ERR "parport: memory squeeze\n");
                kfree(tmp);
                return NULL;
        }
        /* Search for the lowest free parport number. */

        spin_lock(&full_list_lock);
        for (l = all_ports.next, num = 0; l != &all_ports; l = l->next, num++) {
                struct parport *p = list_entry(l, struct parport, full_list);
                if (p->number != num)
                        break;
        }
        tmp->portnum = tmp->number = num;
        list_add_tail(&tmp->full_list, l);
        spin_unlock(&full_list_lock);

        /*
         * Now that the portnum is known finish doing the Init.
         */
        sprintf(name, "parport%d", tmp->portnum = tmp->number);
        tmp->name = name;

        for (device = 0; device < 5; device++)
                /* assume the worst */
                tmp->probe_info[device].class = PARPORT_CLASS_LEGACY;

        tmp->waithead = tmp->waittail = NULL;

        return tmp;
}

/**
 *      parport_announce_port - tell device drivers about a parallel port
 *      @port: parallel port to announce
 *
 *      After a port driver has registered a parallel port with
 *      parport_register_port, and performed any necessary
 *      initialisation or adjustments, it should call
 *      parport_announce_port() in order to notify all device drivers
 *      that have called parport_register_driver().  Their attach()
 *      functions will be called, with @port as the parameter.
 **/

void parport_announce_port (struct parport *port)
{
        int i;

#ifdef CONFIG_PARPORT_1284
        /* Analyse the IEEE1284.3 topology of the port. */
        parport_daisy_init(port);
#endif

        parport_proc_register(port);
        mutex_lock(&registration_lock);
        spin_lock_irq(&parportlist_lock);
        list_add_tail(&port->list, &portlist);
        for (i = 1; i < 3; i++) {
                struct parport *slave = port->slaves[i-1];
                if (slave)
                        list_add_tail(&slave->list, &portlist);
        }
        spin_unlock_irq(&parportlist_lock);

        /* Let drivers know that new port(s) has arrived. */
        attach_driver_chain (port);
        for (i = 1; i < 3; i++) {
                struct parport *slave = port->slaves[i-1];
                if (slave)
                        attach_driver_chain(slave);
        }
        mutex_unlock(&registration_lock);
}

/**
 *      parport_remove_port - deregister a parallel port
 *      @port: parallel port to deregister
 *
 *      When a parallel port driver is forcibly unloaded, or a
 *      parallel port becomes inaccessible, the port driver must call
 *      this function in order to deal with device drivers that still
 *      want to use it.
 *
 *      The parport structure associated with the port has its
 *      operations structure replaced with one containing 'null'
 *      operations that return errors or just don't do anything.
 *
 *      Any drivers that have registered themselves using
 *      parport_register_driver() are notified that the port is no
 *      longer accessible by having their detach() routines called
 *      with @port as the parameter.
 **/

void parport_remove_port(struct parport *port)
{
        int i;

        mutex_lock(&registration_lock);

        /* Spread the word. */
        detach_driver_chain (port);

#ifdef CONFIG_PARPORT_1284
        /* Forget the IEEE1284.3 topology of the port. */
        parport_daisy_fini(port);
        for (i = 1; i < 3; i++) {
                struct parport *slave = port->slaves[i-1];
                if (!slave)
                        continue;
                detach_driver_chain(slave);
                parport_daisy_fini(slave);
        }
#endif

        port->ops = &dead_ops;
        spin_lock(&parportlist_lock);
        list_del_init(&port->list);
        for (i = 1; i < 3; i++) {
                struct parport *slave = port->slaves[i-1];
                if (slave)
                        list_del_init(&slave->list);
        }
        spin_unlock(&parportlist_lock);

        mutex_unlock(&registration_lock);

        parport_proc_unregister(port);

        for (i = 1; i < 3; i++) {
                struct parport *slave = port->slaves[i-1];
                if (slave)
                        parport_put_port(slave);
        }
}

/**
 *      parport_register_device - register a device on a parallel port
 *      @port: port to which the device is attached
 *      @name: a name to refer to the device
 *      @pf: preemption callback
 *      @kf: kick callback (wake-up)
 *      @irq_func: interrupt handler
 *      @flags: registration flags
 *      @handle: data for callback functions
 *
 *      This function, called by parallel port device drivers,
 *      declares that a device is connected to a port, and tells the
 *      system all it needs to know.
 *
 *      The @name is allocated by the caller and must not be
 *      deallocated until the caller calls @parport_unregister_device
 *      for that device.
 *
 *      The preemption callback function, @pf, is called when this
 *      device driver has claimed access to the port but another
 *      device driver wants to use it.  It is given @handle as its
 *      parameter, and should return zero if it is willing for the
 *      system to release the port to another driver on its behalf.
 *      If it wants to keep control of the port it should return
 *      non-zero, and no action will be taken.  It is good manners for
 *      the driver to try to release the port at the earliest
 *      opportunity after its preemption callback rejects a preemption
 *      attempt.  Note that if a preemption callback is happy for
 *      preemption to go ahead, there is no need to release the port;
 *      it is done automatically.  This function may not block, as it
 *      may be called from interrupt context.  If the device driver
 *      does not support preemption, @pf can be %NULL.
 *
 *      The wake-up ("kick") callback function, @kf, is called when
 *      the port is available to be claimed for exclusive access; that
 *      is, parport_claim() is guaranteed to succeed when called from
 *      inside the wake-up callback function.  If the driver wants to
 *      claim the port it should do so; otherwise, it need not take
 *      any action.  This function may not block, as it may be called
 *      from interrupt context.  If the device driver does not want to
 *      be explicitly invited to claim the port in this way, @kf can
 *      be %NULL.
 *
 *      The interrupt handler, @irq_func, is called when an interrupt
 *      arrives from the parallel port.  Note that if a device driver
 *      wants to use interrupts it should use parport_enable_irq(),
 *      and can also check the irq member of the parport structure
 *      representing the port.
 *
 *      The parallel port (lowlevel) driver is the one that has called
 *      request_irq() and whose interrupt handler is called first.
 *      This handler does whatever needs to be done to the hardware to
 *      acknowledge the interrupt (for PC-style ports there is nothing
 *      special to be done).  It then tells the IEEE 1284 code about
 *      the interrupt, which may involve reacting to an IEEE 1284
 *      event depending on the current IEEE 1284 phase.  After this,
 *      it calls @irq_func.  Needless to say, @irq_func will be called
 *      from interrupt context, and may not block.
 *
 *      The %PARPORT_DEV_EXCL flag is for preventing port sharing, and
 *      so should only be used when sharing the port with other device
 *      drivers is impossible and would lead to incorrect behaviour.
 *      Use it sparingly!  Normally, @flags will be zero.
 *
 *      This function returns a pointer to a structure that represents
 *      the device on the port, or %NULL if there is not enough memory
 *      to allocate space for that structure.
 **/

struct pardevice *
parport_register_device(struct parport *port, const char *name,
                        int (*pf)(void *), void (*kf)(void *),
                        void (*irq_func)(int, void *, struct pt_regs *), 
                        int flags, void *handle)
{
        struct pardevice *tmp;

        if (port->physport->flags & PARPORT_FLAG_EXCL) {
                /* An exclusive device is registered. */
                printk (KERN_DEBUG "%s: no more devices allowed\n",
                        port->name);
                return NULL;
        }

        if (flags & PARPORT_DEV_LURK) {
                if (!pf || !kf) {
                        printk(KERN_INFO "%s: refused to register lurking device (%s) without callbacks\n", port->name, name);
                        return NULL;
                }
        }

        /* We up our own module reference count, and that of the port
           on which a device is to be registered, to ensure that
           neither of us gets unloaded while we sleep in (e.g.)
           kmalloc.
         */
        if (!try_module_get(port->ops->owner)) {
                return NULL;
        }
                
        parport_get_port (port);

        tmp = kmalloc(sizeof(struct pardevice), GFP_KERNEL);
        if (tmp == NULL) {
                printk(KERN_WARNING "%s: memory squeeze, couldn't register %s.\n", port->name, name);
                goto out;
        }

        tmp->state = kmalloc(sizeof(struct parport_state), GFP_KERNEL);
        if (tmp->state == NULL) {
                printk(KERN_WARNING "%s: memory squeeze, couldn't register %s.\n", port->name, name);
                goto out_free_pardevice;
        }

        tmp->name = name;
        tmp->port = port;
        tmp->daisy = -1;
        tmp->preempt = pf;
        tmp->wakeup = kf;
        tmp->private = handle;
        tmp->flags = flags;
        tmp->irq_func = irq_func;
        tmp->waiting = 0;
        tmp->timeout = 5 * HZ;

        /* Chain this onto the list */
        tmp->prev = NULL;
        /*
         * This function must not run from an irq handler so we don' t need
         * to clear irq on the local CPU. -arca
         */
        spin_lock(&port->physport->pardevice_lock);

        if (flags & PARPORT_DEV_EXCL) {
                if (port->physport->devices) {
                        spin_unlock (&port->physport->pardevice_lock);
                        printk (KERN_DEBUG
                                "%s: cannot grant exclusive access for "
                                "device %s\n", port->name, name);
                        goto out_free_all;
                }
                port->flags |= PARPORT_FLAG_EXCL;
        }

        tmp->next = port->physport->devices;
        wmb(); /* Make sure that tmp->next is written before it's
                  added to the list; see comments marked 'no locking
                  required' */
        if (port->physport->devices)
                port->physport->devices->prev = tmp;
        port->physport->devices = tmp;
        spin_unlock(&port->physport->pardevice_lock);

        init_waitqueue_head(&tmp->wait_q);
        tmp->timeslice = parport_default_timeslice;
        tmp->waitnext = tmp->waitprev = NULL;

        /*
         * This has to be run as last thing since init_state may need other
         * pardevice fields. -arca
         */
        port->ops->init_state(tmp, tmp->state);
        parport_device_proc_register(tmp);
        return tmp;

 out_free_all:
        kfree(tmp->state);
 out_free_pardevice:
        kfree(tmp);
 out:
        parport_put_port (port);
        module_put(port->ops->owner);

        return NULL;
}

/**
 *      parport_unregister_device - deregister a device on a parallel port
 *      @dev: pointer to structure representing device
 *
 *      This undoes the effect of parport_register_device().
 **/

void parport_unregister_device(struct pardevice *dev)
{
        struct parport *port;

#ifdef PARPORT_PARANOID
        if (dev == NULL) {
                printk(KERN_ERR "parport_unregister_device: passed NULL\n");
                return;
        }
#endif

        parport_device_proc_unregister(dev);

        port = dev->port->physport;

        if (port->cad == dev) {
                printk(KERN_DEBUG "%s: %s forgot to release port\n",
                       port->name, dev->name);
                parport_release (dev);
        }

        spin_lock(&port->pardevice_lock);
        if (dev->next)
                dev->next->prev = dev->prev;
        if (dev->prev)
                dev->prev->next = dev->next;
        else
                port->devices = dev->next;

        if (dev->flags & PARPORT_DEV_EXCL)
                port->flags &= ~PARPORT_FLAG_EXCL;

        spin_unlock(&port->pardevice_lock);

        /* Make sure we haven't left any pointers around in the wait
         * list. */
        spin_lock (&port->waitlist_lock);
        if (dev->waitprev || dev->waitnext || port->waithead == dev) {
                if (dev->waitprev)
                        dev->waitprev->waitnext = dev->waitnext;
                else
                        port->waithead = dev->waitnext;
                if (dev->waitnext)
                        dev->waitnext->waitprev = dev->waitprev;
                else
                        port->waittail = dev->waitprev;
        }
        spin_unlock (&port->waitlist_lock);

        kfree(dev->state);
        kfree(dev);

        module_put(port->ops->owner);
        parport_put_port (port);
}

/**
 *      parport_find_number - find a parallel port by number
 *      @number: parallel port number
 *
 *      This returns the parallel port with the specified number, or
 *      %NULL if there is none.
 *
 *      There is an implicit parport_get_port() done already; to throw
 *      away the reference to the port that parport_find_number()
 *      gives you, use parport_put_port().
 */

struct parport *parport_find_number (int number)
{
        struct parport *port, *result = NULL;

        if (list_empty(&portlist))
                get_lowlevel_driver ();

        spin_lock (&parportlist_lock);
        list_for_each_entry(port, &portlist, list) {
                if (port->number == number) {
                        result = parport_get_port (port);
                        break;
                }
        }
        spin_unlock (&parportlist_lock);
        return result;
}

/**
 *      parport_find_base - find a parallel port by base address
 *      @base: base I/O address
 *
 *      This returns the parallel port with the specified base
 *      address, or %NULL if there is none.
 *
 *      There is an implicit parport_get_port() done already; to throw
 *      away the reference to the port that parport_find_base()
 *      gives you, use parport_put_port().
 */

struct parport *parport_find_base (unsigned long base)
{
        struct parport *port, *result = NULL;

        if (list_empty(&portlist))
                get_lowlevel_driver ();

        spin_lock (&parportlist_lock);
        list_for_each_entry(port, &portlist, list) {
                if (port->base == base) {
                        result = parport_get_port (port);
                        break;
                }
        }
        spin_unlock (&parportlist_lock);
        return result;
}

/**
 *      parport_claim - claim access to a parallel port device
 *      @dev: pointer to structure representing a device on the port
 *
 *      This function will not block and so can be used from interrupt
 *      context.  If parport_claim() succeeds in claiming access to
 *      the port it returns zero and the port is available to use.  It
 *      may fail (returning non-zero) if the port is in use by another
 *      driver and that driver is not willing to relinquish control of
 *      the port.
 **/

int parport_claim(struct pardevice *dev)
{
        struct pardevice *oldcad;
        struct parport *port = dev->port->physport;
        unsigned long flags;

        if (port->cad == dev) {
                printk(KERN_INFO "%s: %s already owner\n",
                       dev->port->name,dev->name);
                return 0;
        }

        /* Preempt any current device */
        write_lock_irqsave (&port->cad_lock, flags);
        if ((oldcad = port->cad) != NULL) {
                if (oldcad->preempt) {
                        if (oldcad->preempt(oldcad->private))
                                goto blocked;
                        port->ops->save_state(port, dev->state);
                } else
                        goto blocked;

                if (port->cad != oldcad) {
                        /* I think we'll actually deadlock rather than
                           get here, but just in case.. */
                        printk(KERN_WARNING
                               "%s: %s released port when preempted!\n",
                               port->name, oldcad->name);
                        if (port->cad)
                                goto blocked;
                }
        }

        /* Can't fail from now on, so mark ourselves as no longer waiting.  */
        if (dev->waiting & 1) {
                dev->waiting = 0;

                /* Take ourselves out of the wait list again.  */
                spin_lock_irq (&port->waitlist_lock);
                if (dev->waitprev)
                        dev->waitprev->waitnext = dev->waitnext;
                else
                        port->waithead = dev->waitnext;
                if (dev->waitnext)
                        dev->waitnext->waitprev = dev->waitprev;
                else
                        port->waittail = dev->waitprev;
                spin_unlock_irq (&port->waitlist_lock);
                dev->waitprev = dev->waitnext = NULL;
        }

        /* Now we do the change of devices */
        port->cad = dev;

#ifdef CONFIG_PARPORT_1284
        /* If it's a mux port, select it. */
        if (dev->port->muxport >= 0) {
                /* FIXME */
                port->muxsel = dev->port->muxport;
        }

        /* If it's a daisy chain device, select it. */
        if (dev->daisy >= 0) {
                /* This could be lazier. */
                if (!parport_daisy_select (port, dev->daisy,
                                           IEEE1284_MODE_COMPAT))
                        port->daisy = dev->daisy;
        }
#endif /* IEEE1284.3 support */

        /* Restore control registers */
        port->ops->restore_state(port, dev->state);
        write_unlock_irqrestore(&port->cad_lock, flags);
        dev->time = jiffies;
        return 0;

blocked:
        /* If this is the first time we tried to claim the port, register an
           interest.  This is only allowed for devices sleeping in
           parport_claim_or_block(), or those with a wakeup function.  */

        /* The cad_lock is still held for writing here */
        if (dev->waiting & 2 || dev->wakeup) {
                spin_lock (&port->waitlist_lock);
                if (test_and_set_bit(0, &dev->waiting) == 0) {
                        /* First add ourselves to the end of the wait list. */
                        dev->waitnext = NULL;
                        dev->waitprev = port->waittail;
                        if (port->waittail) {
                                port->waittail->waitnext = dev;
                                port->waittail = dev;
                        } else
                                port->waithead = port->waittail = dev;
                }
                spin_unlock (&port->waitlist_lock);
        }
        write_unlock_irqrestore (&port->cad_lock, flags);
        return -EAGAIN;
}

/**
 *      parport_claim_or_block - claim access to a parallel port device
 *      @dev: pointer to structure representing a device on the port
 *
 *      This behaves like parport_claim(), but will block if necessary
 *      to wait for the port to be free.  A return value of 1
 *      indicates that it slept; 0 means that it succeeded without
 *      needing to sleep.  A negative error code indicates failure.
 **/

int parport_claim_or_block(struct pardevice *dev)
{
        int r;

        /* Signal to parport_claim() that we can wait even without a
           wakeup function.  */
        dev->waiting = 2;

        /* Try to claim the port.  If this fails, we need to sleep.  */
        r = parport_claim(dev);
        if (r == -EAGAIN) {
#ifdef PARPORT_DEBUG_SHARING
                printk(KERN_DEBUG "%s: parport_claim() returned -EAGAIN\n", dev->name);
#endif
                /*
                 * FIXME!!! Use the proper locking for dev->waiting,
                 * and make this use the "wait_event_interruptible()"
                 * interfaces. The cli/sti that used to be here
                 * did nothing.
                 *
                 * See also parport_release()
                 */

                /* If dev->waiting is clear now, an interrupt
                   gave us the port and we would deadlock if we slept.  */
                if (dev->waiting) {
                        interruptible_sleep_on (&dev->wait_q);
                        if (signal_pending (current)) {
                                return -EINTR;
                        }
                        r = 1;
                } else {
                        r = 0;
#ifdef PARPORT_DEBUG_SHARING
                        printk(KERN_DEBUG "%s: didn't sleep in parport_claim_or_block()\n",
                               dev->name);
#endif
                }

#ifdef PARPORT_DEBUG_SHARING
                if (dev->port->physport->cad != dev)
                        printk(KERN_DEBUG "%s: exiting parport_claim_or_block "
                               "but %s owns port!\n", dev->name,
                               dev->port->physport->cad ?
                               dev->port->physport->cad->name:"nobody");
#endif
        }
        dev->waiting = 0;
        return r;
}

/**
 *      parport_release - give up access to a parallel port device
 *      @dev: pointer to structure representing parallel port device
 *
 *      This function cannot fail, but it should not be called without
 *      the port claimed.  Similarly, if the port is already claimed
 *      you should not try claiming it again.
 **/

void parport_release(struct pardevice *dev)
{
        struct parport *port = dev->port->physport;
        struct pardevice *pd;
        unsigned long flags;

        /* Make sure that dev is the current device */
        write_lock_irqsave(&port->cad_lock, flags);
        if (port->cad != dev) {
                write_unlock_irqrestore (&port->cad_lock, flags);
                printk(KERN_WARNING "%s: %s tried to release parport "
                       "when not owner\n", port->name, dev->name);
                return;
        }

#ifdef CONFIG_PARPORT_1284
        /* If this is on a mux port, deselect it. */
        if (dev->port->muxport >= 0) {
                /* FIXME */
                port->muxsel = -1;
        }

        /* If this is a daisy device, deselect it. */
        if (dev->daisy >= 0) {
                parport_daisy_deselect_all (port);
                port->daisy = -1;
        }
#endif

        port->cad = NULL;
        write_unlock_irqrestore(&port->cad_lock, flags);

        /* Save control registers */
        port->ops->save_state(port, dev->state);

        /* If anybody is waiting, find out who's been there longest and
           then wake them up. (Note: no locking required) */
        /* !!! LOCKING IS NEEDED HERE */
        for (pd = port->waithead; pd; pd = pd->waitnext) {
                if (pd->waiting & 2) { /* sleeping in claim_or_block */
                        parport_claim(pd);
                        if (waitqueue_active(&pd->wait_q))
                                wake_up_interruptible(&pd->wait_q);
                        return;
                } else if (pd->wakeup) {
                        pd->wakeup(pd->private);
                        if (dev->port->cad) /* racy but no matter */
                                return;
                } else {
                        printk(KERN_ERR "%s: don't know how to wake %s\n", port->name, pd->name);
                }
        }

        /* Nobody was waiting, so walk the list to see if anyone is
           interested in being woken up. (Note: no locking required) */
        /* !!! LOCKING IS NEEDED HERE */
        for (pd = port->devices; (port->cad == NULL) && pd; pd = pd->next) {
                if (pd->wakeup && pd != dev)
                        pd->wakeup(pd->private);
        }
}

/* Exported symbols for modules. */

EXPORT_SYMBOL(parport_claim);
EXPORT_SYMBOL(parport_claim_or_block);
EXPORT_SYMBOL(parport_release);
EXPORT_SYMBOL(parport_register_port);
EXPORT_SYMBOL(parport_announce_port);
EXPORT_SYMBOL(parport_remove_port);
EXPORT_SYMBOL(parport_register_driver);
EXPORT_SYMBOL(parport_unregister_driver);
EXPORT_SYMBOL(parport_register_device);
EXPORT_SYMBOL(parport_unregister_device);
EXPORT_SYMBOL(parport_get_port);
EXPORT_SYMBOL(parport_put_port);
EXPORT_SYMBOL(parport_find_number);
EXPORT_SYMBOL(parport_find_base);

MODULE_LICENSE("GPL");