/*
 * vgaarb.c
 *
 * (C) Copyright 2005 Benjamin Herrenschmidt <benh@kernel.crashing.org>
 * (C) Copyright 2007 Paulo R. Zanoni <przanoni@gmail.com>
 * (C) Copyright 2007, 2009 Tiago Vignatti <vignatti@freedesktop.org>
 *
 * Implements the VGA arbitration. For details refer to
 * Documentation/vgaarbiter.txt
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/pci.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/spinlock.h>
#include <linux/poll.h>
#include <linux/miscdevice.h>

#include <linux/uaccess.h>

#include <linux/vgaarb.h>

static void vga_arbiter_notify_clients(void);
/*
 * We keep a list of all vga devices in the system to speed
 * up the various operations of the arbiter
 */
struct vga_device {
        struct list_head list;
        struct pci_dev *pdev;
        unsigned int decodes;   /* what does it decodes */
        unsigned int owns;      /* what does it owns */
        unsigned int locks;     /* what does it locks */
        unsigned int io_lock_cnt;       /* legacy IO lock count */
        unsigned int mem_lock_cnt;      /* legacy MEM lock count */
        unsigned int io_norm_cnt;       /* normal IO count */
        unsigned int mem_norm_cnt;      /* normal MEM count */

        /* allow IRQ enable/disable hook */
        void *cookie;
        void (*irq_set_state)(void *cookie, bool enable);
        unsigned int (*set_vga_decode)(void *cookie, bool decode);
};

static LIST_HEAD(vga_list);
static int vga_count, vga_decode_count;
static bool vga_arbiter_used;
static DEFINE_SPINLOCK(vga_lock);
static DECLARE_WAIT_QUEUE_HEAD(vga_wait_queue);


static const char *vga_iostate_to_str(unsigned int iostate)
{
        /* Ignore VGA_RSRC_IO and VGA_RSRC_MEM */
        iostate &= VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM;
        switch (iostate) {
        case VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM:
                return "io+mem";
        case VGA_RSRC_LEGACY_IO:
                return "io";
        case VGA_RSRC_LEGACY_MEM:
                return "mem";
        }
        return "none";
}

static int vga_str_to_iostate(char *buf, int str_size, int *io_state)
{
        /* we could in theory hand out locks on IO and mem
         * separately to userspace but it can cause deadlocks */
        if (strncmp(buf, "none", 4) == 0) {
                *io_state = VGA_RSRC_NONE;
                return 1;
        }

        /* XXX We're not chekcing the str_size! */
        if (strncmp(buf, "io+mem", 6) == 0)
                goto both;
        else if (strncmp(buf, "io", 2) == 0)
                goto both;
        else if (strncmp(buf, "mem", 3) == 0)
                goto both;
        return 0;
both:
        *io_state = VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM;
        return 1;
}

#ifndef __ARCH_HAS_VGA_DEFAULT_DEVICE
/* this is only used a cookie - it should not be dereferenced */
static struct pci_dev *vga_default;
#endif

static void vga_arb_device_card_gone(struct pci_dev *pdev);

/* Find somebody in our list */
static struct vga_device *vgadev_find(struct pci_dev *pdev)
{
        struct vga_device *vgadev;

        list_for_each_entry(vgadev, &vga_list, list)
                if (pdev == vgadev->pdev)
                        return vgadev;
        return NULL;
}

/* Returns the default VGA device (vgacon's babe) */
#ifndef __ARCH_HAS_VGA_DEFAULT_DEVICE
struct pci_dev *vga_default_device(void)
{
        return vga_default;
}
#endif

static inline void vga_irq_set_state(struct vga_device *vgadev, bool state)
{
        if (vgadev->irq_set_state)
                vgadev->irq_set_state(vgadev->cookie, state);
}


/* If we don't ever use VGA arb we should avoid
   turning off anything anywhere due to old X servers getting
   confused about the boot device not being VGA */
static void vga_check_first_use(void)
{
        /* we should inform all GPUs in the system that
         * VGA arb has occured and to try and disable resources
         * if they can */
        if (!vga_arbiter_used) {
                vga_arbiter_used = true;
                vga_arbiter_notify_clients();
        }
}

static struct vga_device *__vga_tryget(struct vga_device *vgadev,
                                       unsigned int rsrc)
{
        unsigned int wants, legacy_wants, match;
        struct vga_device *conflict;
        unsigned int pci_bits;
        /* Account for "normal" resources to lock. If we decode the legacy,
         * counterpart, we need to request it as well
         */
        if ((rsrc & VGA_RSRC_NORMAL_IO) &&
            (vgadev->decodes & VGA_RSRC_LEGACY_IO))
                rsrc |= VGA_RSRC_LEGACY_IO;
        if ((rsrc & VGA_RSRC_NORMAL_MEM) &&
            (vgadev->decodes & VGA_RSRC_LEGACY_MEM))
                rsrc |= VGA_RSRC_LEGACY_MEM;

        pr_devel("%s: %d\n", __func__, rsrc);
        pr_devel("%s: owns: %d\n", __func__, vgadev->owns);

        /* Check what resources we need to acquire */
        wants = rsrc & ~vgadev->owns;

        /* We already own everything, just mark locked & bye bye */
        if (wants == 0)
                goto lock_them;

        /* We don't need to request a legacy resource, we just enable
         * appropriate decoding and go
         */
        legacy_wants = wants & VGA_RSRC_LEGACY_MASK;
        if (legacy_wants == 0)
                goto enable_them;

        /* Ok, we don't, let's find out how we need to kick off */
        list_for_each_entry(conflict, &vga_list, list) {
                unsigned int lwants = legacy_wants;
                unsigned int change_bridge = 0;

                /* Don't conflict with myself */
                if (vgadev == conflict)
                        continue;

                /* Check if the architecture allows a conflict between those
                 * 2 devices or if they are on separate domains
                 */
                if (!vga_conflicts(vgadev->pdev, conflict->pdev))
                        continue;

                /* We have a possible conflict. before we go further, we must
                 * check if we sit on the same bus as the conflicting device.
                 * if we don't, then we must tie both IO and MEM resources
                 * together since there is only a single bit controlling
                 * VGA forwarding on P2P bridges
                 */
                if (vgadev->pdev->bus != conflict->pdev->bus) {
                        change_bridge = 1;
                        lwants = VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM;
                }

                /* Check if the guy has a lock on the resource. If he does,
                 * return the conflicting entry
                 */
                if (conflict->locks & lwants)
                        return conflict;

                /* Ok, now check if he owns the resource we want. We don't need
                 * to check "decodes" since it should be impossible to own
                 * own legacy resources you don't decode unless I have a bug
                 * in this code...
                 */
                WARN_ON(conflict->owns & ~conflict->decodes);
                match = lwants & conflict->owns;
                if (!match)
                        continue;

                /* looks like he doesn't have a lock, we can steal
                 * them from him
                 */
                vga_irq_set_state(conflict, false);

                pci_bits = 0;
                if (lwants & (VGA_RSRC_LEGACY_MEM|VGA_RSRC_NORMAL_MEM))
                        pci_bits |= PCI_COMMAND_MEMORY;
                if (lwants & (VGA_RSRC_LEGACY_IO|VGA_RSRC_NORMAL_IO))
                        pci_bits |= PCI_COMMAND_IO;

                pci_set_vga_state(conflict->pdev, false, pci_bits,
                                  change_bridge);
                conflict->owns &= ~lwants;
                /* If he also owned non-legacy, that is no longer the case */
                if (lwants & VGA_RSRC_LEGACY_MEM)
                        conflict->owns &= ~VGA_RSRC_NORMAL_MEM;
                if (lwants & VGA_RSRC_LEGACY_IO)
                        conflict->owns &= ~VGA_RSRC_NORMAL_IO;
        }

enable_them:
        /* ok dude, we got it, everybody conflicting has been disabled, let's
         * enable us. Make sure we don't mark a bit in "owns" that we don't
         * also have in "decodes". We can lock resources we don't decode but
         * not own them.
         */
        pci_bits = 0;
        if (wants & (VGA_RSRC_LEGACY_MEM|VGA_RSRC_NORMAL_MEM))
                pci_bits |= PCI_COMMAND_MEMORY;
        if (wants & (VGA_RSRC_LEGACY_IO|VGA_RSRC_NORMAL_IO))
                pci_bits |= PCI_COMMAND_IO;
        pci_set_vga_state(vgadev->pdev, true, pci_bits, !!(wants & VGA_RSRC_LEGACY_MASK));

        vga_irq_set_state(vgadev, true);
        vgadev->owns |= (wants & vgadev->decodes);
lock_them:
        vgadev->locks |= (rsrc & VGA_RSRC_LEGACY_MASK);
        if (rsrc & VGA_RSRC_LEGACY_IO)
                vgadev->io_lock_cnt++;
        if (rsrc & VGA_RSRC_LEGACY_MEM)
                vgadev->mem_lock_cnt++;
        if (rsrc & VGA_RSRC_NORMAL_IO)
                vgadev->io_norm_cnt++;
        if (rsrc & VGA_RSRC_NORMAL_MEM)
                vgadev->mem_norm_cnt++;

        return NULL;
}

static void __vga_put(struct vga_device *vgadev, unsigned int rsrc)
{
        unsigned int old_locks = vgadev->locks;

        pr_devel("%s\n", __func__);

        /* Update our counters, and account for equivalent legacy resources
         * if we decode them
         */
        if ((rsrc & VGA_RSRC_NORMAL_IO) && vgadev->io_norm_cnt > 0) {
                vgadev->io_norm_cnt--;
                if (vgadev->decodes & VGA_RSRC_LEGACY_IO)
                        rsrc |= VGA_RSRC_LEGACY_IO;
        }
        if ((rsrc & VGA_RSRC_NORMAL_MEM) && vgadev->mem_norm_cnt > 0) {
                vgadev->mem_norm_cnt--;
                if (vgadev->decodes & VGA_RSRC_LEGACY_MEM)
                        rsrc |= VGA_RSRC_LEGACY_MEM;
        }
        if ((rsrc & VGA_RSRC_LEGACY_IO) && vgadev->io_lock_cnt > 0)
                vgadev->io_lock_cnt--;
        if ((rsrc & VGA_RSRC_LEGACY_MEM) && vgadev->mem_lock_cnt > 0)
                vgadev->mem_lock_cnt--;

        /* Just clear lock bits, we do lazy operations so we don't really
         * have to bother about anything else at this point
         */
        if (vgadev->io_lock_cnt == 0)
                vgadev->locks &= ~VGA_RSRC_LEGACY_IO;
        if (vgadev->mem_lock_cnt == 0)
                vgadev->locks &= ~VGA_RSRC_LEGACY_MEM;

        /* Kick the wait queue in case somebody was waiting if we actually
         * released something
         */
        if (old_locks != vgadev->locks)
                wake_up_all(&vga_wait_queue);
}

int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
{
        struct vga_device *vgadev, *conflict;
        unsigned long flags;
        wait_queue_t wait;
        int rc = 0;

        vga_check_first_use();
        /* The one who calls us should check for this, but lets be sure... */
        if (pdev == NULL)
                pdev = vga_default_device();
        if (pdev == NULL)
                return 0;

        for (;;) {
                spin_lock_irqsave(&vga_lock, flags);
                vgadev = vgadev_find(pdev);
                if (vgadev == NULL) {
                        spin_unlock_irqrestore(&vga_lock, flags);
                        rc = -ENODEV;
                        break;
                }
                conflict = __vga_tryget(vgadev, rsrc);
                spin_unlock_irqrestore(&vga_lock, flags);
                if (conflict == NULL)
                        break;


                /* We have a conflict, we wait until somebody kicks the
                 * work queue. Currently we have one work queue that we
                 * kick each time some resources are released, but it would
                 * be fairly easy to have a per device one so that we only
                 * need to attach to the conflicting device
                 */
                init_waitqueue_entry(&wait, current);
                add_wait_queue(&vga_wait_queue, &wait);
                set_current_state(interruptible ?
                                  TASK_INTERRUPTIBLE :
                                  TASK_UNINTERRUPTIBLE);
                if (signal_pending(current)) {
                        rc = -EINTR;
                        break;
                }
                schedule();
                remove_wait_queue(&vga_wait_queue, &wait);
                set_current_state(TASK_RUNNING);
        }
        return rc;
}
EXPORT_SYMBOL(vga_get);

int vga_tryget(struct pci_dev *pdev, unsigned int rsrc)
{
        struct vga_device *vgadev;
        unsigned long flags;
        int rc = 0;

        vga_check_first_use();

        /* The one who calls us should check for this, but lets be sure... */
        if (pdev == NULL)
                pdev = vga_default_device();
        if (pdev == NULL)
                return 0;
        spin_lock_irqsave(&vga_lock, flags);
        vgadev = vgadev_find(pdev);
        if (vgadev == NULL) {
                rc = -ENODEV;
                goto bail;
        }
        if (__vga_tryget(vgadev, rsrc))
                rc = -EBUSY;
bail:
        spin_unlock_irqrestore(&vga_lock, flags);
        return rc;
}
EXPORT_SYMBOL(vga_tryget);

void vga_put(struct pci_dev *pdev, unsigned int rsrc)
{
        struct vga_device *vgadev;
        unsigned long flags;

        /* The one who calls us should check for this, but lets be sure... */
        if (pdev == NULL)
                pdev = vga_default_device();
        if (pdev == NULL)
                return;
        spin_lock_irqsave(&vga_lock, flags);
        vgadev = vgadev_find(pdev);
        if (vgadev == NULL)
                goto bail;
        __vga_put(vgadev, rsrc);
bail:
        spin_unlock_irqrestore(&vga_lock, flags);
}
EXPORT_SYMBOL(vga_put);

/*
 * Currently, we assume that the "initial" setup of the system is
 * not sane, that is we come up with conflicting devices and let
 * the arbiter's client decides if devices decodes or not legacy
 * things.
 */
static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
{
        struct vga_device *vgadev;
        unsigned long flags;
        struct pci_bus *bus;
        struct pci_dev *bridge;
        u16 cmd;

        /* Only deal with VGA class devices */
        if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
                return false;

        /* Allocate structure */
        vgadev = kmalloc(sizeof(struct vga_device), GFP_KERNEL);
        if (vgadev == NULL) {
                pr_err("vgaarb: failed to allocate pci device\n");
                /* What to do on allocation failure ? For now, let's
                 * just do nothing, I'm not sure there is anything saner
                 * to be done
                 */
                return false;
        }

        memset(vgadev, 0, sizeof(*vgadev));

        /* Take lock & check for duplicates */
        spin_lock_irqsave(&vga_lock, flags);
        if (vgadev_find(pdev) != NULL) {
                BUG_ON(1);
                goto fail;
        }
        vgadev->pdev = pdev;

        /* By default, assume we decode everything */
        vgadev->decodes = VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM |
                          VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM;

        /* by default mark it as decoding */
        vga_decode_count++;
        /* Mark that we "own" resources based on our enables, we will
         * clear that below if the bridge isn't forwarding
         */
        pci_read_config_word(pdev, PCI_COMMAND, &cmd);
        if (cmd & PCI_COMMAND_IO)
                vgadev->owns |= VGA_RSRC_LEGACY_IO;
        if (cmd & PCI_COMMAND_MEMORY)
                vgadev->owns |= VGA_RSRC_LEGACY_MEM;

        /* Check if VGA cycles can get down to us */
        bus = pdev->bus;
        while (bus) {
                bridge = bus->self;
                if (bridge) {
                        u16 l;
                        pci_read_config_word(bridge, PCI_BRIDGE_CONTROL,
                                             &l);
                        if (!(l & PCI_BRIDGE_CTL_VGA)) {
                                vgadev->owns = 0;
                                break;
                        }
                }
                bus = bus->parent;
        }

        /* Deal with VGA default device. Use first enabled one
         * by default if arch doesn't have it's own hook
         */
#ifndef __ARCH_HAS_VGA_DEFAULT_DEVICE
        if (vga_default == NULL &&
            ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK))
                vga_default = pci_dev_get(pdev);
#endif

        /* Add to the list */
        list_add(&vgadev->list, &vga_list);
        vga_count++;
        pr_info("vgaarb: device added: PCI:%s,decodes=%s,owns=%s,locks=%s\n",
                pci_name(pdev),
                vga_iostate_to_str(vgadev->decodes),
                vga_iostate_to_str(vgadev->owns),
                vga_iostate_to_str(vgadev->locks));

        spin_unlock_irqrestore(&vga_lock, flags);
        return true;
fail:
        spin_unlock_irqrestore(&vga_lock, flags);
        kfree(vgadev);
        return false;
}

static bool vga_arbiter_del_pci_device(struct pci_dev *pdev)
{
        struct vga_device *vgadev;
        unsigned long flags;
        bool ret = true;

        spin_lock_irqsave(&vga_lock, flags);
        vgadev = vgadev_find(pdev);
        if (vgadev == NULL) {
                ret = false;
                goto bail;
        }

        if (vga_default == pdev) {
                pci_dev_put(vga_default);
                vga_default = NULL;
        }

        if (vgadev->decodes & (VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM))
                vga_decode_count--;

        /* Remove entry from list */
        list_del(&vgadev->list);
        vga_count--;
        /* Notify userland driver that the device is gone so it discards
         * it's copies of the pci_dev pointer
         */
        vga_arb_device_card_gone(pdev);

        /* Wake up all possible waiters */
        wake_up_all(&vga_wait_queue);
bail:
        spin_unlock_irqrestore(&vga_lock, flags);
        kfree(vgadev);
        return ret;
}

/* this is called with the lock */
static inline void vga_update_device_decodes(struct vga_device *vgadev,
                                             int new_decodes)
{
        int old_decodes;
        struct vga_device *new_vgadev, *conflict;

        old_decodes = vgadev->decodes;
        vgadev->decodes = new_decodes;

        pr_info("vgaarb: device changed decodes: PCI:%s,olddecodes=%s,decodes=%s:owns=%s\n",
                pci_name(vgadev->pdev),
                vga_iostate_to_str(old_decodes),
                vga_iostate_to_str(vgadev->decodes),
                vga_iostate_to_str(vgadev->owns));


        /* if we own the decodes we should move them along to
           another card */
        if ((vgadev->owns & old_decodes) && (vga_count > 1)) {
                /* set us to own nothing */
                vgadev->owns &= ~old_decodes;
                list_for_each_entry(new_vgadev, &vga_list, list) {
                        if ((new_vgadev != vgadev) &&
                            (new_vgadev->decodes & VGA_RSRC_LEGACY_MASK)) {
                                pr_info("vgaarb: transferring owner from PCI:%s to PCI:%s\n", pci_name(vgadev->pdev), pci_name(new_vgadev->pdev));
                                conflict = __vga_tryget(new_vgadev, VGA_RSRC_LEGACY_MASK);
                                if (!conflict)
                                        __vga_put(new_vgadev, VGA_RSRC_LEGACY_MASK);
                                break;
                        }
                }
        }

        /* change decodes counter */
        if (old_decodes != new_decodes) {
                if (new_decodes & (VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM))
                        vga_decode_count++;
                else
                        vga_decode_count--;
        }
}

void __vga_set_legacy_decoding(struct pci_dev *pdev, unsigned int decodes, bool userspace)
{
        struct vga_device *vgadev;
        unsigned long flags;

        decodes &= VGA_RSRC_LEGACY_MASK;

        spin_lock_irqsave(&vga_lock, flags);
        vgadev = vgadev_find(pdev);
        if (vgadev == NULL)
                goto bail;

        /* don't let userspace futz with kernel driver decodes */
        if (userspace && vgadev->set_vga_decode)
                goto bail;

        /* update the device decodes + counter */
        vga_update_device_decodes(vgadev, decodes);

        /* XXX if somebody is going from "doesn't decode" to "decodes" state
         * here, additional care must be taken as we may have pending owner
         * ship of non-legacy region ...
         */
bail:
        spin_unlock_irqrestore(&vga_lock, flags);
}

void vga_set_legacy_decoding(struct pci_dev *pdev, unsigned int decodes)
{
        __vga_set_legacy_decoding(pdev, decodes, false);
}
EXPORT_SYMBOL(vga_set_legacy_decoding);

/* call with NULL to unregister */
int vga_client_register(struct pci_dev *pdev, void *cookie,
                        void (*irq_set_state)(void *cookie, bool state),
                        unsigned int (*set_vga_decode)(void *cookie, bool decode))
{
        int ret = -1;
        struct vga_device *vgadev;
        unsigned long flags;

        spin_lock_irqsave(&vga_lock, flags);
        vgadev = vgadev_find(pdev);
        if (!vgadev)
                goto bail;

        vgadev->irq_set_state = irq_set_state;
        vgadev->set_vga_decode = set_vga_decode;
        vgadev->cookie = cookie;
        ret = 0;

bail:
        spin_unlock_irqrestore(&vga_lock, flags);
        return ret;

}
EXPORT_SYMBOL(vga_client_register);

/*
 * Char driver implementation
 *
 * Semantics is:
 *
 *  open       : open user instance of the arbitrer. by default, it's
 *                attached to the default VGA device of the system.
 *
 *  close      : close user instance, release locks
 *
 *  read       : return a string indicating the status of the target.
 *                an IO state string is of the form {io,mem,io+mem,none},
 *                mc and ic are respectively mem and io lock counts (for
 *                debugging/diagnostic only). "decodes" indicate what the
 *                card currently decodes, "owns" indicates what is currently
 *                enabled on it, and "locks" indicates what is locked by this
 *                card. If the card is unplugged, we get "invalid" then for
 *                card_ID and an -ENODEV error is returned for any command
 *                until a new card is targeted
 *
 *   "<card_ID>,decodes=<io_state>,owns=<io_state>,locks=<io_state> (ic,mc)"
 *
 * write       : write a command to the arbiter. List of commands is:
 *
 *   target <card_ID>   : switch target to card <card_ID> (see below)
 *   lock <io_state>    : acquires locks on target ("none" is invalid io_state)
 *   trylock <io_state> : non-blocking acquire locks on target
 *   unlock <io_state>  : release locks on target
 *   unlock all         : release all locks on target held by this user
 *   decodes <io_state> : set the legacy decoding attributes for the card
 *
 * poll         : event if something change on any card (not just the target)
 *
 * card_ID is of the form "PCI:domain:bus:dev.fn". It can be set to "default"
 * to go back to the system default card (TODO: not implemented yet).
 * Currently, only PCI is supported as a prefix, but the userland API may
 * support other bus types in the future, even if the current kernel
 * implementation doesn't.
 *
 * Note about locks:
 *
 * The driver keeps track of which user has what locks on which card. It
 * supports stacking, like the kernel one. This complexifies the implementation
 * a bit, but makes the arbiter more tolerant to userspace problems and able
 * to properly cleanup in all cases when a process dies.
 * Currently, a max of 16 cards simultaneously can have locks issued from
 * userspace for a given user (file descriptor instance) of the arbiter.
 *
 * If the device is hot-unplugged, there is a hook inside the module to notify
 * they being added/removed in the system and automatically added/removed in
 * the arbiter.
 */

#define MAX_USER_CARDS         16
#define PCI_INVALID_CARD       ((struct pci_dev *)-1UL)

/*
 * Each user has an array of these, tracking which cards have locks
 */
struct vga_arb_user_card {
        struct pci_dev *pdev;
        unsigned int mem_cnt;
        unsigned int io_cnt;
};

struct vga_arb_private {
        struct list_head list;
        struct pci_dev *target;
        struct vga_arb_user_card cards[MAX_USER_CARDS];
        spinlock_t lock;
};

static LIST_HEAD(vga_user_list);
static DEFINE_SPINLOCK(vga_user_lock);


/*
 * This function gets a string in the format: "PCI:domain:bus:dev.fn" and
 * returns the respective values. If the string is not in this format,
 * it returns 0.
 */
static int vga_pci_str_to_vars(char *buf, int count, unsigned int *domain,
                               unsigned int *bus, unsigned int *devfn)
{
        int n;
        unsigned int slot, func;


        n = sscanf(buf, "PCI:%x:%x:%x.%x", domain, bus, &slot, &func);
        if (n != 4)
                return 0;

        *devfn = PCI_DEVFN(slot, func);

        return 1;
}

static ssize_t vga_arb_read(struct file *file, char __user * buf,
                            size_t count, loff_t *ppos)
{
        struct vga_arb_private *priv = file->private_data;
        struct vga_device *vgadev;
        struct pci_dev *pdev;
        unsigned long flags;
        size_t len;
        int rc;
        char *lbuf;

        lbuf = kmalloc(1024, GFP_KERNEL);
        if (lbuf == NULL)
                return -ENOMEM;

        /* Shields against vga_arb_device_card_gone (pci_dev going
         * away), and allows access to vga list
         */
        spin_lock_irqsave(&vga_lock, flags);

        /* If we are targetting the default, use it */
        pdev = priv->target;
        if (pdev == NULL || pdev == PCI_INVALID_CARD) {
                spin_unlock_irqrestore(&vga_lock, flags);
                len = sprintf(lbuf, "invalid");
                goto done;
        }

        /* Find card vgadev structure */
        vgadev = vgadev_find(pdev);
        if (vgadev == NULL) {
                /* Wow, it's not in the list, that shouldn't happen,
                 * let's fix us up and return invalid card
                 */
                if (pdev == priv->target)
                        vga_arb_device_card_gone(pdev);
                spin_unlock_irqrestore(&vga_lock, flags);
                len = sprintf(lbuf, "invalid");
                goto done;
        }

        /* Fill the buffer with infos */
        len = snprintf(lbuf, 1024,
                       "count:%d,PCI:%s,decodes=%s,owns=%s,locks=%s(%d:%d)\n",
                       vga_decode_count, pci_name(pdev),
                       vga_iostate_to_str(vgadev->decodes),
                       vga_iostate_to_str(vgadev->owns),
                       vga_iostate_to_str(vgadev->locks),
                       vgadev->io_lock_cnt, vgadev->mem_lock_cnt);

        spin_unlock_irqrestore(&vga_lock, flags);
done:

        /* Copy that to user */
        if (len > count)
                len = count;
        rc = copy_to_user(buf, lbuf, len);
        kfree(lbuf);
        if (rc)
                return -EFAULT;
        return len;
}

/*
 * TODO: To avoid parsing inside kernel and to improve the speed we may
 * consider use ioctl here
 */
static ssize_t vga_arb_write(struct file *file, const char __user * buf,
                             size_t count, loff_t *ppos)
{
        struct vga_arb_private *priv = file->private_data;
        struct vga_arb_user_card *uc = NULL;
        struct pci_dev *pdev;

        unsigned int io_state;

        char *kbuf, *curr_pos;
        size_t remaining = count;

        int ret_val;
        int i;


        kbuf = kmalloc(count + 1, GFP_KERNEL);
        if (!kbuf)
                return -ENOMEM;

        if (copy_from_user(kbuf, buf, count)) {
                kfree(kbuf);
                return -EFAULT;
        }
        curr_pos = kbuf;
        kbuf[count] = '\0';     /* Just to make sure... */

        if (strncmp(curr_pos, "lock ", 5) == 0) {
                curr_pos += 5;
                remaining -= 5;

                pr_devel("client 0x%p called 'lock'\n", priv);

                if (!vga_str_to_iostate(curr_pos, remaining, &io_state)) {
                        ret_val = -EPROTO;
                        goto done;
                }
                if (io_state == VGA_RSRC_NONE) {
                        ret_val = -EPROTO;
                        goto done;
                }

                pdev = priv->target;
                if (priv->target == NULL) {
                        ret_val = -ENODEV;
                        goto done;
                }

                vga_get_uninterruptible(pdev, io_state);

                /* Update the client's locks lists... */
                for (i = 0; i < MAX_USER_CARDS; i++) {
                        if (priv->cards[i].pdev == pdev) {
                                if (io_state & VGA_RSRC_LEGACY_IO)
                                        priv->cards[i].io_cnt++;
                                if (io_state & VGA_RSRC_LEGACY_MEM)
                                        priv->cards[i].mem_cnt++;
                                break;
                        }
                }

                ret_val = count;
                goto done;
        } else if (strncmp(curr_pos, "unlock ", 7) == 0) {
                curr_pos += 7;
                remaining -= 7;

                pr_devel("client 0x%p called 'unlock'\n", priv);

                if (strncmp(curr_pos, "all", 3) == 0)
                        io_state = VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM;
                else {
                        if (!vga_str_to_iostate
                            (curr_pos, remaining, &io_state)) {
                                ret_val = -EPROTO;
                                goto done;
                        }
                        /* TODO: Add this?
                           if (io_state == VGA_RSRC_NONE) {
                           ret_val = -EPROTO;
                           goto done;
                           }
                          */
                }

                pdev = priv->target;
                if (priv->target == NULL) {
                        ret_val = -ENODEV;
                        goto done;
                }
                for (i = 0; i < MAX_USER_CARDS; i++) {
                        if (priv->cards[i].pdev == pdev)
                                uc = &priv->cards[i];
                }

                if (!uc)
                        return -EINVAL;

                if (io_state & VGA_RSRC_LEGACY_IO && uc->io_cnt == 0)
                        return -EINVAL;

                if (io_state & VGA_RSRC_LEGACY_MEM && uc->mem_cnt == 0)
                        return -EINVAL;

                vga_put(pdev, io_state);

                if (io_state & VGA_RSRC_LEGACY_IO)
                        uc->io_cnt--;
                if (io_state & VGA_RSRC_LEGACY_MEM)
                        uc->mem_cnt--;

                ret_val = count;
                goto done;
        } else if (strncmp(curr_pos, "trylock ", 8) == 0) {
                curr_pos += 8;
                remaining -= 8;

                pr_devel("client 0x%p called 'trylock'\n", priv);

                if (!vga_str_to_iostate(curr_pos, remaining, &io_state)) {
                        ret_val = -EPROTO;
                        goto done;
                }
                /* TODO: Add this?
                   if (io_state == VGA_RSRC_NONE) {
                   ret_val = -EPROTO;
                   goto done;
                   }
                 */

                pdev = priv->target;
                if (priv->target == NULL) {
                        ret_val = -ENODEV;
                        goto done;
                }

                if (vga_tryget(pdev, io_state)) {
                        /* Update the client's locks lists... */
                        for (i = 0; i < MAX_USER_CARDS; i++) {
                                if (priv->cards[i].pdev == pdev) {
                                        if (io_state & VGA_RSRC_LEGACY_IO)
                                                priv->cards[i].io_cnt++;
                                        if (io_state & VGA_RSRC_LEGACY_MEM)
                                                priv->cards[i].mem_cnt++;
                                        break;
                                }
                        }
                        ret_val = count;
                        goto done;
                } else {
                        ret_val = -EBUSY;
                        goto done;
                }

        } else if (strncmp(curr_pos, "target ", 7) == 0) {
                unsigned int domain, bus, devfn;
                struct vga_device *vgadev;

                curr_pos += 7;
                remaining -= 7;
                pr_devel("client 0x%p called 'target'\n", priv);
                /* if target is default */
                if (!strncmp(buf, "default", 7))
                        pdev = pci_dev_get(vga_default_device());
                else {
                        if (!vga_pci_str_to_vars(curr_pos, remaining,
                                                 &domain, &bus, &devfn)) {
                                ret_val = -EPROTO;
                                goto done;
                        }

                        pdev = pci_get_bus_and_slot(bus, devfn);
                        if (!pdev) {
                                pr_info("vgaarb: invalid PCI address!\n");
                                ret_val = -ENODEV;
                                goto done;
                        }
                }

                vgadev = vgadev_find(pdev);
                if (vgadev == NULL) {
                        pr_info("vgaarb: this pci device is not a vga device\n");
                        pci_dev_put(pdev);
                        ret_val = -ENODEV;
                        goto done;
                }

                priv->target = pdev;
                for (i = 0; i < MAX_USER_CARDS; i++) {
                        if (priv->cards[i].pdev == pdev)
                                break;
                        if (priv->cards[i].pdev == NULL) {
                                priv->cards[i].pdev = pdev;
                                priv->cards[i].io_cnt = 0;
                                priv->cards[i].mem_cnt = 0;
                                break;
                        }
                }
                if (i == MAX_USER_CARDS) {

                        pr_err("vgaarb: maximum user cards number reached!\n");
                        pci_dev_put(pdev);
                        /* XXX: which value to return? */
                        ret_val =  -ENOMEM;
                        goto done;
                }

                ret_val = count;
                pci_dev_put(pdev);
                goto done;


        } else if (strncmp(curr_pos, "decodes ", 8) == 0) {
                curr_pos += 8;
                remaining -= 8;
                pr_devel("vgaarb: client 0x%p called 'decodes'\n", priv);

                if (!vga_str_to_iostate(curr_pos, remaining, &io_state)) {
                        ret_val = -EPROTO;
                        goto done;
                }
                pdev = priv->target;
                if (priv->target == NULL) {
                        ret_val = -ENODEV;
                        goto done;
                }

                __vga_set_legacy_decoding(pdev, io_state, true);
                ret_val = count;
                goto done;
        }
        /* If we got here, the message written is not part of the protocol! */
        kfree(kbuf);
        return -EPROTO;

done:
        kfree(kbuf);
        return ret_val;
}

static unsigned int vga_arb_fpoll(struct file *file, poll_table * wait)
{
        struct vga_arb_private *priv = file->private_data;

        pr_devel("%s\n", __func__);

        if (priv == NULL)
                return -ENODEV;
        poll_wait(file, &vga_wait_queue, wait);
        return POLLIN;
}

static int vga_arb_open(struct inode *inode, struct file *file)
{
        struct vga_arb_private *priv;
        unsigned long flags;

        pr_devel("%s\n", __func__);

        priv = kmalloc(sizeof(struct vga_arb_private), GFP_KERNEL);
        if (priv == NULL)
                return -ENOMEM;
        memset(priv, 0, sizeof(*priv));
        spin_lock_init(&priv->lock);
        file->private_data = priv;

        spin_lock_irqsave(&vga_user_lock, flags);
        list_add(&priv->list, &vga_user_list);
        spin_unlock_irqrestore(&vga_user_lock, flags);

        /* Set the client' lists of locks */
        priv->target = vga_default_device(); /* Maybe this is still null! */
        priv->cards[0].pdev = priv->target;
        priv->cards[0].io_cnt = 0;
        priv->cards[0].mem_cnt = 0;


        return 0;
}

static int vga_arb_release(struct inode *inode, struct file *file)
{
        struct vga_arb_private *priv = file->private_data;
        struct vga_arb_user_card *uc;
        unsigned long flags;
        int i;

        pr_devel("%s\n", __func__);

        if (priv == NULL)
                return -ENODEV;

        spin_lock_irqsave(&vga_user_lock, flags);
        list_del(&priv->list);
        for (i = 0; i < MAX_USER_CARDS; i++) {
                uc = &priv->cards[i];
                if (uc->pdev == NULL)
                        continue;
                pr_devel("uc->io_cnt == %d, uc->mem_cnt == %d\n",
                         uc->io_cnt, uc->mem_cnt);
                while (uc->io_cnt--)
                        vga_put(uc->pdev, VGA_RSRC_LEGACY_IO);
                while (uc->mem_cnt--)
                        vga_put(uc->pdev, VGA_RSRC_LEGACY_MEM);
        }
        spin_unlock_irqrestore(&vga_user_lock, flags);

        kfree(priv);

        return 0;
}

static void vga_arb_device_card_gone(struct pci_dev *pdev)
{
}

/*
 * callback any registered clients to let them know we have a
 * change in VGA cards
 */
static void vga_arbiter_notify_clients(void)
{
        struct vga_device *vgadev;
        unsigned long flags;
        uint32_t new_decodes;
        bool new_state;

        if (!vga_arbiter_used)
                return;

        spin_lock_irqsave(&vga_lock, flags);
        list_for_each_entry(vgadev, &vga_list, list) {
                if (vga_count > 1)
                        new_state = false;
                else
                        new_state = true;
                if (vgadev->set_vga_decode) {
                        new_decodes = vgadev->set_vga_decode(vgadev->cookie, new_state);
                        vga_update_device_decodes(vgadev, new_decodes);
                }
        }
        spin_unlock_irqrestore(&vga_lock, flags);
}

static int pci_notify(struct notifier_block *nb, unsigned long action,
                      void *data)
{
        struct device *dev = data;
        struct pci_dev *pdev = to_pci_dev(dev);
        bool notify = false;

        pr_devel("%s\n", __func__);

        /* For now we're only intereted in devices added and removed. I didn't
         * test this thing here, so someone needs to double check for the
         * cases of hotplugable vga cards. */
        if (action == BUS_NOTIFY_ADD_DEVICE)
                notify = vga_arbiter_add_pci_device(pdev);
        else if (action == BUS_NOTIFY_DEL_DEVICE)
                notify = vga_arbiter_del_pci_device(pdev);

        if (notify)
                vga_arbiter_notify_clients();
        return 0;
}

static struct notifier_block pci_notifier = {
        .notifier_call = pci_notify,
};

static const struct file_operations vga_arb_device_fops = {
        .read = vga_arb_read,
        .write = vga_arb_write,
        .poll = vga_arb_fpoll,
        .open = vga_arb_open,
        .release = vga_arb_release,
};

static struct miscdevice vga_arb_device = {
        MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
};

static int __init vga_arb_device_init(void)
{
        int rc;
        struct pci_dev *pdev;

        rc = misc_register(&vga_arb_device);
        if (rc < 0)
                pr_err("vgaarb: error %d registering device\n", rc);

        bus_register_notifier(&pci_bus_type, &pci_notifier);

        /* We add all pci devices satisfying vga class in the arbiter by
         * default */
        pdev = NULL;
        while ((pdev =
                pci_get_subsys(PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID,
                               PCI_ANY_ID, pdev)) != NULL)
                vga_arbiter_add_pci_device(pdev);

        pr_info("vgaarb: loaded\n");
        return rc;
}
subsys_initcall(vga_arb_device_init);