kernel / drivers / gpu / vga / vgaarb.c

/*
 * vgaarb.c
 *
 * (C) Copyright 2005 Benjamin Herrenschmidt <[e-mail]>
 * (C) Copyright 2007 Paulo R. Zanoni <[e-mail]>
 * (C) Copyright 2007, 2009 Tiago Vignatti <[e-mail]>
 *
 * 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);