PCI/VGA: Move vgaarb to drivers/pci

The VGA arbiter is really PCI-specific and doesn't depend on any GPU
things.  Move it to the PCI subsystem.

Note that misc_init() must be called before vga_arb_device_init().  These
are both subsys_initcalls, so this ordering depends on the link order,
which is determined by drivers/Makefile:

  obj-y += pci/
  obj-y += char/        <-- misc_init()
  obj-y += gpu/         <-- vga_arb_device_init() (before this commit)

The drivers/pci/ subsys_initcalls are called *before* misc_init(), so
convert vga_arb_device_init() to subsys_initcall_sync(), which is called
after *all* subsys_initcalls.

Link: https://lore.kernel.org/r/20220224224753.297579-2-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 1567 insertions, 0 deletions

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
new file mode 100644
index 000000000000..8320385a487b
--- /dev/null
+++ b/drivers/pci/vgaarb.c
@@ -0,0 +1,1567 @@
+/*
+ * vgaarb.c: Implements the VGA arbitration. For details refer to
+ * Documentation/gpu/vgaarbiter.rst
+ *
+ *
+ * (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>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#define pr_fmt(fmt) "vgaarb: " fmt
+
+#define vgaarb_dbg(dev, fmt, arg...)	dev_dbg(dev, "vgaarb: " fmt, ##arg)
+#define vgaarb_info(dev, fmt, arg...)	dev_info(dev, "vgaarb: " fmt, ##arg)
+#define vgaarb_err(dev, fmt, arg...)	dev_err(dev, "vgaarb: " fmt, ##arg)
+
+#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/signal.h>
+#include <linux/wait.h>
+#include <linux/spinlock.h>
+#include <linux/poll.h>
+#include <linux/miscdevice.h>
+#include <linux/slab.h>
+#include <linux/screen_info.h>
+#include <linux/vt.h>
+#include <linux/console.h>
+#include <linux/acpi.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 */
+	bool bridge_has_one_vga;
+	unsigned int (*set_decode)(struct pci_dev *pdev, 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;
+}
+
+/* this is only used a cookie - it should not be dereferenced */
+static struct pci_dev *vga_default;
+
+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;
+}
+
+/**
+ * vga_default_device - return the default VGA device, for vgacon
+ *
+ * This can be defined by the platform. The default implementation
+ * is rather dumb and will probably only work properly on single
+ * vga card setups and/or x86 platforms.
+ *
+ * If your VGA default device is not PCI, you'll have to return
+ * NULL here. In this case, I assume it will not conflict with
+ * any PCI card. If this is not true, I'll have to define two archs
+ * hooks for enabling/disabling the VGA default device if that is
+ * possible. This may be a problem with real _ISA_ VGA cards, in
+ * addition to a PCI one. I don't know at this point how to deal
+ * with that card. Can theirs IOs be disabled at all ? If not, then
+ * I suppose it's a matter of having the proper arch hook telling
+ * us about it, so we basically never allow anybody to succeed a
+ * vga_get()...
+ */
+struct pci_dev *vga_default_device(void)
+{
+	return vga_default;
+}
+EXPORT_SYMBOL_GPL(vga_default_device);
+
+void vga_set_default_device(struct pci_dev *pdev)
+{
+	if (vga_default == pdev)
+		return;
+
+	pci_dev_put(vga_default);
+	vga_default = pci_dev_get(pdev);
+}
+
+/**
+ * vga_remove_vgacon - deactivete vga console
+ *
+ * Unbind and unregister vgacon in case pdev is the default vga
+ * device.  Can be called by gpu drivers on initialization to make
+ * sure vga register access done by vgacon will not disturb the
+ * device.
+ *
+ * @pdev: pci device.
+ */
+#if !defined(CONFIG_VGA_CONSOLE)
+int vga_remove_vgacon(struct pci_dev *pdev)
+{
+	return 0;
+}
+#elif !defined(CONFIG_DUMMY_CONSOLE)
+int vga_remove_vgacon(struct pci_dev *pdev)
+{
+	return -ENODEV;
+}
+#else
+int vga_remove_vgacon(struct pci_dev *pdev)
+{
+	int ret = 0;
+
+	if (pdev != vga_default)
+		return 0;
+	vgaarb_info(&pdev->dev, "deactivate vga console\n");
+
+	console_lock();
+	if (con_is_bound(&vga_con))
+		ret = do_take_over_console(&dummy_con, 0,
+					   MAX_NR_CONSOLES - 1, 1);
+	if (ret == 0) {
+		ret = do_unregister_con_driver(&vga_con);
+
+		/* Ignore "already unregistered". */
+		if (ret == -ENODEV)
+			ret = 0;
+	}
+	console_unlock();
+
+	return ret;
+}
+#endif
+EXPORT_SYMBOL(vga_remove_vgacon);
+
+/* 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 occurred 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)
+{
+	struct device *dev = &vgadev->pdev->dev;
+	unsigned int wants, legacy_wants, match;
+	struct vga_device *conflict;
+	unsigned int pci_bits;
+	u32 flags = 0;
+
+	/* 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;
+
+	vgaarb_dbg(dev, "%s: %d\n", __func__, rsrc);
+	vgaarb_dbg(dev, "%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;
+
+		/* 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 it owns the resource we want.  We can
+		 * lock resources that are not decoded, therefore a device
+		 * can own resources it doesn't decode.
+		 */
+		match = lwants & conflict->owns;
+		if (!match)
+			continue;
+
+		/* looks like he doesn't have a lock, we can steal
+		 * them from him
+		 */
+
+		flags = 0;
+		pci_bits = 0;
+
+		/* If we can't control legacy resources via the bridge, we
+		 * also need to disable normal decoding.
+		 */
+		if (!conflict->bridge_has_one_vga) {
+			if ((match & conflict->decodes) & VGA_RSRC_LEGACY_MEM)
+				pci_bits |= PCI_COMMAND_MEMORY;
+			if ((match & conflict->decodes) & VGA_RSRC_LEGACY_IO)
+				pci_bits |= PCI_COMMAND_IO;
+
+			if (pci_bits)
+				flags |= PCI_VGA_STATE_CHANGE_DECODES;
+		}
+
+		if (change_bridge)
+			flags |= PCI_VGA_STATE_CHANGE_BRIDGE;
+
+		pci_set_vga_state(conflict->pdev, false, pci_bits, flags);
+		conflict->owns &= ~match;
+
+		/* If we disabled normal decoding, reflect it in owns */
+		if (pci_bits & PCI_COMMAND_MEMORY)
+			conflict->owns &= ~VGA_RSRC_NORMAL_MEM;
+		if (pci_bits & PCI_COMMAND_IO)
+			conflict->owns &= ~VGA_RSRC_NORMAL_IO;
+	}
+
+enable_them:
+	/* ok dude, we got it, everybody conflicting has been disabled, let's
+	 * enable us.  Mark any bits in "owns" regardless of whether we
+	 * decoded them.  We can lock resources we don't decode, therefore
+	 * we must track them via "owns".
+	 */
+	flags = 0;
+	pci_bits = 0;
+
+	if (!vgadev->bridge_has_one_vga) {
+		flags |= PCI_VGA_STATE_CHANGE_DECODES;
+		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;
+	}
+	if (wants & VGA_RSRC_LEGACY_MASK)
+		flags |= PCI_VGA_STATE_CHANGE_BRIDGE;
+
+	pci_set_vga_state(vgadev->pdev, true, pci_bits, flags);
+
+	vgadev->owns |= wants;
+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)
+{
+	struct device *dev = &vgadev->pdev->dev;
+	unsigned int old_locks = vgadev->locks;
+
+	vgaarb_dbg(dev, "%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);
+}
+
+/**
+ * vga_get - acquire & locks VGA resources
+ * @pdev: pci device of the VGA card or NULL for the system default
+ * @rsrc: bit mask of resources to acquire and lock
+ * @interruptible: blocking should be interruptible by signals ?
+ *
+ * This function acquires VGA resources for the given card and mark those
+ * resources locked. If the resource requested are "normal" (and not legacy)
+ * resources, the arbiter will first check whether the card is doing legacy
+ * decoding for that type of resource. If yes, the lock is "converted" into a
+ * legacy resource lock.
+ *
+ * The arbiter will first look for all VGA cards that might conflict and disable
+ * their IOs and/or Memory access, including VGA forwarding on P2P bridges if
+ * necessary, so that the requested resources can be used. Then, the card is
+ * marked as locking these resources and the IO and/or Memory accesses are
+ * enabled on the card (including VGA forwarding on parent P2P bridges if any).
+ *
+ * This function will block if some conflicting card is already locking one of
+ * the required resources (or any resource on a different bus segment, since P2P
+ * bridges don't differentiate VGA memory and IO afaik). You can indicate
+ * whether this blocking should be interruptible by a signal (for userland
+ * interface) or not.
+ *
+ * Must not be called at interrupt time or in atomic context.  If the card
+ * already owns the resources, the function succeeds.  Nested calls are
+ * supported (a per-resource counter is maintained)
+ *
+ * On success, release the VGA resource again with vga_put().
+ *
+ * Returns:
+ *
+ * 0 on success, negative error code on failure.
+ */
+int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
+{
+	struct vga_device *vgadev, *conflict;
+	unsigned long flags;
+	wait_queue_entry_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 (interruptible && signal_pending(current)) {
+			__set_current_state(TASK_RUNNING);
+			remove_wait_queue(&vga_wait_queue, &wait);
+			rc = -ERESTARTSYS;
+			break;
+		}
+		schedule();
+		remove_wait_queue(&vga_wait_queue, &wait);
+	}
+	return rc;
+}
+EXPORT_SYMBOL(vga_get);
+
+/**
+ * vga_tryget - try to acquire & lock legacy VGA resources
+ * @pdev: pci devivce of VGA card or NULL for system default
+ * @rsrc: bit mask of resources to acquire and lock
+ *
+ * This function performs the same operation as vga_get(), but will return an
+ * error (-EBUSY) instead of blocking if the resources are already locked by
+ * another card. It can be called in any context
+ *
+ * On success, release the VGA resource again with vga_put().
+ *
+ * Returns:
+ *
+ * 0 on success, negative error code on failure.
+ */
+static 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;
+}
+
+/**
+ * vga_put - release lock on legacy VGA resources
+ * @pdev: pci device of VGA card or NULL for system default
+ * @rsrc: but mask of resource to release
+ *
+ * This fuction releases resources previously locked by vga_get() or
+ * vga_tryget(). The resources aren't disabled right away, so that a subsequence
+ * vga_get() on the same card will succeed immediately. Resources have a
+ * counter, so locks are only released if the counter reaches 0.
+ */
+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);
+
+/*
+ * Rules for using a bridge to control a VGA descendant decoding: if a bridge
+ * has only one VGA descendant then it can be used to control the VGA routing
+ * for that device. It should always use the bridge closest to the device to
+ * control it. If a bridge has a direct VGA descendant, but also have a sub-
+ * bridge VGA descendant then we cannot use that bridge to control the direct
+ * VGA descendant. So for every device we register, we need to iterate all
+ * its parent bridges so we can invalidate any devices using them properly.
+ */
+static void vga_arbiter_check_bridge_sharing(struct vga_device *vgadev)
+{
+	struct vga_device *same_bridge_vgadev;
+	struct pci_bus *new_bus, *bus;
+	struct pci_dev *new_bridge, *bridge;
+
+	vgadev->bridge_has_one_vga = true;
+
+	if (list_empty(&vga_list))
+		return;
+
+	/* okay iterate the new devices bridge hierarachy */
+	new_bus = vgadev->pdev->bus;
+	while (new_bus) {
+		new_bridge = new_bus->self;
+
+		/* go through list of devices already registered */
+		list_for_each_entry(same_bridge_vgadev, &vga_list, list) {
+			bus = same_bridge_vgadev->pdev->bus;
+			bridge = bus->self;
+
+			/* see if the share a bridge with this device */
+			if (new_bridge == bridge) {
+				/*
+				 * If their direct parent bridge is the same
+				 * as any bridge of this device then it can't
+				 * be used for that device.
+				 */
+				same_bridge_vgadev->bridge_has_one_vga = false;
+			}
+
+			/*
+			 * Now iterate the previous devices bridge hierarchy.
+			 * If the new devices parent bridge is in the other
+			 * devices hierarchy then we can't use it to control
+			 * this device
+			 */
+			while (bus) {
+				bridge = bus->self;
+
+				if (bridge && bridge == vgadev->pdev->bus->self)
+					vgadev->bridge_has_one_vga = false;
+
+				bus = bus->parent;
+			}
+		}
+		new_bus = new_bus->parent;
+	}
+}
+
+/*
+ * 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 = kzalloc(sizeof(struct vga_device), GFP_KERNEL);
+	if (vgadev == NULL) {
+		vgaarb_err(&pdev->dev, "failed to allocate VGA arbiter data\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;
+	}
+
+	/* 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
+	 */
+	if (vga_default == NULL &&
+	    ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)) {
+		vgaarb_info(&pdev->dev, "setting as boot VGA device\n");
+		vga_set_default_device(pdev);
+	}
+
+	vga_arbiter_check_bridge_sharing(vgadev);
+
+	/* Add to the list */
+	list_add_tail(&vgadev->list, &vga_list);
+	vga_count++;
+	vgaarb_info(&pdev->dev, "VGA device added: decodes=%s,owns=%s,locks=%s\n",
+		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)
+		vga_set_default_device(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)
+{
+	struct device *dev = &vgadev->pdev->dev;
+	int old_decodes, decodes_removed, decodes_unlocked;
+
+	old_decodes = vgadev->decodes;
+	decodes_removed = ~new_decodes & old_decodes;
+	decodes_unlocked = vgadev->locks & decodes_removed;
+	vgadev->decodes = new_decodes;
+
+	vgaarb_info(dev, "changed VGA decodes: olddecodes=%s,decodes=%s:owns=%s\n",
+		vga_iostate_to_str(old_decodes),
+		vga_iostate_to_str(vgadev->decodes),
+		vga_iostate_to_str(vgadev->owns));
+
+	/* if we removed locked decodes, lock count goes to zero, and release */
+	if (decodes_unlocked) {
+		if (decodes_unlocked & VGA_RSRC_LEGACY_IO)
+			vgadev->io_lock_cnt = 0;
+		if (decodes_unlocked & VGA_RSRC_LEGACY_MEM)
+			vgadev->mem_lock_cnt = 0;
+		__vga_put(vgadev, decodes_unlocked);
+	}
+
+	/* change decodes counter */
+	if (old_decodes & VGA_RSRC_LEGACY_MASK &&
+	    !(new_decodes & VGA_RSRC_LEGACY_MASK))
+		vga_decode_count--;
+	if (!(old_decodes & VGA_RSRC_LEGACY_MASK) &&
+	    new_decodes & VGA_RSRC_LEGACY_MASK)
+		vga_decode_count++;
+	vgaarb_dbg(dev, "decoding count now is: %d\n", vga_decode_count);
+}
+
+static 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_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);
+}
+
+/**
+ * vga_set_legacy_decoding
+ * @pdev: pci device of the VGA card
+ * @decodes: bit mask of what legacy regions the card decodes
+ *
+ * Indicates to the arbiter if the card decodes legacy VGA IOs, legacy VGA
+ * Memory, both, or none. All cards default to both, the card driver (fbdev for
+ * example) should tell the arbiter if it has disabled legacy decoding, so the
+ * card can be left out of the arbitration process (and can be safe to take
+ * interrupts at any time.
+ */
+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);
+
+/**
+ * vga_client_register - register or unregister a VGA arbitration client
+ * @pdev: pci device of the VGA client
+ * @set_decode: vga decode change callback
+ *
+ * Clients have two callback mechanisms they can use.
+ *
+ * @set_decode callback: If a client can disable its GPU VGA resource, it
+ * will get a callback from this to set the encode/decode state.
+ *
+ * Rationale: we cannot disable VGA decode resources unconditionally some single
+ * GPU laptops seem to require ACPI or BIOS access to the VGA registers to
+ * control things like backlights etc.  Hopefully newer multi-GPU laptops do
+ * something saner, and desktops won't have any special ACPI for this. The
+ * driver will get a callback when VGA arbitration is first used by userspace
+ * since some older X servers have issues.
+ *
+ * This function does not check whether a client for @pdev has been registered
+ * already.
+ *
+ * To unregister just call vga_client_unregister().
+ *
+ * Returns: 0 on success, -1 on failure
+ */
+int vga_client_register(struct pci_dev *pdev,
+		unsigned int (*set_decode)(struct pci_dev *pdev, bool decode))
+{
+	int ret = -ENODEV;
+	struct vga_device *vgadev;
+	unsigned long flags;
+
+	spin_lock_irqsave(&vga_lock, flags);
+	vgadev = vgadev_find(pdev);
+	if (!vgadev)
+		goto bail;
+
+	vgadev->set_decode = set_decode;
+	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         CONFIG_VGA_ARB_MAX_GPUS
+#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 targeting 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[64], *curr_pos;
+	size_t remaining = count;
+
+	int ret_val;
+	int i;
+
+	if (count >= sizeof(kbuf))
+		return -EINVAL;
+	if (copy_from_user(kbuf, buf, count))
+		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_debug("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_debug("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) {
+			ret_val = -EINVAL;
+			goto done;
+		}
+
+		if (io_state & VGA_RSRC_LEGACY_IO && uc->io_cnt == 0) {
+			ret_val = -EINVAL;
+			goto done;
+		}
+
+		if (io_state & VGA_RSRC_LEGACY_MEM && uc->mem_cnt == 0) {
+			ret_val = -EINVAL;
+			goto done;
+		}
+
+		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_debug("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_debug("client 0x%p called 'target'\n", priv);
+		/* if target is default */
+		if (!strncmp(curr_pos, "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_domain_bus_and_slot(domain, bus, devfn);
+			if (!pdev) {
+				pr_debug("invalid PCI address %04x:%02x:%02x.%x\n",
+					 domain, bus, PCI_SLOT(devfn),
+					 PCI_FUNC(devfn));
+				ret_val = -ENODEV;
+				goto done;
+			}
+
+			pr_debug("%s ==> %04x:%02x:%02x.%x pdev %p\n", curr_pos,
+				domain, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
+				pdev);
+		}
+
+		vgadev = vgadev_find(pdev);
+		pr_debug("vgadev %p\n", vgadev);
+		if (vgadev == NULL) {
+			if (pdev) {
+				vgaarb_dbg(&pdev->dev, "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) {
+			vgaarb_dbg(&pdev->dev, "maximum user cards (%d) number reached, ignoring this one!\n",
+				MAX_USER_CARDS);
+			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_debug("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! */
+	return -EPROTO;
+
+done:
+	return ret_val;
+}
+
+static __poll_t vga_arb_fpoll(struct file *file, poll_table *wait)
+{
+	pr_debug("%s\n", __func__);
+
+	poll_wait(file, &vga_wait_queue, wait);
+	return EPOLLIN;
+}
+
+static int vga_arb_open(struct inode *inode, struct file *file)
+{
+	struct vga_arb_private *priv;
+	unsigned long flags;
+
+	pr_debug("%s\n", __func__);
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (priv == NULL)
+		return -ENOMEM;
+	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_debug("%s\n", __func__);
+
+	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;
+		vgaarb_dbg(&uc->pdev->dev, "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_decode) {
+			new_decodes = vgadev->set_decode(vgadev->pdev,
+							 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;
+
+	vgaarb_dbg(dev, "%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,
+	.llseek = noop_llseek,
+};
+
+static struct miscdevice vga_arb_device = {
+	MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
+};
+
+#if defined(CONFIG_ACPI)
+static bool vga_arb_integrated_gpu(struct device *dev)
+{
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+
+	return adev && !strcmp(acpi_device_hid(adev), ACPI_VIDEO_HID);
+}
+#else
+static bool vga_arb_integrated_gpu(struct device *dev)
+{
+	return false;
+}
+#endif
+
+static void __init vga_arb_select_default_device(void)
+{
+	struct pci_dev *pdev, *found = NULL;
+	struct vga_device *vgadev;
+
+#if defined(CONFIG_X86) || defined(CONFIG_IA64)
+	u64 base = screen_info.lfb_base;
+	u64 size = screen_info.lfb_size;
+	u64 limit;
+	resource_size_t start, end;
+	unsigned long flags;
+	int i;
+
+	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		base |= (u64)screen_info.ext_lfb_base << 32;
+
+	limit = base + size;
+
+	list_for_each_entry(vgadev, &vga_list, list) {
+		struct device *dev = &vgadev->pdev->dev;
+		/*
+		 * Override vga_arbiter_add_pci_device()'s I/O based detection
+		 * as it may take the wrong device (e.g. on Apple system under
+		 * EFI).
+		 *
+		 * Select the device owning the boot framebuffer if there is
+		 * one.
+		 */
+
+		/* Does firmware framebuffer belong to us? */
+		for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
+			flags = pci_resource_flags(vgadev->pdev, i);
+
+			if ((flags & IORESOURCE_MEM) == 0)
+				continue;
+
+			start = pci_resource_start(vgadev->pdev, i);
+			end  = pci_resource_end(vgadev->pdev, i);
+
+			if (!start || !end)
+				continue;
+
+			if (base < start || limit >= end)
+				continue;
+
+			if (!vga_default_device())
+				vgaarb_info(dev, "setting as boot device\n");
+			else if (vgadev->pdev != vga_default_device())
+				vgaarb_info(dev, "overriding boot device\n");
+			vga_set_default_device(vgadev->pdev);
+		}
+	}
+#endif
+
+	if (!vga_default_device()) {
+		list_for_each_entry_reverse(vgadev, &vga_list, list) {
+			struct device *dev = &vgadev->pdev->dev;
+			u16 cmd;
+
+			pdev = vgadev->pdev;
+			pci_read_config_word(pdev, PCI_COMMAND, &cmd);
+			if (cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) {
+				found = pdev;
+				if (vga_arb_integrated_gpu(dev))
+					break;
+			}
+		}
+	}
+
+	if (found) {
+		vgaarb_info(&found->dev, "setting as boot device (VGA legacy resources not available)\n");
+		vga_set_default_device(found);
+		return;
+	}
+
+	if (!vga_default_device()) {
+		vgadev = list_first_entry_or_null(&vga_list,
+						  struct vga_device, list);
+		if (vgadev) {
+			struct device *dev = &vgadev->pdev->dev;
+			vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
+			vga_set_default_device(vgadev->pdev);
+		}
+	}
+}
+
+static int __init vga_arb_device_init(void)
+{
+	int rc;
+	struct pci_dev *pdev;
+	struct vga_device *vgadev;
+
+	rc = misc_register(&vga_arb_device);
+	if (rc < 0)
+		pr_err("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);
+
+	list_for_each_entry(vgadev, &vga_list, list) {
+		struct device *dev = &vgadev->pdev->dev;
+
+		if (vgadev->bridge_has_one_vga)
+			vgaarb_info(dev, "bridge control possible\n");
+		else
+			vgaarb_info(dev, "no bridge control possible\n");
+	}
+
+	vga_arb_select_default_device();
+
+	pr_info("loaded\n");
+	return rc;
+}
+subsys_initcall_sync(vga_arb_device_init);