/*
   * Copyright (C) 2007-2008 Advanced Micro Devices, Inc.
   * Author: Joerg Roedel <jroedel@suse.de>
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 as published
   * by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
   */
  
  #define pr_fmt(fmt)    "iommu: " fmt
  
  #include <linux/device.h>
  #include <linux/kernel.h>
  #include <linux/bug.h>
  #include <linux/types.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/errno.h>
  #include <linux/iommu.h>
  #include <linux/idr.h>
  #include <linux/notifier.h>
  #include <linux/err.h>
  #include <linux/pci.h>
  #include <linux/bitops.h>
  #include <trace/events/iommu.h>
  
  static struct kset *iommu_group_kset;
  static struct ida iommu_group_ida;
  static struct mutex iommu_group_mutex;
  
  struct iommu_callback_data {
  	const struct iommu_ops *ops;
  };
  
  struct iommu_group {
  	struct kobject kobj;
  	struct kobject *devices_kobj;
  	struct list_head devices;
  	struct mutex mutex;
  	struct blocking_notifier_head notifier;
  	void *iommu_data;
  	void (*iommu_data_release)(void *iommu_data);
  	char *name;
  	int id;
  	struct iommu_domain *default_domain;
  	struct iommu_domain *domain;
  };
  
  struct iommu_device {
  	struct list_head list;
  	struct device *dev;
  	char *name;
  };
  
  struct iommu_group_attribute {
  	struct attribute attr;
  	ssize_t (*show)(struct iommu_group *group, char *buf);
  	ssize_t (*store)(struct iommu_group *group,
  			 const char *buf, size_t count);
  };
  
  #define IOMMU_GROUP_ATTR(_name, _mode, _show, _store)		\
  struct iommu_group_attribute iommu_group_attr_##_name =		\
  	__ATTR(_name, _mode, _show, _store)
  
  #define to_iommu_group_attr(_attr)	\
  	container_of(_attr, struct iommu_group_attribute, attr)
  #define to_iommu_group(_kobj)		\
  	container_of(_kobj, struct iommu_group, kobj)
  
  static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
  						 unsigned type);
  static int __iommu_attach_device(struct iommu_domain *domain,
  				 struct device *dev);
  static int __iommu_attach_group(struct iommu_domain *domain,
  				struct iommu_group *group);
  static void __iommu_detach_group(struct iommu_domain *domain,
  				 struct iommu_group *group);
  
  static ssize_t iommu_group_attr_show(struct kobject *kobj,
  				     struct attribute *__attr, char *buf)
  {
  	struct iommu_group_attribute *attr = to_iommu_group_attr(__attr);
  	struct iommu_group *group = to_iommu_group(kobj);
  	ssize_t ret = -EIO;
  
  	if (attr->show)
  		ret = attr->show(group, buf);
  	return ret;
  }
  
  static ssize_t iommu_group_attr_store(struct kobject *kobj,
  				      struct attribute *__attr,
  				      const char *buf, size_t count)
  {
  	struct iommu_group_attribute *attr = to_iommu_group_attr(__attr);
  	struct iommu_group *group = to_iommu_group(kobj);
  	ssize_t ret = -EIO;
  
  	if (attr->store)
  		ret = attr->store(group, buf, count);
  	return ret;
  }
  
  static const struct sysfs_ops iommu_group_sysfs_ops = {
  	.show = iommu_group_attr_show,
  	.store = iommu_group_attr_store,
  };
  
  static int iommu_group_create_file(struct iommu_group *group,
  				   struct iommu_group_attribute *attr)
  {
  	return sysfs_create_file(&group->kobj, &attr->attr);
  }
  
  static void iommu_group_remove_file(struct iommu_group *group,
  				    struct iommu_group_attribute *attr)
  {
  	sysfs_remove_file(&group->kobj, &attr->attr);
  }
  
  static ssize_t iommu_group_show_name(struct iommu_group *group, char *buf)
  {
  	return sprintf(buf, "%s
  ", group->name);
  }
  
  static IOMMU_GROUP_ATTR(name, S_IRUGO, iommu_group_show_name, NULL);
  
  static void iommu_group_release(struct kobject *kobj)
  {
  	struct iommu_group *group = to_iommu_group(kobj);
  
  	pr_debug("Releasing group %d
  ", group->id);
  
  	if (group->iommu_data_release)
  		group->iommu_data_release(group->iommu_data);
  
  	mutex_lock(&iommu_group_mutex);
  	ida_remove(&iommu_group_ida, group->id);
  	mutex_unlock(&iommu_group_mutex);
  
  	if (group->default_domain)
  		iommu_domain_free(group->default_domain);
  
  	kfree(group->name);
  	kfree(group);
  }
  
  static struct kobj_type iommu_group_ktype = {
  	.sysfs_ops = &iommu_group_sysfs_ops,
  	.release = iommu_group_release,
  };
  
  /**
   * iommu_group_alloc - Allocate a new group
   * @name: Optional name to associate with group, visible in sysfs
   *
   * This function is called by an iommu driver to allocate a new iommu
   * group.  The iommu group represents the minimum granularity of the iommu.
   * Upon successful return, the caller holds a reference to the supplied
   * group in order to hold the group until devices are added.  Use
   * iommu_group_put() to release this extra reference count, allowing the
   * group to be automatically reclaimed once it has no devices or external
   * references.
   */
  struct iommu_group *iommu_group_alloc(void)
  {
  	struct iommu_group *group;
  	int ret;
  
  	group = kzalloc(sizeof(*group), GFP_KERNEL);
  	if (!group)
  		return ERR_PTR(-ENOMEM);
  
  	group->kobj.kset = iommu_group_kset;
  	mutex_init(&group->mutex);
  	INIT_LIST_HEAD(&group->devices);
  	BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
  
  	mutex_lock(&iommu_group_mutex);
  
  again:
  	if (unlikely(0 == ida_pre_get(&iommu_group_ida, GFP_KERNEL))) {
  		kfree(group);
  		mutex_unlock(&iommu_group_mutex);
  		return ERR_PTR(-ENOMEM);
  	}
  
  	if (-EAGAIN == ida_get_new(&iommu_group_ida, &group->id))
  		goto again;
  
  	mutex_unlock(&iommu_group_mutex);
  
  	ret = kobject_init_and_add(&group->kobj, &iommu_group_ktype,
  				   NULL, "%d", group->id);
  	if (ret) {
  		mutex_lock(&iommu_group_mutex);
  		ida_remove(&iommu_group_ida, group->id);
  		mutex_unlock(&iommu_group_mutex);
  		kfree(group);
  		return ERR_PTR(ret);
  	}
  
  	group->devices_kobj = kobject_create_and_add("devices", &group->kobj);
  	if (!group->devices_kobj) {
  		kobject_put(&group->kobj); /* triggers .release & free */
  		return ERR_PTR(-ENOMEM);
  	}
  
  	/*
  	 * The devices_kobj holds a reference on the group kobject, so
  	 * as long as that exists so will the group.  We can therefore
  	 * use the devices_kobj for reference counting.
  	 */
  	kobject_put(&group->kobj);
  
  	pr_debug("Allocated group %d
  ", group->id);
  
  	return group;
  }
  EXPORT_SYMBOL_GPL(iommu_group_alloc);
  
  struct iommu_group *iommu_group_get_by_id(int id)
  {
  	struct kobject *group_kobj;
  	struct iommu_group *group;
  	const char *name;
  
  	if (!iommu_group_kset)
  		return NULL;
  
  	name = kasprintf(GFP_KERNEL, "%d", id);
  	if (!name)
  		return NULL;
  
  	group_kobj = kset_find_obj(iommu_group_kset, name);
  	kfree(name);
  
  	if (!group_kobj)
  		return NULL;
  
  	group = container_of(group_kobj, struct iommu_group, kobj);
  	BUG_ON(group->id != id);
  
  	kobject_get(group->devices_kobj);
  	kobject_put(&group->kobj);
  
  	return group;
  }
  EXPORT_SYMBOL_GPL(iommu_group_get_by_id);
  
  /**
   * iommu_group_get_iommudata - retrieve iommu_data registered for a group
   * @group: the group
   *
   * iommu drivers can store data in the group for use when doing iommu
   * operations.  This function provides a way to retrieve it.  Caller
   * should hold a group reference.
   */
  void *iommu_group_get_iommudata(struct iommu_group *group)
  {
  	return group->iommu_data;
  }
  EXPORT_SYMBOL_GPL(iommu_group_get_iommudata);
  
  /**
   * iommu_group_set_iommudata - set iommu_data for a group
   * @group: the group
   * @iommu_data: new data
   * @release: release function for iommu_data
   *
   * iommu drivers can store data in the group for use when doing iommu
   * operations.  This function provides a way to set the data after
   * the group has been allocated.  Caller should hold a group reference.
   */
  void iommu_group_set_iommudata(struct iommu_group *group, void *iommu_data,
  			       void (*release)(void *iommu_data))
  {
  	group->iommu_data = iommu_data;
  	group->iommu_data_release = release;
  }
  EXPORT_SYMBOL_GPL(iommu_group_set_iommudata);
  
  /**
   * iommu_group_set_name - set name for a group
   * @group: the group
   * @name: name
   *
   * Allow iommu driver to set a name for a group.  When set it will
   * appear in a name attribute file under the group in sysfs.
   */
  int iommu_group_set_name(struct iommu_group *group, const char *name)
  {
  	int ret;
  
  	if (group->name) {
  		iommu_group_remove_file(group, &iommu_group_attr_name);
  		kfree(group->name);
  		group->name = NULL;
  		if (!name)
  			return 0;
  	}
  
  	group->name = kstrdup(name, GFP_KERNEL);
  	if (!group->name)
  		return -ENOMEM;
  
  	ret = iommu_group_create_file(group, &iommu_group_attr_name);
  	if (ret) {
  		kfree(group->name);
  		group->name = NULL;
  		return ret;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(iommu_group_set_name);
  
  static int iommu_group_create_direct_mappings(struct iommu_group *group,
  					      struct device *dev)
  {
  	struct iommu_domain *domain = group->default_domain;
  	struct iommu_dm_region *entry;
  	struct list_head mappings;
  	unsigned long pg_size;
  	int ret = 0;
  
  	if (!domain || domain->type != IOMMU_DOMAIN_DMA)
  		return 0;
  
  	BUG_ON(!domain->ops->pgsize_bitmap);
  
  	pg_size = 1UL << __ffs(domain->ops->pgsize_bitmap);
  	INIT_LIST_HEAD(&mappings);
  
  	iommu_get_dm_regions(dev, &mappings);
  
  	/* We need to consider overlapping regions for different devices */
  	list_for_each_entry(entry, &mappings, list) {
  		dma_addr_t start, end, addr;
  
  		start = ALIGN(entry->start, pg_size);
  		end   = ALIGN(entry->start + entry->length, pg_size);
  
  		for (addr = start; addr < end; addr += pg_size) {
  			phys_addr_t phys_addr;
  
  			phys_addr = iommu_iova_to_phys(domain, addr);
  			if (phys_addr)
  				continue;
  
  			ret = iommu_map(domain, addr, addr, pg_size, entry->prot);
  			if (ret)
  				goto out;
  		}
  
  	}
  
  out:
  	iommu_put_dm_regions(dev, &mappings);
  
  	return ret;
  }
  
  /**
   * iommu_group_add_device - add a device to an iommu group
   * @group: the group into which to add the device (reference should be held)
   * @dev: the device
   *
   * This function is called by an iommu driver to add a device into a
   * group.  Adding a device increments the group reference count.
   */
  int iommu_group_add_device(struct iommu_group *group, struct device *dev)
  {
  	int ret, i = 0;
  	struct iommu_device *device;
  
  	device = kzalloc(sizeof(*device), GFP_KERNEL);
  	if (!device)
  		return -ENOMEM;
  
  	device->dev = dev;
  
  	ret = sysfs_create_link(&dev->kobj, &group->kobj, "iommu_group");
  	if (ret) {
  		kfree(device);
  		return ret;
  	}
  
  	device->name = kasprintf(GFP_KERNEL, "%s", kobject_name(&dev->kobj));
  rename:
  	if (!device->name) {
  		sysfs_remove_link(&dev->kobj, "iommu_group");
  		kfree(device);
  		return -ENOMEM;
  	}
  
  	ret = sysfs_create_link_nowarn(group->devices_kobj,
  				       &dev->kobj, device->name);
  	if (ret) {
  		kfree(device->name);
  		if (ret == -EEXIST && i >= 0) {
  			/*
  			 * Account for the slim chance of collision
  			 * and append an instance to the name.
  			 */
  			device->name = kasprintf(GFP_KERNEL, "%s.%d",
  						 kobject_name(&dev->kobj), i++);
  			goto rename;
  		}
  
  		sysfs_remove_link(&dev->kobj, "iommu_group");
  		kfree(device);
  		return ret;
  	}
  
  	kobject_get(group->devices_kobj);
  
  	dev->iommu_group = group;
  
  	iommu_group_create_direct_mappings(group, dev);
  
  	mutex_lock(&group->mutex);
  	list_add_tail(&device->list, &group->devices);
  	if (group->domain)
  		__iommu_attach_device(group->domain, dev);
  	mutex_unlock(&group->mutex);
  
  	/* Notify any listeners about change to group. */
  	blocking_notifier_call_chain(&group->notifier,
  				     IOMMU_GROUP_NOTIFY_ADD_DEVICE, dev);
  
  	trace_add_device_to_group(group->id, dev);
  
  	pr_info("Adding device %s to group %d
  ", dev_name(dev), group->id);
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(iommu_group_add_device);
  
  /**
   * iommu_group_remove_device - remove a device from it's current group
   * @dev: device to be removed
   *
   * This function is called by an iommu driver to remove the device from
   * it's current group.  This decrements the iommu group reference count.
   */
  void iommu_group_remove_device(struct device *dev)
  {
  	struct iommu_group *group = dev->iommu_group;
  	struct iommu_device *tmp_device, *device = NULL;
  
  	pr_info("Removing device %s from group %d
  ", dev_name(dev), group->id);
  
  	/* Pre-notify listeners that a device is being removed. */
  	blocking_notifier_call_chain(&group->notifier,
  				     IOMMU_GROUP_NOTIFY_DEL_DEVICE, dev);
  
  	mutex_lock(&group->mutex);
  	list_for_each_entry(tmp_device, &group->devices, list) {
  		if (tmp_device->dev == dev) {
  			device = tmp_device;
  			list_del(&device->list);
  			break;
  		}
  	}
  	mutex_unlock(&group->mutex);
  
  	if (!device)
  		return;
  
  	sysfs_remove_link(group->devices_kobj, device->name);
  	sysfs_remove_link(&dev->kobj, "iommu_group");
  
  	trace_remove_device_from_group(group->id, dev);
  
  	kfree(device->name);
  	kfree(device);
  	dev->iommu_group = NULL;
  	kobject_put(group->devices_kobj);
  }
  EXPORT_SYMBOL_GPL(iommu_group_remove_device);
  
  static int iommu_group_device_count(struct iommu_group *group)
  {
  	struct iommu_device *entry;
  	int ret = 0;
  
  	list_for_each_entry(entry, &group->devices, list)
  		ret++;
  
  	return ret;
  }
  
  /**
   * iommu_group_for_each_dev - iterate over each device in the group
   * @group: the group
   * @data: caller opaque data to be passed to callback function
   * @fn: caller supplied callback function
   *
   * This function is called by group users to iterate over group devices.
   * Callers should hold a reference count to the group during callback.
   * The group->mutex is held across callbacks, which will block calls to
   * iommu_group_add/remove_device.
   */
  static int __iommu_group_for_each_dev(struct iommu_group *group, void *data,
  				      int (*fn)(struct device *, void *))
  {
  	struct iommu_device *device;
  	int ret = 0;
  
  	list_for_each_entry(device, &group->devices, list) {
  		ret = fn(device->dev, data);
  		if (ret)
  			break;
  	}
  	return ret;
  }
  
  
  int iommu_group_for_each_dev(struct iommu_group *group, void *data,
  			     int (*fn)(struct device *, void *))
  {
  	int ret;
  
  	mutex_lock(&group->mutex);
  	ret = __iommu_group_for_each_dev(group, data, fn);
  	mutex_unlock(&group->mutex);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iommu_group_for_each_dev);
  
  /**
   * iommu_group_get - Return the group for a device and increment reference
   * @dev: get the group that this device belongs to
   *
   * This function is called by iommu drivers and users to get the group
   * for the specified device.  If found, the group is returned and the group
   * reference in incremented, else NULL.
   */
  struct iommu_group *iommu_group_get(struct device *dev)
  {
  	struct iommu_group *group = dev->iommu_group;
  
  	if (group)
  		kobject_get(group->devices_kobj);
  
  	return group;
  }
  EXPORT_SYMBOL_GPL(iommu_group_get);
  
  /**
   * iommu_group_put - Decrement group reference
   * @group: the group to use
   *
   * This function is called by iommu drivers and users to release the
   * iommu group.  Once the reference count is zero, the group is released.
   */
  void iommu_group_put(struct iommu_group *group)
  {
  	if (group)
  		kobject_put(group->devices_kobj);
  }
  EXPORT_SYMBOL_GPL(iommu_group_put);
  
  /**
   * iommu_group_register_notifier - Register a notifier for group changes
   * @group: the group to watch
   * @nb: notifier block to signal
   *
   * This function allows iommu group users to track changes in a group.
   * See include/linux/iommu.h for actions sent via this notifier.  Caller
   * should hold a reference to the group throughout notifier registration.
   */
  int iommu_group_register_notifier(struct iommu_group *group,
  				  struct notifier_block *nb)
  {
  	return blocking_notifier_chain_register(&group->notifier, nb);
  }
  EXPORT_SYMBOL_GPL(iommu_group_register_notifier);
  
  /**
   * iommu_group_unregister_notifier - Unregister a notifier
   * @group: the group to watch
   * @nb: notifier block to signal
   *
   * Unregister a previously registered group notifier block.
   */
  int iommu_group_unregister_notifier(struct iommu_group *group,
  				    struct notifier_block *nb)
  {
  	return blocking_notifier_chain_unregister(&group->notifier, nb);
  }
  EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
  
  /**
   * iommu_group_id - Return ID for a group
   * @group: the group to ID
   *
   * Return the unique ID for the group matching the sysfs group number.
   */
  int iommu_group_id(struct iommu_group *group)
  {
  	return group->id;
  }
  EXPORT_SYMBOL_GPL(iommu_group_id);
  
  static struct iommu_group *get_pci_alias_group(struct pci_dev *pdev,
  					       unsigned long *devfns);
  
  /*
   * To consider a PCI device isolated, we require ACS to support Source
   * Validation, Request Redirection, Completer Redirection, and Upstream
   * Forwarding.  This effectively means that devices cannot spoof their
   * requester ID, requests and completions cannot be redirected, and all
   * transactions are forwarded upstream, even as it passes through a
   * bridge where the target device is downstream.
   */
  #define REQ_ACS_FLAGS   (PCI_ACS_SV | PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF)
  
  /*
   * For multifunction devices which are not isolated from each other, find
   * all the other non-isolated functions and look for existing groups.  For
   * each function, we also need to look for aliases to or from other devices
   * that may already have a group.
   */
  static struct iommu_group *get_pci_function_alias_group(struct pci_dev *pdev,
  							unsigned long *devfns)
  {
  	struct pci_dev *tmp = NULL;
  	struct iommu_group *group;
  
  	if (!pdev->multifunction || pci_acs_enabled(pdev, REQ_ACS_FLAGS))
  		return NULL;
  
  	for_each_pci_dev(tmp) {
  		if (tmp == pdev || tmp->bus != pdev->bus ||
  		    PCI_SLOT(tmp->devfn) != PCI_SLOT(pdev->devfn) ||
  		    pci_acs_enabled(tmp, REQ_ACS_FLAGS))
  			continue;
  
  		group = get_pci_alias_group(tmp, devfns);
  		if (group) {
  			pci_dev_put(tmp);
  			return group;
  		}
  	}
  
  	return NULL;
  }
  
  /*
   * Look for aliases to or from the given device for exisiting groups.  The
   * dma_alias_devfn only supports aliases on the same bus, therefore the search
   * space is quite small (especially since we're really only looking at pcie
   * device, and therefore only expect multiple slots on the root complex or
   * downstream switch ports).  It's conceivable though that a pair of
   * multifunction devices could have aliases between them that would cause a
   * loop.  To prevent this, we use a bitmap to track where we've been.
   */
  static struct iommu_group *get_pci_alias_group(struct pci_dev *pdev,
  					       unsigned long *devfns)
  {
  	struct pci_dev *tmp = NULL;
  	struct iommu_group *group;
  
  	if (test_and_set_bit(pdev->devfn & 0xff, devfns))
  		return NULL;
  
  	group = iommu_group_get(&pdev->dev);
  	if (group)
  		return group;
  
  	for_each_pci_dev(tmp) {
  		if (tmp == pdev || tmp->bus != pdev->bus)
  			continue;
  
  		/* We alias them or they alias us */
  		if (((pdev->dev_flags & PCI_DEV_FLAGS_DMA_ALIAS_DEVFN) &&
  		     pdev->dma_alias_devfn == tmp->devfn) ||
  		    ((tmp->dev_flags & PCI_DEV_FLAGS_DMA_ALIAS_DEVFN) &&
  		     tmp->dma_alias_devfn == pdev->devfn)) {
  
  			group = get_pci_alias_group(tmp, devfns);
  			if (group) {
  				pci_dev_put(tmp);
  				return group;
  			}
  
  			group = get_pci_function_alias_group(tmp, devfns);
  			if (group) {
  				pci_dev_put(tmp);
  				return group;
  			}
  		}
  	}
  
  	return NULL;
  }
  
  struct group_for_pci_data {
  	struct pci_dev *pdev;
  	struct iommu_group *group;
  };
  
  /*
   * DMA alias iterator callback, return the last seen device.  Stop and return
   * the IOMMU group if we find one along the way.
   */
  static int get_pci_alias_or_group(struct pci_dev *pdev, u16 alias, void *opaque)
  {
  	struct group_for_pci_data *data = opaque;
  
  	data->pdev = pdev;
  	data->group = iommu_group_get(&pdev->dev);
  
  	return data->group != NULL;
  }
  
  /*
   * Generic device_group call-back function. It just allocates one
   * iommu-group per device.
   */
  struct iommu_group *generic_device_group(struct device *dev)
  {
  	struct iommu_group *group;
  
  	group = iommu_group_alloc();
  	if (IS_ERR(group))
  		return NULL;
  
  	return group;
  }
  
  /*
   * Use standard PCI bus topology, isolation features, and DMA alias quirks
   * to find or create an IOMMU group for a device.
   */
  struct iommu_group *pci_device_group(struct device *dev)
  {
  	struct pci_dev *pdev = to_pci_dev(dev);
  	struct group_for_pci_data data;
  	struct pci_bus *bus;
  	struct iommu_group *group = NULL;
  	u64 devfns[4] = { 0 };
  
  	if (WARN_ON(!dev_is_pci(dev)))
  		return ERR_PTR(-EINVAL);
  
  	/*
  	 * Find the upstream DMA alias for the device.  A device must not
  	 * be aliased due to topology in order to have its own IOMMU group.
  	 * If we find an alias along the way that already belongs to a
  	 * group, use it.
  	 */
  	if (pci_for_each_dma_alias(pdev, get_pci_alias_or_group, &data))
  		return data.group;
  
  	pdev = data.pdev;
  
  	/*
  	 * Continue upstream from the point of minimum IOMMU granularity
  	 * due to aliases to the point where devices are protected from
  	 * peer-to-peer DMA by PCI ACS.  Again, if we find an existing
  	 * group, use it.
  	 */
  	for (bus = pdev->bus; !pci_is_root_bus(bus); bus = bus->parent) {
  		if (!bus->self)
  			continue;
  
  		if (pci_acs_path_enabled(bus->self, NULL, REQ_ACS_FLAGS))
  			break;
  
  		pdev = bus->self;
  
  		group = iommu_group_get(&pdev->dev);
  		if (group)
  			return group;
  	}
  
  	/*
  	 * Look for existing groups on device aliases.  If we alias another
  	 * device or another device aliases us, use the same group.
  	 */
  	group = get_pci_alias_group(pdev, (unsigned long *)devfns);
  	if (group)
  		return group;
  
  	/*
  	 * Look for existing groups on non-isolated functions on the same
  	 * slot and aliases of those funcions, if any.  No need to clear
  	 * the search bitmap, the tested devfns are still valid.
  	 */
  	group = get_pci_function_alias_group(pdev, (unsigned long *)devfns);
  	if (group)
  		return group;
  
  	/* No shared group found, allocate new */
  	group = iommu_group_alloc();
  	if (IS_ERR(group))
  		return NULL;
  
  	return group;
  }
  
  /**
   * iommu_group_get_for_dev - Find or create the IOMMU group for a device
   * @dev: target device
   *
   * This function is intended to be called by IOMMU drivers and extended to
   * support common, bus-defined algorithms when determining or creating the
   * IOMMU group for a device.  On success, the caller will hold a reference
   * to the returned IOMMU group, which will already include the provided
   * device.  The reference should be released with iommu_group_put().
   */
  struct iommu_group *iommu_group_get_for_dev(struct device *dev)
  {
  	const struct iommu_ops *ops = dev->bus->iommu_ops;
  	struct iommu_group *group;
  	int ret;
  
  	group = iommu_group_get(dev);
  	if (group)
  		return group;
  
  	group = ERR_PTR(-EINVAL);
  
  	if (ops && ops->device_group)
  		group = ops->device_group(dev);
  
  	if (IS_ERR(group))
  		return group;
  
  	/*
  	 * Try to allocate a default domain - needs support from the
  	 * IOMMU driver.
  	 */
  	if (!group->default_domain) {
  		group->default_domain = __iommu_domain_alloc(dev->bus,
  							     IOMMU_DOMAIN_DMA);
  		if (!group->domain)
  			group->domain = group->default_domain;
  	}
  
  	ret = iommu_group_add_device(group, dev);
  	if (ret) {
  		iommu_group_put(group);
  		return ERR_PTR(ret);
  	}
  
  	return group;
  }
  
  struct iommu_domain *iommu_group_default_domain(struct iommu_group *group)
  {
  	return group->default_domain;
  }
  
  static int add_iommu_group(struct device *dev, void *data)
  {
  	struct iommu_callback_data *cb = data;
  	const struct iommu_ops *ops = cb->ops;
  	int ret;
  
  	if (!ops->add_device)
  		return 0;
  
  	WARN_ON(dev->iommu_group);
  
  	ret = ops->add_device(dev);
  
  	/*
  	 * We ignore -ENODEV errors for now, as they just mean that the
  	 * device is not translated by an IOMMU. We still care about
  	 * other errors and fail to initialize when they happen.
  	 */
  	if (ret == -ENODEV)
  		ret = 0;
  
  	return ret;
  }
  
  static int remove_iommu_group(struct device *dev, void *data)
  {
  	struct iommu_callback_data *cb = data;
  	const struct iommu_ops *ops = cb->ops;
  
  	if (ops->remove_device && dev->iommu_group)
  		ops->remove_device(dev);
  
  	return 0;
  }
  
  static int iommu_bus_notifier(struct notifier_block *nb,
  			      unsigned long action, void *data)
  {
  	struct device *dev = data;
  	const struct iommu_ops *ops = dev->bus->iommu_ops;
  	struct iommu_group *group;
  	unsigned long group_action = 0;
  
  	/*
  	 * ADD/DEL call into iommu driver ops if provided, which may
  	 * result in ADD/DEL notifiers to group->notifier
  	 */
  	if (action == BUS_NOTIFY_ADD_DEVICE) {
  		if (ops->add_device)
  			return ops->add_device(dev);
  	} else if (action == BUS_NOTIFY_REMOVED_DEVICE) {
  		if (ops->remove_device && dev->iommu_group) {
  			ops->remove_device(dev);
  			return 0;
  		}
  	}
  
  	/*
  	 * Remaining BUS_NOTIFYs get filtered and republished to the
  	 * group, if anyone is listening
  	 */
  	group = iommu_group_get(dev);
  	if (!group)
  		return 0;
  
  	switch (action) {
  	case BUS_NOTIFY_BIND_DRIVER:
  		group_action = IOMMU_GROUP_NOTIFY_BIND_DRIVER;
  		break;
  	case BUS_NOTIFY_BOUND_DRIVER:
  		group_action = IOMMU_GROUP_NOTIFY_BOUND_DRIVER;
  		break;
  	case BUS_NOTIFY_UNBIND_DRIVER:
  		group_action = IOMMU_GROUP_NOTIFY_UNBIND_DRIVER;
  		break;
  	case BUS_NOTIFY_UNBOUND_DRIVER:
  		group_action = IOMMU_GROUP_NOTIFY_UNBOUND_DRIVER;
  		break;
  	}
  
  	if (group_action)
  		blocking_notifier_call_chain(&group->notifier,
  					     group_action, dev);
  
  	iommu_group_put(group);
  	return 0;
  }
  
  static int iommu_bus_init(struct bus_type *bus, const struct iommu_ops *ops)
  {
  	int err;
  	struct notifier_block *nb;
  	struct iommu_callback_data cb = {
  		.ops = ops,
  	};
  
  	nb = kzalloc(sizeof(struct notifier_block), GFP_KERNEL);
  	if (!nb)
  		return -ENOMEM;
  
  	nb->notifier_call = iommu_bus_notifier;
  
  	err = bus_register_notifier(bus, nb);
  	if (err)
  		goto out_free;
  
  	err = bus_for_each_dev(bus, NULL, &cb, add_iommu_group);
  	if (err)
  		goto out_err;
  
  
  	return 0;
  
  out_err:
  	/* Clean up */
  	bus_for_each_dev(bus, NULL, &cb, remove_iommu_group);
  	bus_unregister_notifier(bus, nb);
  
  out_free:
  	kfree(nb);
  
  	return err;
  }
  
  /**
   * bus_set_iommu - set iommu-callbacks for the bus
   * @bus: bus.
   * @ops: the callbacks provided by the iommu-driver
   *
   * This function is called by an iommu driver to set the iommu methods
   * used for a particular bus. Drivers for devices on that bus can use
   * the iommu-api after these ops are registered.
   * This special function is needed because IOMMUs are usually devices on
   * the bus itself, so the iommu drivers are not initialized when the bus
   * is set up. With this function the iommu-driver can set the iommu-ops
   * afterwards.
   */
  int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops)
  {
  	int err;
  
  	if (bus->iommu_ops != NULL)
  		return -EBUSY;
  
  	bus->iommu_ops = ops;
  
  	/* Do IOMMU specific setup for this bus-type */
  	err = iommu_bus_init(bus, ops);
  	if (err)
  		bus->iommu_ops = NULL;
  
  	return err;
  }
  EXPORT_SYMBOL_GPL(bus_set_iommu);
  
  bool iommu_present(struct bus_type *bus)
  {
  	return bus->iommu_ops != NULL;
  }
  EXPORT_SYMBOL_GPL(iommu_present);
  
  bool iommu_capable(struct bus_type *bus, enum iommu_cap cap)
  {
  	if (!bus->iommu_ops || !bus->iommu_ops->capable)
  		return false;
  
  	return bus->iommu_ops->capable(cap);
  }
  EXPORT_SYMBOL_GPL(iommu_capable);
  
  /**
   * iommu_set_fault_handler() - set a fault handler for an iommu domain
   * @domain: iommu domain
   * @handler: fault handler
   * @token: user data, will be passed back to the fault handler
   *
   * This function should be used by IOMMU users which want to be notified
   * whenever an IOMMU fault happens.
   *
   * The fault handler itself should return 0 on success, and an appropriate
   * error code otherwise.
   */
  void iommu_set_fault_handler(struct iommu_domain *domain,
  					iommu_fault_handler_t handler,
  					void *token)
  {
  	BUG_ON(!domain);
  
  	domain->handler = handler;
  	domain->handler_token = token;
  }
  EXPORT_SYMBOL_GPL(iommu_set_fault_handler);
  
  static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
  						 unsigned type)
  {
  	struct iommu_domain *domain;
  
  	if (bus == NULL || bus->iommu_ops == NULL)
  		return NULL;
  
  	domain = bus->iommu_ops->domain_alloc(type);
  	if (!domain)
  		return NULL;
  
  	domain->ops  = bus->iommu_ops;
  	domain->type = type;
  
  	return domain;
  }
  
  struct iommu_domain *iommu_domain_alloc(struct bus_type *bus)
  {
  	return __iommu_domain_alloc(bus, IOMMU_DOMAIN_UNMANAGED);
  }
  EXPORT_SYMBOL_GPL(iommu_domain_alloc);
  
  void iommu_domain_free(struct iommu_domain *domain)
  {
  	domain->ops->domain_free(domain);
  }
  EXPORT_SYMBOL_GPL(iommu_domain_free);
  
  static int __iommu_attach_device(struct iommu_domain *domain,
  				 struct device *dev)
  {
  	int ret;
  	if (unlikely(domain->ops->attach_dev == NULL))
  		return -ENODEV;
  
  	ret = domain->ops->attach_dev(domain, dev);
  	if (!ret)
  		trace_attach_device_to_domain(dev);
  	return ret;
  }
  
  int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
  {
  	struct iommu_group *group;
  	int ret;
  
  	group = iommu_group_get(dev);
  	/* FIXME: Remove this when groups a mandatory for iommu drivers */
  	if (group == NULL)
  		return __iommu_attach_device(domain, dev);
  
  	/*
  	 * We have a group - lock it to make sure the device-count doesn't
  	 * change while we are attaching
  	 */
  	mutex_lock(&group->mutex);
  	ret = -EINVAL;
  	if (iommu_group_device_count(group) != 1)
  		goto out_unlock;
  
  	ret = __iommu_attach_group(domain, group);
  
  out_unlock:
  	mutex_unlock(&group->mutex);
  	iommu_group_put(group);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iommu_attach_device);
  
  static void __iommu_detach_device(struct iommu_domain *domain,
  				  struct device *dev)
  {
  	if (unlikely(domain->ops->detach_dev == NULL))
  		return;
  
  	domain->ops->detach_dev(domain, dev);
  	trace_detach_device_from_domain(dev);
  }
  
  void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
  {
  	struct iommu_group *group;
  
  	group = iommu_group_get(dev);
  	/* FIXME: Remove this when groups a mandatory for iommu drivers */
  	if (group == NULL)
  		return __iommu_detach_device(domain, dev);
  
  	mutex_lock(&group->mutex);
  	if (iommu_group_device_count(group) != 1) {
  		WARN_ON(1);
  		goto out_unlock;
  	}
  
  	__iommu_detach_group(domain, group);
  
  out_unlock:
  	mutex_unlock(&group->mutex);
  	iommu_group_put(group);
  }
  EXPORT_SYMBOL_GPL(iommu_detach_device);
  
  struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)
  {
  	struct iommu_domain *domain;
  	struct iommu_group *group;
  
  	group = iommu_group_get(dev);
  	/* FIXME: Remove this when groups a mandatory for iommu drivers */
  	if (group == NULL)
  		return NULL;
  
  	domain = group->domain;
  
  	iommu_group_put(group);
  
  	return domain;
  }
  EXPORT_SYMBOL_GPL(iommu_get_domain_for_dev);
  
  /*
   * IOMMU groups are really the natrual working unit of the IOMMU, but
   * the IOMMU API works on domains and devices.  Bridge that gap by
   * iterating over the devices in a group.  Ideally we'd have a single
   * device which represents the requestor ID of the group, but we also
   * allow IOMMU drivers to create policy defined minimum sets, where
   * the physical hardware may be able to distiguish members, but we
   * wish to group them at a higher level (ex. untrusted multi-function
   * PCI devices).  Thus we attach each device.
   */
  static int iommu_group_do_attach_device(struct device *dev, void *data)
  {
  	struct iommu_domain *domain = data;
  
  	return __iommu_attach_device(domain, dev);
  }
  
  static int __iommu_attach_group(struct iommu_domain *domain,
  				struct iommu_group *group)
  {
  	int ret;
  
  	if (group->default_domain && group->domain != group->default_domain)
  		return -EBUSY;
  
  	ret = __iommu_group_for_each_dev(group, domain,
  					 iommu_group_do_attach_device);
  	if (ret == 0)
  		group->domain = domain;
  
  	return ret;
  }
  
  int iommu_attach_group(struct iommu_domain *domain, struct iommu_group *group)
  {
  	int ret;
  
  	mutex_lock(&group->mutex);
  	ret = __iommu_attach_group(domain, group);
  	mutex_unlock(&group->mutex);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iommu_attach_group);
  
  static int iommu_group_do_detach_device(struct device *dev, void *data)
  {
  	struct iommu_domain *domain = data;
  
  	__iommu_detach_device(domain, dev);
  
  	return 0;
  }
  
  static void __iommu_detach_group(struct iommu_domain *domain,
  				 struct iommu_group *group)
  {
  	int ret;
  
  	if (!group->default_domain) {
  		__iommu_group_for_each_dev(group, domain,
  					   iommu_group_do_detach_device);
  		group->domain = NULL;
  		return;
  	}
  
  	if (group->domain == group->default_domain)
  		return;
  
  	/* Detach by re-attaching to the default domain */
  	ret = __iommu_group_for_each_dev(group, group->default_domain,
  					 iommu_group_do_attach_device);
  	if (ret != 0)
  		WARN_ON(1);
  	else
  		group->domain = group->default_domain;
  }
  
  void iommu_detach_group(struct iommu_domain *domain, struct iommu_group *group)
  {
  	mutex_lock(&group->mutex);
  	__iommu_detach_group(domain, group);
  	mutex_unlock(&group->mutex);
  }
  EXPORT_SYMBOL_GPL(iommu_detach_group);
  
  phys_addr_t iommu_iova_to_phys(struct iommu_domain *domain, dma_addr_t iova)
  {
  	if (unlikely(domain->ops->iova_to_phys == NULL))
  		return 0;
  
  	return domain->ops->iova_to_phys(domain, iova);
  }
  EXPORT_SYMBOL_GPL(iommu_iova_to_phys);
  
  static size_t iommu_pgsize(struct iommu_domain *domain,
  			   unsigned long addr_merge, size_t size)
  {
  	unsigned int pgsize_idx;
  	size_t pgsize;
  
  	/* Max page size that still fits into 'size' */
  	pgsize_idx = __fls(size);
  
  	/* need to consider alignment requirements ? */
  	if (likely(addr_merge)) {
  		/* Max page size allowed by address */
  		unsigned int align_pgsize_idx = __ffs(addr_merge);
  		pgsize_idx = min(pgsize_idx, align_pgsize_idx);
  	}
  
  	/* build a mask of acceptable page sizes */
  	pgsize = (1UL << (pgsize_idx + 1)) - 1;
  
  	/* throw away page sizes not supported by the hardware */
  	pgsize &= domain->ops->pgsize_bitmap;
  
  	/* make sure we're still sane */
  	BUG_ON(!pgsize);
  
  	/* pick the biggest page */
  	pgsize_idx = __fls(pgsize);
  	pgsize = 1UL << pgsize_idx;
  
  	return pgsize;
  }
  
  int iommu_map(struct iommu_domain *domain, unsigned long iova,
  	      phys_addr_t paddr, size_t size, int prot)
  {
  	unsigned long orig_iova = iova;
  	unsigned int min_pagesz;
  	size_t orig_size = size;
  	int ret = 0;
  
  	if (unlikely(domain->ops->map == NULL ||
  		     domain->ops->pgsize_bitmap == 0UL))
  		return -ENODEV;
  
  	if (unlikely(!(domain->type & __IOMMU_DOMAIN_PAGING)))
  		return -EINVAL;
  
  	/* find out the minimum page size supported */
  	min_pagesz = 1 << __ffs(domain->ops->pgsize_bitmap);
  
  	/*
  	 * both the virtual address and the physical one, as well as
  	 * the size of the mapping, must be aligned (at least) to the
  	 * size of the smallest page supported by the hardware
  	 */
  	if (!IS_ALIGNED(iova | paddr | size, min_pagesz)) {
  		pr_err("unaligned: iova 0x%lx pa %pa size 0x%zx min_pagesz 0x%x
  ",
  		       iova, &paddr, size, min_pagesz);
  		return -EINVAL;
  	}
  
  	pr_debug("map: iova 0x%lx pa %pa size 0x%zx
  ", iova, &paddr, size);
  
  	while (size) {
  		size_t pgsize = iommu_pgsize(domain, iova | paddr, size);
  
  		pr_debug("mapping: iova 0x%lx pa %pa pgsize 0x%zx
  ",
  			 iova, &paddr, pgsize);
  
  		ret = domain->ops->map(domain, iova, paddr, pgsize, prot);
  		if (ret)
  			break;
  
  		iova += pgsize;
  		paddr += pgsize;
  		size -= pgsize;
  	}
  
  	/* unroll mapping in case something went wrong */
  	if (ret)
  		iommu_unmap(domain, orig_iova, orig_size - size);
  	else
  		trace_map(orig_iova, paddr, orig_size);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iommu_map);
  
  size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
  {
  	size_t unmapped_page, unmapped = 0;
  	unsigned int min_pagesz;
  	unsigned long orig_iova = iova;
  
  	if (unlikely(domain->ops->unmap == NULL ||
  		     domain->ops->pgsize_bitmap == 0UL))
  		return -ENODEV;
  
  	if (unlikely(!(domain->type & __IOMMU_DOMAIN_PAGING)))
  		return -EINVAL;
  
  	/* find out the minimum page size supported */
  	min_pagesz = 1 << __ffs(domain->ops->pgsize_bitmap);
  
  	/*
  	 * The virtual address, as well as the size of the mapping, must be
  	 * aligned (at least) to the size of the smallest page supported
  	 * by the hardware
  	 */
  	if (!IS_ALIGNED(iova | size, min_pagesz)) {
  		pr_err("unaligned: iova 0x%lx size 0x%zx min_pagesz 0x%x
  ",
  		       iova, size, min_pagesz);
  		return -EINVAL;
  	}
  
  	pr_debug("unmap this: iova 0x%lx size 0x%zx
  ", iova, size);
  
  	/*
  	 * Keep iterating until we either unmap 'size' bytes (or more)
  	 * or we hit an area that isn't mapped.
  	 */
  	while (unmapped < size) {
  		size_t pgsize = iommu_pgsize(domain, iova, size - unmapped);
  
  		unmapped_page = domain->ops->unmap(domain, iova, pgsize);
  		if (!unmapped_page)
  			break;
  
  		pr_debug("unmapped: iova 0x%lx size 0x%zx
  ",
  			 iova, unmapped_page);
  
  		iova += unmapped_page;
  		unmapped += unmapped_page;
  	}
  
  	trace_unmap(orig_iova, size, unmapped);
  	return unmapped;
  }
  EXPORT_SYMBOL_GPL(iommu_unmap);
  
  size_t default_iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
  			 struct scatterlist *sg, unsigned int nents, int prot)
  {
  	struct scatterlist *s;
  	size_t mapped = 0;
  	unsigned int i, min_pagesz;
  	int ret;
  
  	if (unlikely(domain->ops->pgsize_bitmap == 0UL))
  		return 0;
  
  	min_pagesz = 1 << __ffs(domain->ops->pgsize_bitmap);
  
  	for_each_sg(sg, s, nents, i) {
  		phys_addr_t phys = page_to_phys(sg_page(s)) + s->offset;
  
  		/*
  		 * We are mapping on IOMMU page boundaries, so offset within
  		 * the page must be 0. However, the IOMMU may support pages
  		 * smaller than PAGE_SIZE, so s->offset may still represent
  		 * an offset of that boundary within the CPU page.
  		 */
  		if (!IS_ALIGNED(s->offset, min_pagesz))
  			goto out_err;
  
  		ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
  		if (ret)
  			goto out_err;
  
  		mapped += s->length;
  	}
  
  	return mapped;
  
  out_err:
  	/* undo mappings already done */
  	iommu_unmap(domain, iova, mapped);
  
  	return 0;
  
  }
  EXPORT_SYMBOL_GPL(default_iommu_map_sg);
  
  int iommu_domain_window_enable(struct iommu_domain *domain, u32 wnd_nr,
  			       phys_addr_t paddr, u64 size, int prot)
  {
  	if (unlikely(domain->ops->domain_window_enable == NULL))
  		return -ENODEV;
  
  	return domain->ops->domain_window_enable(domain, wnd_nr, paddr, size,
  						 prot);
  }
  EXPORT_SYMBOL_GPL(iommu_domain_window_enable);
  
  void iommu_domain_window_disable(struct iommu_domain *domain, u32 wnd_nr)
  {
  	if (unlikely(domain->ops->domain_window_disable == NULL))
  		return;
  
  	return domain->ops->domain_window_disable(domain, wnd_nr);
  }
  EXPORT_SYMBOL_GPL(iommu_domain_window_disable);
  
  static int __init iommu_init(void)
  {
  	iommu_group_kset = kset_create_and_add("iommu_groups",
  					       NULL, kernel_kobj);
  	ida_init(&iommu_group_ida);
  	mutex_init(&iommu_group_mutex);
  
  	BUG_ON(!iommu_group_kset);
  
  	return 0;
  }
  core_initcall(iommu_init);
  
  int iommu_domain_get_attr(struct iommu_domain *domain,
  			  enum iommu_attr attr, void *data)
  {
  	struct iommu_domain_geometry *geometry;
  	bool *paging;
  	int ret = 0;
  	u32 *count;
  
  	switch (attr) {
  	case DOMAIN_ATTR_GEOMETRY:
  		geometry  = data;
  		*geometry = domain->geometry;
  
  		break;
  	case DOMAIN_ATTR_PAGING:
  		paging  = data;
  		*paging = (domain->ops->pgsize_bitmap != 0UL);
  		break;
  	case DOMAIN_ATTR_WINDOWS:
  		count = data;
  
  		if (domain->ops->domain_get_windows != NULL)
  			*count = domain->ops->domain_get_windows(domain);
  		else
  			ret = -ENODEV;
  
  		break;
  	default:
  		if (!domain->ops->domain_get_attr)
  			return -EINVAL;
  
  		ret = domain->ops->domain_get_attr(domain, attr, data);
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iommu_domain_get_attr);
  
  int iommu_domain_set_attr(struct iommu_domain *domain,
  			  enum iommu_attr attr, void *data)
  {
  	int ret = 0;
  	u32 *count;
  
  	switch (attr) {
  	case DOMAIN_ATTR_WINDOWS:
  		count = data;
  
  		if (domain->ops->domain_set_windows != NULL)
  			ret = domain->ops->domain_set_windows(domain, *count);
  		else
  			ret = -ENODEV;
  
  		break;
  	default:
  		if (domain->ops->domain_set_attr == NULL)
  			return -EINVAL;
  
  		ret = domain->ops->domain_set_attr(domain, attr, data);
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(iommu_domain_set_attr);
  
  void iommu_get_dm_regions(struct device *dev, struct list_head *list)
  {
  	const struct iommu_ops *ops = dev->bus->iommu_ops;
  
  	if (ops && ops->get_dm_regions)
  		ops->get_dm_regions(dev, list);
  }
  
  void iommu_put_dm_regions(struct device *dev, struct list_head *list)
  {
  	const struct iommu_ops *ops = dev->bus->iommu_ops;
  
  	if (ops && ops->put_dm_regions)
  		ops->put_dm_regions(dev, list);
  }
  
  /* Request that a device is direct mapped by the IOMMU */
  int iommu_request_dm_for_dev(struct device *dev)
  {
  	struct iommu_domain *dm_domain;
  	struct iommu_group *group;
  	int ret;
  
  	/* Device must already be in a group before calling this function */
  	group = iommu_group_get_for_dev(dev);
  	if (IS_ERR(group))
  		return PTR_ERR(group);
  
  	mutex_lock(&group->mutex);
  
  	/* Check if the default domain is already direct mapped */
  	ret = 0;
  	if (group->default_domain &&
  	    group->default_domain->type == IOMMU_DOMAIN_IDENTITY)
  		goto out;
  
  	/* Don't change mappings of existing devices */
  	ret = -EBUSY;
  	if (iommu_group_device_count(group) != 1)
  		goto out;
  
  	/* Allocate a direct mapped domain */
  	ret = -ENOMEM;
  	dm_domain = __iommu_domain_alloc(dev->bus, IOMMU_DOMAIN_IDENTITY);
  	if (!dm_domain)
  		goto out;
  
  	/* Attach the device to the domain */
  	ret = __iommu_attach_group(dm_domain, group);
  	if (ret) {
  		iommu_domain_free(dm_domain);
  		goto out;
  	}
  
  	/* Make the direct mapped domain the default for this group */
  	if (group->default_domain)
  		iommu_domain_free(group->default_domain);
  	group->default_domain = dm_domain;
  
  	pr_info("Using direct mapping for device %s
  ", dev_name(dev));
  
  	ret = 0;
  out:
  	mutex_unlock(&group->mutex);
  	iommu_group_put(group);
  
  	return ret;
  }