text: // SPDX-License-Identifier: GPL-2.0
  /*
   * PCI Peer 2 Peer DMA support.
   *
   * Copyright (c) 2016-2018, Logan Gunthorpe
   * Copyright (c) 2016-2017, Microsemi Corporation
   * Copyright (c) 2017, Christoph Hellwig
   * Copyright (c) 2018, Eideticom Inc.
   */
  
  #define pr_fmt(fmt) "pci-p2pdma: " fmt
  #include <linux/ctype.h>
  #include <linux/pci-p2pdma.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/genalloc.h>
  #include <linux/memremap.h>
  #include <linux/percpu-refcount.h>
  #include <linux/random.h>
  #include <linux/seq_buf.h>
  #include <linux/xarray.h>
  
  enum pci_p2pdma_map_type {
  	PCI_P2PDMA_MAP_UNKNOWN = 0,
  	PCI_P2PDMA_MAP_NOT_SUPPORTED,
  	PCI_P2PDMA_MAP_BUS_ADDR,
  	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
  };
  
  struct pci_p2pdma {
  	struct gen_pool *pool;
  	bool p2pmem_published;
  	struct xarray map_types;
  };
  
  struct pci_p2pdma_pagemap {
  	struct dev_pagemap pgmap;
  	struct pci_dev *provider;
  	u64 bus_offset;
  };
  
  static struct pci_p2pdma_pagemap *to_p2p_pgmap(struct dev_pagemap *pgmap)
  {
  	return container_of(pgmap, struct pci_p2pdma_pagemap, pgmap);
  }
  
  static ssize_t size_show(struct device *dev, struct device_attribute *attr,
  			 char *buf)
  {
  	struct pci_dev *pdev = to_pci_dev(dev);
  	size_t size = 0;
  
  	if (pdev->p2pdma->pool)
  		size = gen_pool_size(pdev->p2pdma->pool);
  
  	return snprintf(buf, PAGE_SIZE, "%zd\n", size);
  }
  static DEVICE_ATTR_RO(size);
  
  static ssize_t available_show(struct device *dev, struct device_attribute *attr,
  			      char *buf)
  {
  	struct pci_dev *pdev = to_pci_dev(dev);
  	size_t avail = 0;
  
  	if (pdev->p2pdma->pool)
  		avail = gen_pool_avail(pdev->p2pdma->pool);
  
  	return snprintf(buf, PAGE_SIZE, "%zd\n", avail);
  }
  static DEVICE_ATTR_RO(available);
  
  static ssize_t published_show(struct device *dev, struct device_attribute *attr,
  			      char *buf)
  {
  	struct pci_dev *pdev = to_pci_dev(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n",
  			pdev->p2pdma->p2pmem_published);
  }
  static DEVICE_ATTR_RO(published);
  
  static struct attribute *p2pmem_attrs[] = {
  	&dev_attr_size.attr,
  	&dev_attr_available.attr,
  	&dev_attr_published.attr,
  	NULL,
  };
  
  static const struct attribute_group p2pmem_group = {
  	.attrs = p2pmem_attrs,
  	.name = "p2pmem",
  };
  
  static void pci_p2pdma_release(void *data)
  {
  	struct pci_dev *pdev = data;
  	struct pci_p2pdma *p2pdma = pdev->p2pdma;
  
  	if (!p2pdma)
  		return;
  
  	/* Flush and disable pci_alloc_p2p_mem() */
  	pdev->p2pdma = NULL;
  	synchronize_rcu();
  
  	gen_pool_destroy(p2pdma->pool);
  	sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
  	xa_destroy(&p2pdma->map_types);
  }
  
  static int pci_p2pdma_setup(struct pci_dev *pdev)
  {
  	int error = -ENOMEM;
  	struct pci_p2pdma *p2p;
  
  	p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
  	if (!p2p)
  		return -ENOMEM;
  
  	xa_init(&p2p->map_types);
  
  	p2p->pool = gen_pool_create(PAGE_SHIFT, dev_to_node(&pdev->dev));
  	if (!p2p->pool)
  		goto out;
  
  	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
  	if (error)
  		goto out_pool_destroy;
  
  	pdev->p2pdma = p2p;
  
  	error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
  	if (error)
  		goto out_pool_destroy;
  
  	return 0;
  
  out_pool_destroy:
  	pdev->p2pdma = NULL;
  	gen_pool_destroy(p2p->pool);
  out:
  	devm_kfree(&pdev->dev, p2p);
  	return error;
  }
  
  /**
   * pci_p2pdma_add_resource - add memory for use as p2p memory
   * @pdev: the device to add the memory to
   * @bar: PCI BAR to add
   * @size: size of the memory to add, may be zero to use the whole BAR
   * @offset: offset into the PCI BAR
   *
   * The memory will be given ZONE_DEVICE struct pages so that it may
   * be used with any DMA request.
   */
  int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
  			    u64 offset)
  {
  	struct pci_p2pdma_pagemap *p2p_pgmap;
  	struct dev_pagemap *pgmap;
  	void *addr;
  	int error;
  
  	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
  		return -EINVAL;
  
  	if (offset >= pci_resource_len(pdev, bar))
  		return -EINVAL;
  
  	if (!size)
  		size = pci_resource_len(pdev, bar) - offset;
  
  	if (size + offset > pci_resource_len(pdev, bar))
  		return -EINVAL;
  
  	if (!pdev->p2pdma) {
  		error = pci_p2pdma_setup(pdev);
  		if (error)
  			return error;
  	}
  
  	p2p_pgmap = devm_kzalloc(&pdev->dev, sizeof(*p2p_pgmap), GFP_KERNEL);
  	if (!p2p_pgmap)
  		return -ENOMEM;
  
  	pgmap = &p2p_pgmap->pgmap;
  	pgmap->res.start = pci_resource_start(pdev, bar) + offset;
  	pgmap->res.end = pgmap->res.start + size - 1;
  	pgmap->res.flags = pci_resource_flags(pdev, bar);
  	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
  
  	p2p_pgmap->provider = pdev;
  	p2p_pgmap->bus_offset = pci_bus_address(pdev, bar) -
  		pci_resource_start(pdev, bar);
  
  	addr = devm_memremap_pages(&pdev->dev, pgmap);
  	if (IS_ERR(addr)) {
  		error = PTR_ERR(addr);
  		goto pgmap_free;
  	}
  
  	error = gen_pool_add_owner(pdev->p2pdma->pool, (unsigned long)addr,
  			pci_bus_address(pdev, bar) + offset,
  			resource_size(&pgmap->res), dev_to_node(&pdev->dev),
  			pgmap->ref);
  	if (error)
  		goto pages_free;
  
  	pci_info(pdev, "added peer-to-peer DMA memory %pR\n",
  		 &pgmap->res);
  
  	return 0;
  
  pages_free:
  	devm_memunmap_pages(&pdev->dev, pgmap);
  pgmap_free:
  	devm_kfree(&pdev->dev, pgmap);
  	return error;
  }
  EXPORT_SYMBOL_GPL(pci_p2pdma_add_resource);
  
  /*
   * Note this function returns the parent PCI device with a
   * reference taken. It is the caller's responsibility to drop
   * the reference.
   */
  static struct pci_dev *find_parent_pci_dev(struct device *dev)
  {
  	struct device *parent;
  
  	dev = get_device(dev);
  
  	while (dev) {
  		if (dev_is_pci(dev))
  			return to_pci_dev(dev);
  
  		parent = get_device(dev->parent);
  		put_device(dev);
  		dev = parent;
  	}
  
  	return NULL;
  }
  
  /*
   * Check if a PCI bridge has its ACS redirection bits set to redirect P2P
   * TLPs upstream via ACS. Returns 1 if the packets will be redirected
   * upstream, 0 otherwise.
   */
  static int pci_bridge_has_acs_redir(struct pci_dev *pdev)
  {
  	int pos;
  	u16 ctrl;
  
  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ACS);
  	if (!pos)
  		return 0;
  
  	pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);
  
  	if (ctrl & (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC))
  		return 1;
  
  	return 0;
  }
  
  static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
  {
  	if (!buf)
  		return;
  
  	seq_buf_printf(buf, "%s;", pci_name(pdev));
  }
  
  static const struct pci_p2pdma_whitelist_entry {
  	unsigned short vendor;
  	unsigned short device;
  	enum {
  		REQ_SAME_HOST_BRIDGE	= 1 << 0,
  	} flags;
  } pci_p2pdma_whitelist[] = {
  	/* AMD ZEN */
  	{PCI_VENDOR_ID_AMD,	0x1450,	0},
  
  	/* Intel Xeon E5/Core i7 */
  	{PCI_VENDOR_ID_INTEL,	0x3c00, REQ_SAME_HOST_BRIDGE},
  	{PCI_VENDOR_ID_INTEL,	0x3c01, REQ_SAME_HOST_BRIDGE},
  	/* Intel Xeon E7 v3/Xeon E5 v3/Core i7 */
  	{PCI_VENDOR_ID_INTEL,	0x2f00, REQ_SAME_HOST_BRIDGE},
  	{PCI_VENDOR_ID_INTEL,	0x2f01, REQ_SAME_HOST_BRIDGE},
  	{}
  };
  
  static bool __host_bridge_whitelist(struct pci_host_bridge *host,
  				    bool same_host_bridge)
  {
  	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
  	const struct pci_p2pdma_whitelist_entry *entry;
  	unsigned short vendor, device;
  
  	if (!root)
  		return false;
  
  	vendor = root->vendor;
  	device = root->device;
  	pci_dev_put(root);
  
  	for (entry = pci_p2pdma_whitelist; entry->vendor; entry++) {
  		if (vendor != entry->vendor || device != entry->device)
  			continue;
  		if (entry->flags & REQ_SAME_HOST_BRIDGE && !same_host_bridge)
  			return false;
  
  		return true;
  	}
  
  	return false;
  }
  
  /*
   * If we can't find a common upstream bridge take a look at the root
   * complex and compare it to a whitelist of known good hardware.
   */
  static bool host_bridge_whitelist(struct pci_dev *a, struct pci_dev *b)
  {
  	struct pci_host_bridge *host_a = pci_find_host_bridge(a->bus);
  	struct pci_host_bridge *host_b = pci_find_host_bridge(b->bus);
  
  	if (host_a == host_b)
  		return __host_bridge_whitelist(host_a, true);
  
  	if (__host_bridge_whitelist(host_a, false) &&
  	    __host_bridge_whitelist(host_b, false))
  		return true;
  
  	return false;
  }
  
  static enum pci_p2pdma_map_type
  __upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
  		int *dist, bool *acs_redirects, struct seq_buf *acs_list)
  {
  	struct pci_dev *a = provider, *b = client, *bb;
  	int dist_a = 0;
  	int dist_b = 0;
  	int acs_cnt = 0;
  
  	if (acs_redirects)
  		*acs_redirects = false;
  
  	/*
  	 * Note, we don't need to take references to devices returned by
  	 * pci_upstream_bridge() seeing we hold a reference to a child
  	 * device which will already hold a reference to the upstream bridge.
  	 */
  
  	while (a) {
  		dist_b = 0;
  
  		if (pci_bridge_has_acs_redir(a)) {
  			seq_buf_print_bus_devfn(acs_list, a);
  			acs_cnt++;
  		}
  
  		bb = b;
  
  		while (bb) {
  			if (a == bb)
  				goto check_b_path_acs;
  
  			bb = pci_upstream_bridge(bb);
  			dist_b++;
  		}
  
  		a = pci_upstream_bridge(a);
  		dist_a++;
  	}
  
  	if (dist)
  		*dist = dist_a + dist_b;
  
  	return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
  
  check_b_path_acs:
  	bb = b;
  
  	while (bb) {
  		if (a == bb)
  			break;
  
  		if (pci_bridge_has_acs_redir(bb)) {
  			seq_buf_print_bus_devfn(acs_list, bb);
  			acs_cnt++;
  		}
  
  		bb = pci_upstream_bridge(bb);
  	}
  
  	if (dist)
  		*dist = dist_a + dist_b;
  
  	if (acs_cnt) {
  		if (acs_redirects)
  			*acs_redirects = true;
  
  		return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
  	}
  
  	return PCI_P2PDMA_MAP_BUS_ADDR;
  }
  
  static unsigned long map_types_idx(struct pci_dev *client)
  {
  	return (pci_domain_nr(client->bus) << 16) |
  		(client->bus->number << 8) | client->devfn;
  }
  
  /*
   * Find the distance through the nearest common upstream bridge between
   * two PCI devices.
   *
   * If the two devices are the same device then 0 will be returned.
   *
   * If there are two virtual functions of the same device behind the same
   * bridge port then 2 will be returned (one step down to the PCIe switch,
   * then one step back to the same device).
   *
   * In the case where two devices are connected to the same PCIe switch, the
   * value 4 will be returned. This corresponds to the following PCI tree:
   *
   *     -+  Root Port
   *      \+ Switch Upstream Port
   *       +-+ Switch Downstream Port
   *       + \- Device A
   *       \-+ Switch Downstream Port
   *         \- Device B
   *
   * The distance is 4 because we traverse from Device A through the downstream
   * port of the switch, to the common upstream port, back up to the second
   * downstream port and then to Device B.
   *
   * Any two devices that cannot communicate using p2pdma will return
   * PCI_P2PDMA_MAP_NOT_SUPPORTED.
   *
   * Any two devices that have a data path that goes through the host bridge
   * will consult a whitelist. If the host bridges are on the whitelist,
   * this function will return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE.
   *
   * If either bridge is not on the whitelist this function returns
   * PCI_P2PDMA_MAP_NOT_SUPPORTED.
   *
   * If a bridge which has any ACS redirection bits set is in the path,
   * acs_redirects will be set to true. In this case, a list of all infringing
   * bridge addresses will be populated in acs_list (assuming it's non-null)
   * for printk purposes.
   */
  static enum pci_p2pdma_map_type
  upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
  		int *dist, bool *acs_redirects, struct seq_buf *acs_list)
  {
  	enum pci_p2pdma_map_type map_type;
  
  	map_type = __upstream_bridge_distance(provider, client, dist,
  					      acs_redirects, acs_list);
  
  	if (map_type == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE) {
  		if (!host_bridge_whitelist(provider, client))
  			map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;
  	}
  
  	if (provider->p2pdma)
  		xa_store(&provider->p2pdma->map_types, map_types_idx(client),
  			 xa_mk_value(map_type), GFP_KERNEL);
  
  	return map_type;
  }
  
  static enum pci_p2pdma_map_type
  upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
  			      int *dist)
  {
  	struct seq_buf acs_list;
  	bool acs_redirects;
  	int ret;
  
  	seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
  	if (!acs_list.buffer)
  		return -ENOMEM;
  
  	ret = upstream_bridge_distance(provider, client, dist, &acs_redirects,
  				       &acs_list);
  	if (acs_redirects) {
  		pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
  			 pci_name(provider));
  		/* Drop final semicolon */
  		acs_list.buffer[acs_list.len-1] = 0;
  		pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
  			 acs_list.buffer);
  	}
  
  	if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED) {
  		pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge or whitelisted host bridge\n",
  			 pci_name(provider));
  	}
  
  	kfree(acs_list.buffer);
  
  	return ret;
  }
  
  /**
   * pci_p2pdma_distance_many - Determine the cumulative distance between
   *	a p2pdma provider and the clients in use.
   * @provider: p2pdma provider to check against the client list
   * @clients: array of devices to check (NULL-terminated)
   * @num_clients: number of clients in the array
   * @verbose: if true, print warnings for devices when we return -1
   *
   * Returns -1 if any of the clients are not compatible, otherwise returns a
   * positive number where a lower number is the preferable choice. (If there's
   * one client that's the same as the provider it will return 0, which is best
   * choice).
   *
   * "compatible" means the provider and the clients are either all behind
   * the same PCI root port or the host bridges connected to each of the devices
   * are listed in the 'pci_p2pdma_whitelist'.
   */
  int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
  			     int num_clients, bool verbose)
  {
  	bool not_supported = false;
  	struct pci_dev *pci_client;
  	int total_dist = 0;
  	int distance;
  	int i, ret;
  
  	if (num_clients == 0)
  		return -1;
  
  	for (i = 0; i < num_clients; i++) {
  		if (IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
  		    clients[i]->dma_ops == &dma_virt_ops) {
  			if (verbose)
  				dev_warn(clients[i],
  					 "cannot be used for peer-to-peer DMA because the driver makes use of dma_virt_ops\n");
  			return -1;
  		}
  
  		pci_client = find_parent_pci_dev(clients[i]);
  		if (!pci_client) {
  			if (verbose)
  				dev_warn(clients[i],
  					 "cannot be used for peer-to-peer DMA as it is not a PCI device\n");
  			return -1;
  		}
  
  		if (verbose)
  			ret = upstream_bridge_distance_warn(provider,
  					pci_client, &distance);
  		else
  			ret = upstream_bridge_distance(provider, pci_client,
  						       &distance, NULL, NULL);
  
  		pci_dev_put(pci_client);
  
  		if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED)
  			not_supported = true;
  
  		if (not_supported && !verbose)
  			break;
  
  		total_dist += distance;
  	}
  
  	if (not_supported)
  		return -1;
  
  	return total_dist;
  }
  EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);
  
  /**
   * pci_has_p2pmem - check if a given PCI device has published any p2pmem
   * @pdev: PCI device to check
   */
  bool pci_has_p2pmem(struct pci_dev *pdev)
  {
  	return pdev->p2pdma && pdev->p2pdma->p2pmem_published;
  }
  EXPORT_SYMBOL_GPL(pci_has_p2pmem);
  
  /**
   * pci_p2pmem_find - find a peer-to-peer DMA memory device compatible with
   *	the specified list of clients and shortest distance (as determined
   *	by pci_p2pmem_dma())
   * @clients: array of devices to check (NULL-terminated)
   * @num_clients: number of client devices in the list
   *
   * If multiple devices are behind the same switch, the one "closest" to the
   * client devices in use will be chosen first. (So if one of the providers is
   * the same as one of the clients, that provider will be used ahead of any
   * other providers that are unrelated). If multiple providers are an equal
   * distance away, one will be chosen at random.
   *
   * Returns a pointer to the PCI device with a reference taken (use pci_dev_put
   * to return the reference) or NULL if no compatible device is found. The
   * found provider will also be assigned to the client list.
   */
  struct pci_dev *pci_p2pmem_find_many(struct device **clients, int num_clients)
  {
  	struct pci_dev *pdev = NULL;
  	int distance;
  	int closest_distance = INT_MAX;
  	struct pci_dev **closest_pdevs;
  	int dev_cnt = 0;
  	const int max_devs = PAGE_SIZE / sizeof(*closest_pdevs);
  	int i;
  
  	closest_pdevs = kmalloc(PAGE_SIZE, GFP_KERNEL);
  	if (!closest_pdevs)
  		return NULL;
  
  	while ((pdev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, pdev))) {
  		if (!pci_has_p2pmem(pdev))
  			continue;
  
  		distance = pci_p2pdma_distance_many(pdev, clients,
  						    num_clients, false);
  		if (distance < 0 || distance > closest_distance)
  			continue;
  
  		if (distance == closest_distance && dev_cnt >= max_devs)
  			continue;
  
  		if (distance < closest_distance) {
  			for (i = 0; i < dev_cnt; i++)
  				pci_dev_put(closest_pdevs[i]);
  
  			dev_cnt = 0;
  			closest_distance = distance;
  		}
  
  		closest_pdevs[dev_cnt++] = pci_dev_get(pdev);
  	}
  
  	if (dev_cnt)
  		pdev = pci_dev_get(closest_pdevs[prandom_u32_max(dev_cnt)]);
  
  	for (i = 0; i < dev_cnt; i++)
  		pci_dev_put(closest_pdevs[i]);
  
  	kfree(closest_pdevs);
  	return pdev;
  }
  EXPORT_SYMBOL_GPL(pci_p2pmem_find_many);
  
  /**
   * pci_alloc_p2p_mem - allocate peer-to-peer DMA memory
   * @pdev: the device to allocate memory from
   * @size: number of bytes to allocate
   *
   * Returns the allocated memory or NULL on error.
   */
  void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
  {
  	void *ret = NULL;
  	struct percpu_ref *ref;
  
  	/*
  	 * Pairs with synchronize_rcu() in pci_p2pdma_release() to
  	 * ensure pdev->p2pdma is non-NULL for the duration of the
  	 * read-lock.
  	 */
  	rcu_read_lock();
  	if (unlikely(!pdev->p2pdma))
  		goto out;
  
  	ret = (void *)gen_pool_alloc_owner(pdev->p2pdma->pool, size,
  			(void **) &ref);
  	if (!ret)
  		goto out;
  
  	if (unlikely(!percpu_ref_tryget_live(ref))) {
  		gen_pool_free(pdev->p2pdma->pool, (unsigned long) ret, size);
  		ret = NULL;
  		goto out;
  	}
  out:
  	rcu_read_unlock();
  	return ret;
  }
  EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);
  
  /**
   * pci_free_p2pmem - free peer-to-peer DMA memory
   * @pdev: the device the memory was allocated from
   * @addr: address of the memory that was allocated
   * @size: number of bytes that were allocated
   */
  void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
  {
  	struct percpu_ref *ref;
  
  	gen_pool_free_owner(pdev->p2pdma->pool, (uintptr_t)addr, size,
  			(void **) &ref);
  	percpu_ref_put(ref);
  }
  EXPORT_SYMBOL_GPL(pci_free_p2pmem);
  
  /**
   * pci_virt_to_bus - return the PCI bus address for a given virtual
   *	address obtained with pci_alloc_p2pmem()
   * @pdev: the device the memory was allocated from
   * @addr: address of the memory that was allocated
   */
  pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
  {
  	if (!addr)
  		return 0;
  	if (!pdev->p2pdma)
  		return 0;
  
  	/*
  	 * Note: when we added the memory to the pool we used the PCI
  	 * bus address as the physical address. So gen_pool_virt_to_phys()
  	 * actually returns the bus address despite the misleading name.
  	 */
  	return gen_pool_virt_to_phys(pdev->p2pdma->pool, (unsigned long)addr);
  }
  EXPORT_SYMBOL_GPL(pci_p2pmem_virt_to_bus);
  
  /**
   * pci_p2pmem_alloc_sgl - allocate peer-to-peer DMA memory in a scatterlist
   * @pdev: the device to allocate memory from
   * @nents: the number of SG entries in the list
   * @length: number of bytes to allocate
   *
   * Return: %NULL on error or &struct scatterlist pointer and @nents on success
   */
  struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
  					 unsigned int *nents, u32 length)
  {
  	struct scatterlist *sg;
  	void *addr;
  
  	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
  	if (!sg)
  		return NULL;
  
  	sg_init_table(sg, 1);
  
  	addr = pci_alloc_p2pmem(pdev, length);
  	if (!addr)
  		goto out_free_sg;
  
  	sg_set_buf(sg, addr, length);
  	*nents = 1;
  	return sg;
  
  out_free_sg:
  	kfree(sg);
  	return NULL;
  }
  EXPORT_SYMBOL_GPL(pci_p2pmem_alloc_sgl);
  
  /**
   * pci_p2pmem_free_sgl - free a scatterlist allocated by pci_p2pmem_alloc_sgl()
   * @pdev: the device to allocate memory from
   * @sgl: the allocated scatterlist
   */
  void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl)
  {
  	struct scatterlist *sg;
  	int count;
  
  	for_each_sg(sgl, sg, INT_MAX, count) {
  		if (!sg)
  			break;
  
  		pci_free_p2pmem(pdev, sg_virt(sg), sg->length);
  	}
  	kfree(sgl);
  }
  EXPORT_SYMBOL_GPL(pci_p2pmem_free_sgl);
  
  /**
   * pci_p2pmem_publish - publish the peer-to-peer DMA memory for use by
   *	other devices with pci_p2pmem_find()
   * @pdev: the device with peer-to-peer DMA memory to publish
   * @publish: set to true to publish the memory, false to unpublish it
   *
   * Published memory can be used by other PCI device drivers for
   * peer-2-peer DMA operations. Non-published memory is reserved for
   * exclusive use of the device driver that registers the peer-to-peer
   * memory.
   */
  void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
  {
  	if (pdev->p2pdma)
  		pdev->p2pdma->p2pmem_published = publish;
  }
  EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
  
  static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider,
  						    struct pci_dev *client)
  {
  	if (!provider->p2pdma)
  		return PCI_P2PDMA_MAP_NOT_SUPPORTED;
  
  	return xa_to_value(xa_load(&provider->p2pdma->map_types,
  				   map_types_idx(client)));
  }
  
  static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap,
  		struct device *dev, struct scatterlist *sg, int nents)
  {
  	struct scatterlist *s;
  	phys_addr_t paddr;
  	int i;
  
  	/*
  	 * p2pdma mappings are not compatible with devices that use
  	 * dma_virt_ops. If the upper layers do the right thing
  	 * this should never happen because it will be prevented
  	 * by the check in pci_p2pdma_distance_many()
  	 */
  	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
  			 dev->dma_ops == &dma_virt_ops))
  		return 0;
  
  	for_each_sg(sg, s, nents, i) {
  		paddr = sg_phys(s);
  
  		s->dma_address = paddr - p2p_pgmap->bus_offset;
  		sg_dma_len(s) = s->length;
  	}
  
  	return nents;
  }
  
  /**
   * pci_p2pdma_map_sg - map a PCI peer-to-peer scatterlist for DMA
   * @dev: device doing the DMA request
   * @sg: scatter list to map
   * @nents: elements in the scatterlist
   * @dir: DMA direction
   * @attrs: DMA attributes passed to dma_map_sg() (if called)
   *
   * Scatterlists mapped with this function should be unmapped using
   * pci_p2pdma_unmap_sg_attrs().
   *
   * Returns the number of SG entries mapped or 0 on error.
   */
  int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
  		int nents, enum dma_data_direction dir, unsigned long attrs)
  {
  	struct pci_p2pdma_pagemap *p2p_pgmap =
  		to_p2p_pgmap(sg_page(sg)->pgmap);
  	struct pci_dev *client;
  
  	if (WARN_ON_ONCE(!dev_is_pci(dev)))
  		return 0;
  
  	client = to_pci_dev(dev);
  
  	switch (pci_p2pdma_map_type(p2p_pgmap->provider, client)) {
  	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
  		return dma_map_sg_attrs(dev, sg, nents, dir, attrs);
  	case PCI_P2PDMA_MAP_BUS_ADDR:
  		return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents);
  	default:
  		WARN_ON_ONCE(1);
  		return 0;
  	}
  }
  EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg_attrs);
  
  /**
   * pci_p2pdma_unmap_sg - unmap a PCI peer-to-peer scatterlist that was
   *	mapped with pci_p2pdma_map_sg()
   * @dev: device doing the DMA request
   * @sg: scatter list to map
   * @nents: number of elements returned by pci_p2pdma_map_sg()
   * @dir: DMA direction
   * @attrs: DMA attributes passed to dma_unmap_sg() (if called)
   */
  void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
  		int nents, enum dma_data_direction dir, unsigned long attrs)
  {
  	struct pci_p2pdma_pagemap *p2p_pgmap =
  		to_p2p_pgmap(sg_page(sg)->pgmap);
  	enum pci_p2pdma_map_type map_type;
  	struct pci_dev *client;
  
  	if (WARN_ON_ONCE(!dev_is_pci(dev)))
  		return;
  
  	client = to_pci_dev(dev);
  
  	map_type = pci_p2pdma_map_type(p2p_pgmap->provider, client);
  
  	if (map_type == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE)
  		dma_unmap_sg_attrs(dev, sg, nents, dir, attrs);
  }
  EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
  
  /**
   * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
   *		to enable p2pdma
   * @page: contents of the value to be stored
   * @p2p_dev: returns the PCI device that was selected to be used
   *		(if one was specified in the stored value)
   * @use_p2pdma: returns whether to enable p2pdma or not
   *
   * Parses an attribute value to decide whether to enable p2pdma.
   * The value can select a PCI device (using its full BDF device
   * name) or a boolean (in any format strtobool() accepts). A false
   * value disables p2pdma, a true value expects the caller
   * to automatically find a compatible device and specifying a PCI device
   * expects the caller to use the specific provider.
   *
   * pci_p2pdma_enable_show() should be used as the show operation for
   * the attribute.
   *
   * Returns 0 on success
   */
  int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
  			    bool *use_p2pdma)
  {
  	struct device *dev;
  
  	dev = bus_find_device_by_name(&pci_bus_type, NULL, page);
  	if (dev) {
  		*use_p2pdma = true;
  		*p2p_dev = to_pci_dev(dev);
  
  		if (!pci_has_p2pmem(*p2p_dev)) {
  			pci_err(*p2p_dev,
  				"PCI device has no peer-to-peer memory: %s\n",
  				page);
  			pci_dev_put(*p2p_dev);
  			return -ENODEV;
  		}
  
  		return 0;
  	} else if ((page[0] == '0' || page[0] == '1') && !iscntrl(page[1])) {
  		/*
  		 * If the user enters a PCI device that  doesn't exist
  		 * like "0000:01:00.1", we don't want strtobool to think
  		 * it's a '0' when it's clearly not what the user wanted.
  		 * So we require 0's and 1's to be exactly one character.
  		 */
  	} else if (!strtobool(page, use_p2pdma)) {
  		return 0;
  	}
  
  	pr_err("No such PCI device: %.*s\n", (int)strcspn(page, "\n"), page);
  	return -ENODEV;
  }
  EXPORT_SYMBOL_GPL(pci_p2pdma_enable_store);
  
  /**
   * pci_p2pdma_enable_show - show a configfs/sysfs attribute indicating
   *		whether p2pdma is enabled
   * @page: contents of the stored value
   * @p2p_dev: the selected p2p device (NULL if no device is selected)
   * @use_p2pdma: whether p2pdma has been enabled
   *
   * Attributes that use pci_p2pdma_enable_store() should use this function
   * to show the value of the attribute.
   *
   * Returns 0 on success
   */
  ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
  			       bool use_p2pdma)
  {
  	if (!use_p2pdma)
  		return sprintf(page, "0\n");
  
  	if (!p2p_dev)
  		return sprintf(page, "1\n");
  
  	return sprintf(page, "%s\n", pci_name(p2p_dev));
  }
  EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);
  