[PATCH v2 01/10] PCI/P2PDMA: Support peer to peer memory

[Logan Gunthorpe]

Some PCI devices may have memory mapped in a BAR space that's
intended for use in Peer-to-Peer transactions. In order to enable
such transactions the memory must be registered with ZONE_DEVICE pages
so it can be used by DMA interfaces in existing drivers.

A kernel interface is provided so that other subsystems can find and
allocate chunks of P2P memory as necessary to facilitate transfers
between two PCI peers. Depending on hardware, this may reduce the
bandwidth of the transfer but would significantly reduce pressure
on system memory. This may be desirable in many cases: for example a
system could be designed with a small CPU connected to a PCI switch by a
small number of lanes which would maximize the number of lanes available
to connect to NVME devices.

The interface requires a user driver to collect a list of client devices
involved in the transaction with the pci_p2pmem_add_client*() functions
then call pci_p2pmem_find() to obtain any suitable P2P memory. Once
this is done the list is bound to the memory and the calling driver is
free to add and remove clients as necessary. The ACS bits on the
downstream switch port will be managed for all the registered clients.

The code is designed to only utilize the p2pmem device if all the devices
involved in a transfer are behind the same PCI switch. This is because
using P2P transactions through the PCI root complex can have performance
limitations or, worse, might not work at all. Finding out how well a
particular RC supports P2P transfers is non-trivial. Additionally, the
benefits of P2P transfers that go through the RC is limited to only
reducing DRAM usage.

This commit includes significant rework and feedback from Christoph
Hellwig.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 drivers/pci/Kconfig        |  16 ++
 drivers/pci/Makefile       |   1 +
 drivers/pci/p2pdma.c       | 568 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/memremap.h   |  18 ++
 include/linux/pci-p2pdma.h |  87 +++++++
 include/linux/pci.h        |   4 +
 6 files changed, 694 insertions(+)
 create mode 100644 drivers/pci/p2pdma.c
 create mode 100644 include/linux/pci-p2pdma.h

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 34b56a8f8480..840831418cbd 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -124,6 +124,22 @@ config PCI_PASID
 
 	  If unsure, say N.
 
+config PCI_P2PDMA
+	bool "PCI Peer to Peer transfer support"
+	depends on ZONE_DEVICE
+	select GENERIC_ALLOCATOR
+	help
+	  EnableÑ drivers to do PCI peer to peer transactions to and from
+	  BARs that are exposed in other devices that are the part of
+	  the hierarchy where peer-to-peer DMA is guaranteed by the PCI
+	  specification to work (ie. anything below a single PCI bridge).
+
+	  Many PCIe root complexes do not support P2P transactions and
+	  it's hard to tell which support it with good performance, so
+	  at this time you will need a PCIe switch.
+
+	  If unsure, say N.
+
 config PCI_LABEL
 	def_bool y if (DMI || ACPI)
 	depends on PCI
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index 941970936840..45e0ff6f3213 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -26,6 +26,7 @@ obj-$(CONFIG_PCI_MSI) += msi.o
 
 obj-$(CONFIG_PCI_ATS) += ats.o
 obj-$(CONFIG_PCI_IOV) += iov.o
+obj-$(CONFIG_PCI_P2PDMA) += p2pdma.o
 
 #
 # ACPI Related PCI FW Functions
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
new file mode 100644
index 000000000000..ec0a6cb9e500
--- /dev/null
+++ b/drivers/pci/p2pdma.c
@@ -0,0 +1,568 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PCI Peer 2 Peer DMA support.
+ *
+ * Copyright (c) 2016-2017, Microsemi Corporation
+ * Copyright (c) 2017, Christoph Hellwig.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ */
+
+#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>
+
+struct pci_p2pdma {
+	struct percpu_ref devmap_ref;
+	struct completion devmap_ref_done;
+	struct gen_pool *pool;
+	bool published;
+};
+
+static void pci_p2pdma_percpu_release(struct percpu_ref *ref)
+{
+	struct pci_p2pdma *p2p =
+		container_of(ref, struct pci_p2pdma, devmap_ref);
+
+	complete_all(&p2p->devmap_ref_done);
+}
+
+static void pci_p2pdma_percpu_kill(void *data)
+{
+	struct percpu_ref *ref = data;
+
+	if (percpu_ref_is_dying(ref))
+		return;
+
+	percpu_ref_kill(ref);
+}
+
+static void pci_p2pdma_release(void *data)
+{
+	struct pci_dev *pdev = data;
+
+	wait_for_completion(&pdev->p2pdma->devmap_ref_done);
+	percpu_ref_exit(&pdev->p2pdma->devmap_ref);
+
+	gen_pool_destroy(pdev->p2pdma->pool);
+	pdev->p2pdma = NULL;
+}
+
+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;
+
+	p2p->pool = gen_pool_create(PAGE_SHIFT, dev_to_node(&pdev->dev));
+	if (!p2p->pool)
+		goto out;
+
+	init_completion(&p2p->devmap_ref_done);
+	error = percpu_ref_init(&p2p->devmap_ref,
+			pci_p2pdma_percpu_release, 0, GFP_KERNEL);
+	if (error)
+		goto out_pool_destroy;
+
+	percpu_ref_switch_to_atomic_sync(&p2p->devmap_ref);
+
+	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
+	if (error)
+		goto out_pool_destroy;
+
+	pdev->p2pdma = p2p;
+
+	return 0;
+
+out_pool_destroy:
+	gen_pool_destroy(p2p->pool);
+out:
+	devm_kfree(&pdev->dev, p2p);
+	return error;
+}
+
+/**
+ * pci_p2pdma_add_resource - add memory for use as p2p memory
+ * @pci: 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 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;
+	}
+
+	pgmap = devm_kzalloc(&pdev->dev, sizeof(*pgmap), GFP_KERNEL);
+	if (!pgmap)
+		return -ENOMEM;
+
+	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->ref = &pdev->p2pdma->devmap_ref;
+	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
+
+	addr = devm_memremap_pages(&pdev->dev, pgmap);
+	if (IS_ERR(addr))
+		return PTR_ERR(addr);
+
+	error = gen_pool_add_virt(pdev->p2pdma->pool, (uintptr_t)addr,
+			pci_bus_address(pdev, bar) + offset,
+			resource_size(&pgmap->res), dev_to_node(&pdev->dev));
+	if (error)
+		return error;
+
+	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_percpu_kill,
+					  &pdev->p2pdma->devmap_ref);
+	if (error)
+		return error;
+
+	dev_info(&pdev->dev, "added peer-to-peer DMA memory %pR\n",
+		 &pgmap->res);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_add_resource);
+
+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;
+}
+
+/*
+ * If a device is behind a switch, we try to find the upstream bridge
+ * port of the switch. This requires two calls to pci_upstream_bridge:
+ * one for the upstream port on the switch, one on the upstream port
+ * for the next level in the hierarchy. Because of this, devices connected
+ * to the root port will be rejected.
+ */
+static struct pci_dev *get_upstream_bridge_port(struct pci_dev *pdev)
+{
+	struct pci_dev *up1, *up2;
+
+	if (!pdev)
+		return NULL;
+
+	up1 = pci_dev_get(pci_upstream_bridge(pdev));
+	if (!up1)
+		return NULL;
+
+	up2 = pci_dev_get(pci_upstream_bridge(up1));
+	pci_dev_put(up1);
+
+	return up2;
+}
+
+static bool __upstream_bridges_match(struct pci_dev *upstream,
+				     struct pci_dev *client)
+{
+	struct pci_dev *dma_up;
+	bool ret = true;
+
+	dma_up = get_upstream_bridge_port(client);
+
+	if (!dma_up) {
+		dev_dbg(&client->dev, "not a PCI device behind a bridge\n");
+		ret = false;
+		goto out;
+	}
+
+	if (upstream != dma_up) {
+		dev_dbg(&client->dev,
+			"does not reside on the same upstream bridge\n");
+		ret = false;
+		goto out;
+	}
+
+out:
+	pci_dev_put(dma_up);
+	return ret;
+}
+
+static bool upstream_bridges_match(struct pci_dev *pdev,
+				   struct pci_dev *client)
+{
+	struct pci_dev *upstream;
+	bool ret;
+
+	upstream = get_upstream_bridge_port(pdev);
+	if (!upstream) {
+		dev_warn(&pdev->dev, "not behind a PCI bridge\n");
+		return false;
+	}
+
+	ret = __upstream_bridges_match(upstream, client);
+
+	pci_dev_put(upstream);
+
+	return ret;
+}
+
+struct pci_p2pdma_client {
+	struct list_head list;
+	struct pci_dev *client;
+	struct pci_dev *p2pdma;
+};
+
+/**
+ * pci_p2pdma_add_client - allocate a new element in a client device list
+ * @head: list head of p2pdma clients
+ * @dev: device to add to the list
+ *
+ * This adds @dev to a list of clients used by a p2pdma device.
+ * This list should be passed to p2pmem_find(). Once p2pmem_find() has
+ * been called successfully, the list will be bound to a specific p2pdma
+ * device and new clients can only be added to the list if they are
+ * supported by that p2pdma device.
+ *
+ * The caller is expected to have a lock which protects @head as necessary
+ * so that none of the pci_p2p functions can be called concurrently
+ * on that list.
+ *
+ * Returns 0 if the client was successfully added.
+ */
+int pci_p2pdma_add_client(struct list_head *head, struct device *dev)
+{
+	struct pci_p2pdma_client *item, *new_item;
+	struct pci_dev *p2pdma = NULL;
+	struct pci_dev *client;
+	int ret;
+
+	if (IS_ENABLED(CONFIG_DMA_VIRT_OPS) && dev->dma_ops == &dma_virt_ops) {
+		dev_warn(dev,
+			 "cannot be used for peer-to-peer DMA because the driver makes use of dma_virt_ops\n");
+		return -ENODEV;
+	}
+
+
+	client = find_parent_pci_dev(dev);
+	if (!client) {
+		dev_warn(dev,
+			 "cannot be used for peer-to-peer DMA as it is not a PCI device\n");
+		return -ENODEV;
+	}
+
+	item = list_first_entry_or_null(head, struct pci_p2pdma_client, list);
+	if (item && item->p2pdma) {
+		p2pdma = item->p2pdma;
+
+		if (!upstream_bridges_match(p2pdma, client)) {
+			ret = -EXDEV;
+			goto put_client;
+		}
+	}
+
+	new_item = kzalloc(sizeof(*new_item), GFP_KERNEL);
+	if (!new_item) {
+		ret = -ENOMEM;
+		goto put_client;
+	}
+
+	new_item->client = client;
+	new_item->p2pdma = pci_dev_get(p2pdma);
+
+	list_add_tail(&new_item->list, head);
+
+	return 0;
+
+put_client:
+	pci_dev_put(client);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_add_client);
+
+static void pci_p2pdma_client_free(struct pci_p2pdma_client *item)
+{
+	list_del(&item->list);
+	pci_dev_put(item->client);
+	pci_dev_put(item->p2pdma);
+	kfree(item);
+}
+
+/**
+ * pci_p2pdma_remove_client - remove and free a new p2pdma client
+ * @head: list head of p2pdma clients
+ * @dev: device to remove from the list
+ *
+ * This removes @dev from a list of clients used by a p2pdma device.
+ * The caller is expected to have a lock which protects @head as necessary
+ * so that none of the pci_p2p functions can be called concurrently
+ * on that list.
+ */
+void pci_p2pdma_remove_client(struct list_head *head, struct device *dev)
+{
+	struct pci_p2pdma_client *pos, *tmp;
+	struct pci_dev *pdev;
+
+	pdev = find_parent_pci_dev(dev);
+	if (!pdev)
+		return;
+
+	list_for_each_entry_safe(pos, tmp, head, list) {
+		if (pos->client != pdev)
+			continue;
+
+		pci_p2pdma_client_free(pos);
+	}
+
+	pci_dev_put(pdev);
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_remove_client);
+
+/**
+ * pci_p2pdma_client_list_free - free an entire list of p2pdma clients
+ * @head: list head of p2pdma clients
+ *
+ * This removes all devices in a list of clients used by a p2pdma device.
+ * The caller is expected to have a lock which protects @head as necessary
+ * so that none of the pci_p2pdma functions can be called concurrently
+ * on that list.
+ */
+void pci_p2pdma_client_list_free(struct list_head *head)
+{
+	struct pci_p2pdma_client *pos, *tmp;
+
+	list_for_each_entry_safe(pos, tmp, head, list)
+		pci_p2pdma_client_free(pos);
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_client_list_free);
+
+static bool upstream_bridges_match_list(struct pci_dev *pdev,
+					struct list_head *head)
+{
+	struct pci_p2pdma_client *pos;
+	struct pci_dev *upstream;
+	bool ret;
+
+	upstream = get_upstream_bridge_port(pdev);
+	if (!upstream) {
+		dev_warn(&pdev->dev, "not behind a PCI bridge\n");
+		return false;
+	}
+
+	list_for_each_entry(pos, head, list) {
+		ret = __upstream_bridges_match(upstream, pos->client);
+		if (!ret)
+			break;
+	}
+
+	pci_dev_put(upstream);
+	return ret;
+}
+
+/**
+ * pci_p2pmem_find - find a peer-to-peer DMA memory device compatible with
+ *	the specified list of clients
+ * @dev: list of devices to check (NULL-terminated)
+ *
+ * For now, we only support cases where the devices that will transfer to the
+ * p2pmem device are behind the same bridge. This cuts out cases that may work
+ * but is safest for the user.
+ *
+ * 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.
+ */
+struct pci_dev *pci_p2pmem_find(struct list_head *clients)
+{
+	struct pci_dev *pdev = NULL;
+	struct pci_p2pdma_client *pos;
+
+	while ((pdev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, pdev))) {
+		if (!pdev->p2pdma || !pdev->p2pdma->published)
+			continue;
+
+		if (!upstream_bridges_match_list(pdev, clients))
+			continue;
+
+		list_for_each_entry(pos, clients, list)
+			pos->p2pdma = pdev;
+
+		return pdev;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_find);
+
+/**
+ * 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;
+
+	if (unlikely(!pdev->p2pdma))
+		return NULL;
+
+	if (unlikely(!percpu_ref_tryget_live(&pdev->p2pdma->devmap_ref)))
+		return NULL;
+
+	ret = (void *)(uintptr_t)gen_pool_alloc(pdev->p2pdma->pool, size);
+
+	if (unlikely(!ret))
+		percpu_ref_put(&pdev->p2pdma->devmap_ref);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);
+
+/**
+ * pci_free_p2pmem - allocate 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 was allocated
+ */
+void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
+{
+	gen_pool_free(pdev->p2pdma->pool, (uintptr_t)addr, size);
+	percpu_ref_put(&pdev->p2pdma->devmap_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 an scatterlist
+ * @pdev:	the device to allocate memory from
+ * @sgl:	the allocated scatterlist
+ * @nents:      the number of SG entries in the list
+ * @length:     number of bytes to allocate
+ *
+ * Returns 0 on success
+ */
+int pci_p2pmem_alloc_sgl(struct pci_dev *pdev, struct scatterlist **sgl,
+			 unsigned int *nents, u32 length)
+{
+	struct scatterlist *sg;
+	void *addr;
+
+	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
+	if (!sg)
+		return -ENOMEM;
+
+	sg_init_table(sg, 1);
+
+	addr = pci_alloc_p2pmem(pdev, length);
+	if (!addr)
+		goto out_free_sg;
+
+	sg_set_buf(sg, addr, length);
+	*sgl = sg;
+	*nents = 1;
+	return 0;
+
+out_free_sg:
+	kfree(sg);
+	return -ENOMEM;
+}
+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
+ * @nents:      the number of SG entries in the list
+ */
+void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl,
+			 unsigned int nents)
+{
+	struct scatterlist *sg;
+	int count;
+
+	if (!sgl || !nents)
+		return;
+
+	for_each_sg(sgl, sg, nents, count)
+		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
+ */
+void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
+{
+	if (publish && !pdev->p2pdma)
+		return;
+
+	pdev->p2pdma->published = publish;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 7b4899c06f49..9e907c338a44 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -53,11 +53,16 @@ struct vmem_altmap {
  * driver can hotplug the device memory using ZONE_DEVICE and with that memory
  * type. Any page of a process can be migrated to such memory. However no one
  * should be allow to pin such memory so that it can always be evicted.
+ *
+ * MEMORY_DEVICE_PCI_P2PDMA:
+ * Device memory residing in a PCI BAR intended for use with Peer-to-Peer
+ * transactions.
  */
 enum memory_type {
 	MEMORY_DEVICE_HOST = 0,
 	MEMORY_DEVICE_PRIVATE,
 	MEMORY_DEVICE_PUBLIC,
+	MEMORY_DEVICE_PCI_P2PDMA,
 };
 
 /*
@@ -161,6 +166,19 @@ static inline void vmem_altmap_free(struct vmem_altmap *altmap,
 }
 #endif /* CONFIG_ZONE_DEVICE */
 
+#ifdef CONFIG_PCI_P2PDMA
+static inline bool is_pci_p2pdma_page(const struct page *page)
+{
+	return is_zone_device_page(page) &&
+		page->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
+}
+#else /* CONFIG_PCI_P2PDMA */
+static inline bool is_pci_p2pdma_page(const struct page *page)
+{
+	return false;
+}
+#endif /* CONFIG_PCI_P2PDMA */
+
 #if defined(CONFIG_DEVICE_PRIVATE) || defined(CONFIG_DEVICE_PUBLIC)
 static inline bool is_device_private_page(const struct page *page)
 {
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
new file mode 100644
index 000000000000..c0dde3d3aac4
--- /dev/null
+++ b/include/linux/pci-p2pdma.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2016-2017, Microsemi Corporation
+ * Copyright (c) 2017, Christoph Hellwig.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ */
+
+#ifndef _LINUX_PCI_P2PDMA_H
+#define _LINUX_PCI_P2PDMA_H
+
+#include <linux/pci.h>
+
+struct block_device;
+struct scatterlist;
+
+#ifdef CONFIG_PCI_P2PDMA
+int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
+		u64 offset);
+int pci_p2pdma_add_client(struct list_head *head, struct device *dev);
+void pci_p2pdma_remove_client(struct list_head *head, struct device *dev);
+void pci_p2pdma_client_list_free(struct list_head *head);
+struct pci_dev *pci_p2pmem_find(struct list_head *clients);
+void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size);
+void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size);
+pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr);
+int pci_p2pmem_alloc_sgl(struct pci_dev *pdev, struct scatterlist **sgl,
+		unsigned int *nents, u32 length);
+void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl,
+		unsigned int nents);
+void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
+#else /* CONFIG_PCI_P2PDMA */
+static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
+		size_t size, u64 offset)
+{
+	return 0;
+}
+static inline int pci_p2pdma_add_client(struct list_head *head,
+		struct device *dev)
+{
+	return 0;
+}
+static inline void pci_p2pdma_remove_client(struct list_head *head,
+		struct device *dev)
+{
+}
+static inline void pci_p2pdma_client_list_free(struct list_head *head)
+{
+}
+static inline struct pci_dev *pci_p2pmem_find(struct list_head *clients)
+{
+	return NULL;
+}
+static inline void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
+{
+	return NULL;
+}
+static inline void pci_free_p2pmem(struct pci_dev *pdev, void *addr,
+		size_t size)
+{
+}
+static inline pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev,
+						    void *addr)
+{
+	return 0;
+}
+static inline int pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
+		struct scatterlist **sgl, unsigned int *nents, u32 length)
+{
+	return -ENODEV;
+}
+static inline void pci_p2pmem_free_sgl(struct pci_dev *pdev,
+		struct scatterlist *sgl, unsigned int nents)
+{
+}
+static inline void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
+{
+}
+#endif /* CONFIG_PCI_P2PDMA */
+#endif /* _LINUX_PCI_P2P_H */
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 024a1beda008..437e42615896 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -276,6 +276,7 @@ struct pcie_link_state;
 struct pci_vpd;
 struct pci_sriov;
 struct pci_ats;
+struct pci_p2pdma;
 
 /* The pci_dev structure describes PCI devices */
 struct pci_dev {
@@ -429,6 +430,9 @@ struct pci_dev {
 #ifdef CONFIG_PCI_PASID
 	u16		pasid_features;
 #endif
+#ifdef CONFIG_PCI_P2PDMA
+	struct pci_p2pdma *p2pdma;
+#endif
 	phys_addr_t	rom;		/* Physical address if not from BAR */
 	size_t		romlen;		/* Length if not from BAR */
 	char		*driver_override; /* Driver name to force a match */
-- 
2.11.0