Merge tag 'pci-v4.20-changes' of git://git.kernel.org/pub/scm/linux/k…

…ernel/git/helgaas/pci

Pull PCI updates from Bjorn Helgaas:

 - Fix ASPM link_state teardown on removal (Lukas Wunner)

 - Fix misleading _OSC ASPM message (Sinan Kaya)

 - Make _OSC optional for PCI (Sinan Kaya)

 - Don't initialize ASPM link state when ACPI_FADT_NO_ASPM is set
   (Patrick Talbert)

 - Remove x86 and arm64 node-local allocation for host bridge structures
   (Punit Agrawal)

 - Pay attention to device-specific _PXM node values (Jonathan Cameron)

 - Support new Immediate Readiness bit (Felipe Balbi)

 - Differentiate between pciehp surprise and safe removal (Lukas Wunner)

 - Remove unnecessary pciehp includes (Lukas Wunner)

 - Drop pciehp hotplug_slot_ops wrappers (Lukas Wunner)

 - Tolerate PCIe Slot Presence Detect being hardwired to zero to
   workaround broken hardware, e.g., the Wilocity switch/wireless device
   (Lukas Wunner)

 - Unify pciehp controller & slot structs (Lukas Wunner)

 - Constify hotplug_slot_ops (Lukas Wunner)

 - Drop hotplug_slot_info (Lukas Wunner)

 - Embed hotplug_slot struct into users instead of allocating it
   separately (Lukas Wunner)

 - Initialize PCIe port service drivers directly instead of relying on
   initcall ordering (Keith Busch)

 - Restore PCI config state after a slot reset (Keith Busch)

 - Save/restore DPC config state along with other PCI config state
   (Keith Busch)

 - Reference count devices during AER handling to avoid race issue with
   concurrent hot removal (Keith Busch)

 - If an Upstream Port reports ERR_FATAL, don't try to read the Port's
   config space because it is probably unreachable (Keith Busch)

 - During error handling, use slot-specific reset instead of secondary
   bus reset to avoid link up/down issues on hotplug ports (Keith Busch)

 - Restore previous AER/DPC handling that does not remove and
   re-enumerate devices on ERR_FATAL (Keith Busch)

 - Notify all drivers that may be affected by error recovery resets
   (Keith Busch)

 - Always generate error recovery uevents, even if a driver doesn't have
   error callbacks (Keith Busch)

 - Make PCIe link active reporting detection generic (Keith Busch)

 - Support D3cold in PCIe hierarchies during system sleep and runtime,
   including hotplug and Thunderbolt ports (Mika Westerberg)

 - Handle hpmemsize/hpiosize kernel parameters uniformly, whether slots
   are empty or occupied (Jon Derrick)

 - Remove duplicated include from pci/pcie/err.c and unused variable
   from cpqphp (YueHaibing)

 - Remove driver pci_cleanup_aer_uncorrect_error_status() calls (Oza
   Pawandeep)

 - Uninline PCI bus accessors for better ftracing (Keith Busch)

 - Remove unused AER Root Port .error_resume method (Keith Busch)

 - Use kfifo in AER instead of a local version (Keith Busch)

 - Use threaded IRQ in AER bottom half (Keith Busch)

 - Use managed resources in AER core (Keith Busch)

 - Reuse pcie_port_find_device() for AER injection (Keith Busch)

 - Abstract AER interrupt handling to disconnect error injection (Keith
   Busch)

 - Refactor AER injection callbacks to simplify future improvments
   (Keith Busch)

 - Remove unused Netronome NFP32xx Device IDs (Jakub Kicinski)

 - Use bitmap_zalloc() for dma_alias_mask (Andy Shevchenko)

 - Add switch fall-through annotations (Gustavo A. R. Silva)

 - Remove unused Switchtec quirk variable (Joshua Abraham)

 - Fix pci.c kernel-doc warning (Randy Dunlap)

 - Remove trivial PCI wrappers for DMA APIs (Christoph Hellwig)

 - Add Intel GPU device IDs to spurious interrupt quirk (Bin Meng)

 - Run Switchtec DMA aliasing quirk only on NTB endpoints to avoid
   useless dmesg errors (Logan Gunthorpe)

 - Update Switchtec NTB documentation (Wesley Yung)

 - Remove redundant "default n" from Kconfig (Bartlomiej Zolnierkiewicz)

 - Avoid panic when drivers enable MSI/MSI-X twice (Tonghao Zhang)

 - Add PCI support for peer-to-peer DMA (Logan Gunthorpe)

 - Add sysfs group for PCI peer-to-peer memory statistics (Logan
   Gunthorpe)

 - Add PCI peer-to-peer DMA scatterlist mapping interface (Logan
   Gunthorpe)

 - Add PCI configfs/sysfs helpers for use by peer-to-peer users (Logan
   Gunthorpe)

 - Add PCI peer-to-peer DMA driver writer's documentation (Logan
   Gunthorpe)

 - Add block layer flag to indicate driver support for PCI peer-to-peer
   DMA (Logan Gunthorpe)

 - Map Infiniband scatterlists for peer-to-peer DMA if they contain P2P
   memory (Logan Gunthorpe)

 - Register nvme-pci CMB buffer as PCI peer-to-peer memory (Logan
   Gunthorpe)

 - Add nvme-pci support for PCI peer-to-peer memory in requests (Logan
   Gunthorpe)

 - Use PCI peer-to-peer memory in nvme (Stephen Bates, Steve Wise,
   Christoph Hellwig, Logan Gunthorpe)

 - Cache VF config space size to optimize enumeration of many VFs
   (KarimAllah Ahmed)

 - Remove unnecessary <linux/pci-ats.h> include (Bjorn Helgaas)

 - Fix VMD AERSID quirk Device ID matching (Jon Derrick)

 - Fix Cadence PHY handling during probe (Alan Douglas)

 - Signal Cadence Endpoint interrupts via AXI region 0 instead of last
   region (Alan Douglas)

 - Write Cadence Endpoint MSI interrupts with 32 bits of data (Alan
   Douglas)

 - Remove redundant controller tests for "device_type == pci" (Rob
   Herring)

 - Document R-Car E3 (R8A77990) bindings (Tho Vu)

 - Add device tree support for R-Car r8a7744 (Biju Das)

 - Drop unused mvebu PCIe capability code (Thomas Petazzoni)

 - Add shared PCI bridge emulation code (Thomas Petazzoni)

 - Convert mvebu to use shared PCI bridge emulation (Thomas Petazzoni)

 - Add aardvark Root Port emulation (Thomas Petazzoni)

 - Support 100MHz/200MHz refclocks for i.MX6 (Lucas Stach)

 - Add initial power management for i.MX7 (Leonard Crestez)

 - Add PME_Turn_Off support for i.MX7 (Leonard Crestez)

 - Fix qcom runtime power management error handling (Bjorn Andersson)

 - Update TI dra7xx unaligned access errata workaround for host mode as
   well as endpoint mode (Vignesh R)

 - Fix kirin section mismatch warning (Nathan Chancellor)

 - Remove iproc PAXC slot check to allow VF support (Jitendra Bhivare)

 - Quirk Keystone K2G to limit MRRS to 256 (Kishon Vijay Abraham I)

 - Update Keystone to use MRRS quirk for host bridge instead of open
   coding (Kishon Vijay Abraham I)

 - Refactor Keystone link establishment (Kishon Vijay Abraham I)

 - Simplify and speed up Keystone link training (Kishon Vijay Abraham I)

 - Remove unused Keystone host_init argument (Kishon Vijay Abraham I)

 - Merge Keystone driver files into one (Kishon Vijay Abraham I)

 - Remove redundant Keystone platform_set_drvdata() (Kishon Vijay
   Abraham I)

 - Rename Keystone functions for uniformity (Kishon Vijay Abraham I)

 - Add Keystone device control module DT binding (Kishon Vijay Abraham
   I)

 - Use SYSCON API to get Keystone control module device IDs (Kishon
   Vijay Abraham I)

 - Clean up Keystone PHY handling (Kishon Vijay Abraham I)

 - Use runtime PM APIs to enable Keystone clock (Kishon Vijay Abraham I)

 - Clean up Keystone config space access checks (Kishon Vijay Abraham I)

 - Get Keystone outbound window count from DT (Kishon Vijay Abraham I)

 - Clean up Keystone outbound window configuration (Kishon Vijay Abraham
   I)

 - Clean up Keystone DBI setup (Kishon Vijay Abraham I)

 - Clean up Keystone ks_pcie_link_up() (Kishon Vijay Abraham I)

 - Fix Keystone IRQ status checking (Kishon Vijay Abraham I)

 - Add debug messages for all Keystone errors (Kishon Vijay Abraham I)

 - Clean up Keystone includes and macros (Kishon Vijay Abraham I)

 - Fix Mediatek unchecked return value from devm_pci_remap_iospace()
   (Gustavo A. R. Silva)

 - Fix Mediatek endpoint/port matching logic (Honghui Zhang)

 - Change Mediatek Root Port Class Code to PCI_CLASS_BRIDGE_PCI (Honghui
   Zhang)

 - Remove redundant Mediatek PM domain check (Honghui Zhang)

 - Convert Mediatek to pci_host_probe() (Honghui Zhang)

 - Fix Mediatek MSI enablement (Honghui Zhang)

 - Add Mediatek system PM support for MT2712 and MT7622 (Honghui Zhang)

 - Add Mediatek loadable module support (Honghui Zhang)

 - Detach VMD resources after stopping root bus to prevent orphan
   resources (Jon Derrick)

 - Convert pcitest build process to that used by other tools (iio, perf,
   etc) (Gustavo Pimentel)

* tag 'pci-v4.20-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci: (140 commits)
  PCI/AER: Refactor error injection fallbacks
  PCI/AER: Abstract AER interrupt handling
  PCI/AER: Reuse existing pcie_port_find_device() interface
  PCI/AER: Use managed resource allocations
  PCI: pcie: Remove redundant 'default n' from Kconfig
  PCI: aardvark: Implement emulated root PCI bridge config space
  PCI: mvebu: Convert to PCI emulated bridge config space
  PCI: mvebu: Drop unused PCI express capability code
  PCI: Introduce PCI bridge emulated config space common logic
  PCI: vmd: Detach resources after stopping root bus
  nvmet: Optionally use PCI P2P memory
  nvmet: Introduce helper functions to allocate and free request SGLs
  nvme-pci: Add support for P2P memory in requests
  nvme-pci: Use PCI p2pmem subsystem to manage the CMB
  IB/core: Ensure we map P2P memory correctly in rdma_rw_ctx_[init|destroy]()
  block: Add PCI P2P flag for request queue
  PCI/P2PDMA: Add P2P DMA driver writer's documentation
  docs-rst: Add a new directory for PCI documentation
  PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers
  PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset
  ...

Documentation/ABI/testing/sysfs-bus-pci

@@ -323,3 +323,27 @@ Description:
 
 		This is similar to /sys/bus/pci/drivers_autoprobe, but
 		affects only the VFs associated with a specific PF.
+
+What:		/sys/bus/pci/devices/.../p2pmem/size
+Date:		November 2017
+Contact:	Logan Gunthorpe <[email protected]>
+Description:
+		If the device has any Peer-to-Peer memory registered, this
+	        file contains the total amount of memory that the device
+		provides (in decimal).
+
+What:		/sys/bus/pci/devices/.../p2pmem/available
+Date:		November 2017
+Contact:	Logan Gunthorpe <[email protected]>
+Description:
+		If the device has any Peer-to-Peer memory registered, this
+	        file contains the amount of memory that has not been
+		allocated (in decimal).
+
+What:		/sys/bus/pci/devices/.../p2pmem/published
+Date:		November 2017
+Contact:	Logan Gunthorpe <[email protected]>
+Description:
+		If the device has any Peer-to-Peer memory registered, this
+	        file contains a '1' if the memory has been published for
+		use outside the driver that owns the device.

Documentation/PCI/endpoint/pci-test-howto.txt

@@ -99,17 +99,20 @@ Note that the devices listed here correspond to the value populated in 1.4 above
 2.2 Using Endpoint Test function Device
 
 pcitest.sh added in tools/pci/ can be used to run all the default PCI endpoint
-tests. Before pcitest.sh can be used pcitest.c should be compiled using the
-following commands.
+tests. To compile this tool the following commands should be used:
 
-	cd <kernel-dir>
-	make headers_install ARCH=arm
-	arm-linux-gnueabihf-gcc -Iusr/include tools/pci/pcitest.c -o pcitest
-	cp pcitest  <rootfs>/usr/sbin/
-	cp tools/pci/pcitest.sh <rootfs>
+	# cd <kernel-dir>
+	# make -C tools/pci
+
+or if you desire to compile and install in your system:
+
+	# cd <kernel-dir>
+	# make -C tools/pci install
+
+The tool and script will be located in <rootfs>/usr/bin/
 
 2.2.1 pcitest.sh Output
-	# ./pcitest.sh
+	# pcitest.sh
 	BAR tests
 
 	BAR0:           OKAY

Documentation/PCI/pci-error-recovery.txt

@@ -110,7 +110,7 @@ The actual steps taken by a platform to recover from a PCI error
 event will be platform-dependent, but will follow the general
 sequence described below.
 
-STEP 0: Error Event: ERR_NONFATAL
+STEP 0: Error Event
 -------------------
 A PCI bus error is detected by the PCI hardware.  On powerpc, the slot
 is isolated, in that all I/O is blocked: all reads return 0xffffffff,
@@ -228,7 +228,13 @@ proceeds to either STEP3 (Link Reset) or to STEP 5 (Resume Operations).
 If any driver returned PCI_ERS_RESULT_NEED_RESET, then the platform
 proceeds to STEP 4 (Slot Reset)
 
-STEP 3: Slot Reset
+STEP 3: Link Reset
+------------------
+The platform resets the link.  This is a PCI-Express specific step
+and is done whenever a fatal error has been detected that can be
+"solved" by resetting the link.
+
+STEP 4: Slot Reset
 ------------------
 
 In response to a return value of PCI_ERS_RESULT_NEED_RESET, the
@@ -314,7 +320,7 @@ Failure).
 >>> However, it probably should.
 
 
-STEP 4: Resume Operations
+STEP 5: Resume Operations
 -------------------------
 The platform will call the resume() callback on all affected device
 drivers if all drivers on the segment have returned
@@ -326,7 +332,7 @@ a result code.
 At this point, if a new error happens, the platform will restart
 a new error recovery sequence.
 
-STEP 5: Permanent Failure
+STEP 6: Permanent Failure
 -------------------------
 A "permanent failure" has occurred, and the platform cannot recover
 the device.  The platform will call error_detected() with a
@@ -349,27 +355,6 @@ errors. See the discussion in powerpc/eeh-pci-error-recovery.txt
 for additional detail on real-life experience of the causes of
 software errors.
 
-STEP 0: Error Event: ERR_FATAL
--------------------
-PCI bus error is detected by the PCI hardware. On powerpc, the slot is
-isolated, in that all I/O is blocked: all reads return 0xffffffff, all
-writes are ignored.
-
-STEP 1: Remove devices
---------------------
-Platform removes the devices depending on the error agent, it could be
-this port for all subordinates or upstream component (likely downstream
-port)
-
-STEP 2: Reset link
---------------------
-The platform resets the link.  This is a PCI-Express specific step and is
-done whenever a fatal error has been detected that can be "solved" by
-resetting the link.
-
-STEP 3: Re-enumerate the devices
---------------------
-Initiates the re-enumeration.
 
 Conclusion; General Remarks
 ---------------------------

Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt

@@ -50,6 +50,7 @@ Additional required properties for imx7d-pcie:
 - reset-names: Must contain the following entires:
 	       - "pciephy"
 	       - "apps"
+	       - "turnoff"
 
 Example:
 

Documentation/devicetree/bindings/pci/pci-keystone.txt

@@ -19,6 +19,9 @@ pcie_msi_intc : Interrupt controller device node for MSI IRQ chip
 	interrupt-cells: should be set to 1
 	interrupts: GIC interrupt lines connected to PCI MSI interrupt lines
 
+ti,syscon-pcie-id : phandle to the device control module required to set device
+		    id and vendor id.
+
  Example:
 	pcie_msi_intc: msi-interrupt-controller {
 			interrupt-controller;

Documentation/devicetree/bindings/pci/pci-rcar-gen2.txt

@@ -7,6 +7,7 @@ OHCI and EHCI controllers.
 
 Required properties:
 - compatible: "renesas,pci-r8a7743" for the R8A7743 SoC;
+	      "renesas,pci-r8a7744" for the R8A7744 SoC;
 	      "renesas,pci-r8a7745" for the R8A7745 SoC;
 	      "renesas,pci-r8a7790" for the R8A7790 SoC;
 	      "renesas,pci-r8a7791" for the R8A7791 SoC;

Documentation/devicetree/bindings/pci/rcar-pci.txt

@@ -2,13 +2,15 @@
 
 Required properties:
 compatible: "renesas,pcie-r8a7743" for the R8A7743 SoC;
+	    "renesas,pcie-r8a7744" for the R8A7744 SoC;
 	    "renesas,pcie-r8a7779" for the R8A7779 SoC;
 	    "renesas,pcie-r8a7790" for the R8A7790 SoC;
 	    "renesas,pcie-r8a7791" for the R8A7791 SoC;
 	    "renesas,pcie-r8a7793" for the R8A7793 SoC;
 	    "renesas,pcie-r8a7795" for the R8A7795 SoC;
 	    "renesas,pcie-r8a7796" for the R8A7796 SoC;
 	    "renesas,pcie-r8a77980" for the R8A77980 SoC;
+	    "renesas,pcie-r8a77990" for the R8A77990 SoC;
 	    "renesas,pcie-rcar-gen2" for a generic R-Car Gen2 or
 				     RZ/G1 compatible device.
 	    "renesas,pcie-rcar-gen3" for a generic R-Car Gen3 compatible device.

Documentation/devicetree/bindings/pci/ti-pci.txt

@@ -26,6 +26,11 @@ HOST MODE
    ranges,
    interrupt-map-mask,
    interrupt-map : as specified in ../designware-pcie.txt
+ - ti,syscon-unaligned-access: phandle to the syscon DT node. The 1st argument
+			       should contain the register offset within syscon
+			       and the 2nd argument should contain the bit field
+			       for setting the bit to enable unaligned
+			       access.
 
 DEVICE MODE
 ===========

Documentation/driver-api/index.rst

@@ -30,7 +30,7 @@ available subsections can be seen below.
    input
    usb/index
    firewire
-   pci
+   pci/index
    spi
    i2c
    hsi

Documentation/driver-api/pci/index.rst

@@ -0,0 +1,22 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================================
+The Linux PCI driver implementer's API guide
+============================================
+
+.. class:: toc-title
+
+	   Table of contents
+
+.. toctree::
+   :maxdepth: 2
+
+   pci
+   p2pdma
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/pci/p2pdma.rst

@@ -0,0 +1,145 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+PCI Peer-to-Peer DMA Support
+============================
+
+The PCI bus has pretty decent support for performing DMA transfers
+between two devices on the bus. This type of transaction is henceforth
+called Peer-to-Peer (or P2P). However, there are a number of issues that
+make P2P transactions tricky to do in a perfectly safe way.
+
+One of the biggest issues is that PCI doesn't require forwarding
+transactions between hierarchy domains, and in PCIe, each Root Port
+defines a separate hierarchy domain. To make things worse, there is no
+simple way to determine if a given Root Complex supports this or not.
+(See PCIe r4.0, sec 1.3.1). Therefore, as of this writing, the kernel
+only supports doing P2P when the endpoints involved are all behind the
+same PCI bridge, as such devices are all in the same PCI hierarchy
+domain, and the spec guarantees that all transactions within the
+hierarchy will be routable, but it does not require routing
+between hierarchies.
+
+The second issue is that to make use of existing interfaces in Linux,
+memory that is used for P2P transactions needs to be backed by struct
+pages. However, PCI BARs are not typically cache coherent so there are
+a few corner case gotchas with these pages so developers need to
+be careful about what they do with them.
+
+
+Driver Writer's Guide
+=====================
+
+In a given P2P implementation there may be three or more different
+types of kernel drivers in play:
+
+* Provider - A driver which provides or publishes P2P resources like
+  memory or doorbell registers to other drivers.
+* Client - A driver which makes use of a resource by setting up a
+  DMA transaction to or from it.
+* Orchestrator - A driver which orchestrates the flow of data between
+  clients and providers.
+
+In many cases there could be overlap between these three types (i.e.,
+it may be typical for a driver to be both a provider and a client).
+
+For example, in the NVMe Target Copy Offload implementation:
+
+* The NVMe PCI driver is both a client, provider and orchestrator
+  in that it exposes any CMB (Controller Memory Buffer) as a P2P memory
+  resource (provider), it accepts P2P memory pages as buffers in requests
+  to be used directly (client) and it can also make use of the CMB as
+  submission queue entries (orchastrator).
+* The RDMA driver is a client in this arrangement so that an RNIC
+  can DMA directly to the memory exposed by the NVMe device.
+* The NVMe Target driver (nvmet) can orchestrate the data from the RNIC
+  to the P2P memory (CMB) and then to the NVMe device (and vice versa).
+
+This is currently the only arrangement supported by the kernel but
+one could imagine slight tweaks to this that would allow for the same
+functionality. For example, if a specific RNIC added a BAR with some
+memory behind it, its driver could add support as a P2P provider and
+then the NVMe Target could use the RNIC's memory instead of the CMB
+in cases where the NVMe cards in use do not have CMB support.
+
+
+Provider Drivers
+----------------
+
+A provider simply needs to register a BAR (or a portion of a BAR)
+as a P2P DMA resource using :c:func:`pci_p2pdma_add_resource()`.
+This will register struct pages for all the specified memory.
+
+After that it may optionally publish all of its resources as
+P2P memory using :c:func:`pci_p2pmem_publish()`. This will allow
+any orchestrator drivers to find and use the memory. When marked in
+this way, the resource must be regular memory with no side effects.
+
+For the time being this is fairly rudimentary in that all resources
+are typically going to be P2P memory. Future work will likely expand
+this to include other types of resources like doorbells.
+
+
+Client Drivers
+--------------
+
+A client driver typically only has to conditionally change its DMA map
+routine to use the mapping function :c:func:`pci_p2pdma_map_sg()` instead
+of the usual :c:func:`dma_map_sg()` function. Memory mapped in this
+way does not need to be unmapped.
+
+The client may also, optionally, make use of
+:c:func:`is_pci_p2pdma_page()` to determine when to use the P2P mapping
+functions and when to use the regular mapping functions. In some
+situations, it may be more appropriate to use a flag to indicate a
+given request is P2P memory and map appropriately. It is important to
+ensure that struct pages that back P2P memory stay out of code that
+does not have support for them as other code may treat the pages as
+regular memory which may not be appropriate.
+
+
+Orchestrator Drivers
+--------------------
+
+The first task an orchestrator driver must do is compile a list of
+all client devices that will be involved in a given transaction. For
+example, the NVMe Target driver creates a list including the namespace
+block device and the RNIC in use. If the orchestrator has access to
+a specific P2P provider to use it may check compatibility using
+:c:func:`pci_p2pdma_distance()` otherwise it may find a memory provider
+that's compatible with all clients using  :c:func:`pci_p2pmem_find()`.
+If more than one provider is supported, the one nearest to all the clients will
+be chosen first. If more than one provider is an equal distance away, the
+one returned will be chosen at random (it is not an arbitrary but
+truely random). This function returns the PCI device to use for the provider
+with a reference taken and therefore when it's no longer needed it should be
+returned with pci_dev_put().
+
+Once a provider is selected, the orchestrator can then use
+:c:func:`pci_alloc_p2pmem()` and :c:func:`pci_free_p2pmem()` to
+allocate P2P memory from the provider. :c:func:`pci_p2pmem_alloc_sgl()`
+and :c:func:`pci_p2pmem_free_sgl()` are convenience functions for
+allocating scatter-gather lists with P2P memory.
+
+Struct Page Caveats
+-------------------
+
+Driver writers should be very careful about not passing these special
+struct pages to code that isn't prepared for it. At this time, the kernel
+interfaces do not have any checks for ensuring this. This obviously
+precludes passing these pages to userspace.
+
+P2P memory is also technically IO memory but should never have any side
+effects behind it. Thus, the order of loads and stores should not be important
+and ioreadX(), iowriteX() and friends should not be necessary.
+However, as the memory is not cache coherent, if access ever needs to
+be protected by a spinlock then :c:func:`mmiowb()` must be used before
+unlocking the lock. (See ACQUIRES VS I/O ACCESSES in
+Documentation/memory-barriers.txt)
+
+
+P2P DMA Support Library
+=======================
+
+.. kernel-doc:: drivers/pci/p2pdma.c
+   :export: