This is an attempt to document the nfit sysfs interface. The
descriptions have been collected from git commit logs and the ACPI
specification 6.2.

Signed-off-by: Aishwarya Pant <aishp...@gmail.com>
---
Changes in v2:
- Add descriptions for range_index and ecc_unit_size
- Edit various descriptions as suggested

 Documentation/ABI/testing/sysfs-bus-nfit | 233 +++++++++++++++++++++++++++++++
 1 file changed, 233 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-nfit

diff --git a/Documentation/ABI/testing/sysfs-bus-nfit 
b/Documentation/ABI/testing/sysfs-bus-nfit
new file mode 100644
index 000000000000..619eb8ca0f99
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-nfit
@@ -0,0 +1,233 @@
+For all of the nmem device attributes under nfit/*, see the 'NVDIMM Firmware
+Interface Table (NFIT)' section in the ACPI specification
+(http://www.uefi.org/specifications) for more details.
+
+What:          /sys/bus/nd/devices/nmemX/nfit/serial
+Date:          Jun, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Serial number of the NVDIMM (non-volatile dual in-line
+               memory module), assigned by the module vendor.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/handle
+Date:          Apr, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) The address (given by the _ADR object) of the device on its
+               parent bus of the NVDIMM device containing the NVDIMM region.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/device
+Date:          Apr, 2015
+KernelVersion: v4.1
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Device id for the NVDIMM, assigned by the module vendor.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/rev_id
+Date:          Jun, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Revision of the NVDIMM, assigned by the module vendor.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/phys_id
+Date:          Apr, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Handle (i.e., instance number) for the SMBIOS (system
+               management BIOS) Memory Device structure describing the NVDIMM
+               containing the NVDIMM region.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/flags
+Date:          Jun, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) The flags in the NFIT memory device sub-structure indicate
+               the state of the data on the nvdimm relative to its energy
+               source or last "flush to persistence".
+
+               The attribute is a translation of the 'NVDIMM State Flags' field
+               in section 5.2.25.3 'NVDIMM Region Mapping' Structure of the
+               ACPI specification 6.2.
+
+               The health states are "save_fail", "restore_fail", "flush_fail",
+               "not_armed", "smart_event", "map_fail" and "smart_notify".
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/format
+What:          /sys/bus/nd/devices/nmemX/nfit/format1
+What:          /sys/bus/nd/devices/nmemX/nfit/formats
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) The interface codes indicate support for persistent memory
+               mapped directly into system physical address space and / or a
+               block aperture access mechanism to the NVDIMM media.
+               The 'formats' attribute displays the number of supported
+               interfaces.
+
+               This layout is compatible with existing libndctl binaries that
+               only expect one code per-dimm as they will ignore
+               nmemX/nfit/formats and nmemX/nfit/formatN.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/vendor
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Vendor id of the NVDIMM.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/dsm_mask
+Date:          May, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) The bitmask indicates the supported device specific control
+               functions relative to the NVDIMM command family supported by the
+               device
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/family
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Displays the NVDIMM family command sets. Values
+               0, 1, 2 and 3 correspond to NVDIMM_FAMILY_INTEL,
+               NVDIMM_FAMILY_HPE1, NVDIMM_FAMILY_HPE2 and NVDIMM_FAMILY_MSFT
+               respectively.
+
+               See the specifications for these command families here:
+               http://pmem.io/documents/NVDIMM_DSM_Interface-V1.6.pdf
+               
https://github.com/HewlettPackard/hpe-nvm/blob/master/Documentation/
+               https://msdn.microsoft.com/library/windows/hardware/mt604741";
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/id
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) ACPI specification 6.2 section 5.2.25.9, defines an
+               identifier for an NVDIMM, which refelects the id attribute.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/subsystem_vendor
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Sub-system vendor id of the NVDIMM non-volatile memory
+               subsystem controller.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/subsystem_rev_id
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Sub-system revision id of the NVDIMM non-volatile memory 
subsystem
+               controller, assigned by the non-volatile memory subsystem
+               controller vendor.
+
+
+What:          /sys/bus/nd/devices/nmemX/nfit/subsystem_device
+Date:          Apr, 2016
+KernelVersion: v4.7
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Sub-system device id for the NVDIMM non-volatile memory
+               subsystem controller, assigned by the non-volatile memory
+               subsystem controller vendor.
+
+
+What:          /sys/bus/nd/devices/ndbusX/nfit/revision
+Date:          Jun, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) ACPI NFIT table revision number.
+
+
+What:          /sys/bus/nd/devices/ndbusX/nfit/scrub
+Date:          Sep, 2016
+KernelVersion: v4.9
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RW) This shows the number of full Address Range Scrubs (ARS)
+               that have been completed since driver load time. Userspace can
+               wait on this using select/poll etc. A '+' at the end indicates
+               an ARS is in progress
+
+               Writing a value of 1 triggers an ARS scan.
+
+
+What:          /sys/bus/nd/devices/ndbusX/nfit/hw_error_scrub
+Date:          Sep, 2016
+KernelVersion: v4.9
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RW) Provides a way to toggle the behavior between just adding
+               the address (cache line) where the MCE happened to the poison
+               list and doing a full scrub. The former (selective insertion of
+               the address) is done unconditionally.
+
+               This attribute can have the following values written to it:
+
+               '0': Switch to the default mode where an exception will only
+               insert the address of the memory error into the poison and
+               badblocks lists.
+               '1': Enable a full scrub to happen if an exception for a memory
+               error is received.
+
+
+What:          /sys/bus/nd/devices/ndbusX/nfit/dsm_mask
+Date:          Jun, 2017
+KernelVersion: v4.13
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) The bitmask indicates the supported bus specific control
+               functions. See the section named 'NVDIMM Root Device _DSMs' in
+               the ACPI specification.
+
+
+What:          /sys/bus/nd/devices/regionX/nfit/range_index
+Date:          Jun, 2015
+KernelVersion: v4.2
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) A unique number provided by the BIOS to identify an address
+               range. Used by NVDIMM Region Mapping Structure to uniquely refer
+               to this structure. Value of 0 is reserved and not used as an
+               index.
+
+
+What:          /sys/bus/nd/devices/regionX/nfit/ecc_unit_size
+Date:          Aug, 2017
+KernelVersion: v4.14
+Contact:       linux-nvdimm@lists.01.org
+Description:
+               (RO) Size of a write request to a DIMM that will not incur a
+               read-modify-write cycle at the memory controller.
+
+               When the nfit driver initializes it runs an ARS (Address Range
+               Scrub) operation across every pmem range. Part of that process
+               involves determining the ARS capabilities of a given address
+               range. One of the capabilities that is reported is the 'Clear
+               Uncorrectable Error Range Length Unit Size' (see: ACPI 6.2
+               section 9.20.7.4 Function Index 1 - Query ARS Capabilities).
+               This property indicates the boundary at which the NVDIMM may
+               need to perform read-modify-write cycles to maintain ECC (Error
+               Correcting Code) blocks.
-- 
2.16.2

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