ACPI 6.2 adds support for named methods to access the label storage area
of an NVDIMM. We prefer these new methods if available and otherwise
fallback to the NVDIMM_FAMILY_INTEL _DSMs. The kernel ioctls,
ND_IOCTL_{GET,SET}_CONFIG_{SIZE,DATA}, remain generic and the driver
translates the 'package' payloads into the NVDIMM_FAMILY_INTEL 'buffer'
format to maintain compatibility with existing userspace and keep the
output buffer parsing code in the driver common.

The output payloads are mostly compatible save for the 'label area
locked' status that moves from the 'config_size' (_LSI) command to the
'config_read' (_LSR) command status.

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Though nfit_test need to show what feature is supported via ND_CMD_CALL on
device/nfit/dsm_mask, currently there is no way to tell it.
This patch makes to enable it.
Signed-off-by: NYasunori Goto <y-goto@jp.fujitsu.com>
Reviewed-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

ACPI 6.2 defines in section 9.20.7.2 that the OSPM may call a Start
ARS with Flags Bit [1] set upon receiving the 0x81 notification.

  Upon receiving the notification, the OSPM may decide to issue
  a Start ARS with Flags Bit [1] set to prepare for the retrieval
  of existing records and issue the Query ARS Status function to
  retrieve the records.

Add support to call a Start ARS from acpi_nfit_uc_error_notify()
with ND_ARS_RETURN_PREV_DATA set when HW_ERROR_SCRUB_ON is not set.

Link: http://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdfSigned-off-by: NToshi Kani <toshi.kani@hpe.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Linda Knippers <linda.knippers@hpe.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

ACPI 6.2 defines a new ACPI notification value to NVDIMM Root Device
in Table 5-169.

 0x81 Unconsumed Uncorrectable Memory Error Detected
      Used to pro-actively notify OSPM of uncorrectable memory errors
      detected (for example a memory scrubbing engine that continuously
      scans the NVDIMMs memory). This is an optional notification. Only
      locations that were mapped in to SPA by the platform will generate
      a notification.

Add support of this notification value by initiating an ARS scan. This
will find new error locations and add their badblocks information.

Link: http://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdfSigned-off-by: NToshi Kani <toshi.kani@hpe.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Linda Knippers <linda.knippers@hpe.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

There are new types and helpers that are supposed to be used in new code.

As a preparation to get rid of legacy types and API functions do
the conversion here.
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

The workqueue may still be running when the devres callbacks start
firing to deallocate an acpi_nfit_desc instance. Stop and flush the
workqueue before letting any other devres de-allocations proceed.
Reported-by: NLinda Knippers <linda.knippers@hpe.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The nvdimm probe flushing mechanism gives userspace a sync point where
it knows all asynchronous driver probe sequences have completed.
However, it need not wait for other asynchronous actions, like
on-demand address-range-scrub. Track the init work separately from other
work in the workqueue, and only flush the former.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Stop requiring dimms be successfully mapped into a
system-physical-address range. For provisioning and hardware remediation
purposes the kernel should account for failed devices in sysfs. If
possible it should still allow management commands to be sent to the
device.
Reported-by: NToshi Kani <toshi.kani@hpe.com>
Tested-by: NToshi Kani <toshi.kani@hpe.com>
Reported-by: NLinda Knippers <linda.knippers@hpe.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

A recent flurry of bug discoveries in the nfit driver's DSM marshalling
routine has highlighted the fact that we do not have unit test coverage
for this routine. Add a self-test of acpi_nfit_ctl() routine before
probing the "nfit_test.0" device. This mocks stimulus to acpi_nfit_ctl()
and if any of the tests fail "nfit_test.0" will be unavailable causing
the rest of the tests to not run / fail.

This unit test will also be a place to land reproductions of quirky BIOS
behavior discovered in the field and ensure the kernel does not regress
against implementations it has seen in practice.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Starting a full Address Range Scrub (ARS) on hitting a memory error
machine check exception may not always be desirable. Provide a way
through sysfs 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.

Cc: linux-acpi@vger.kernel.org
Cc: Linda Knippers <linda.knippers@hpe.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Trigger an nmemX/nfit/flags attribute to fire an event whenever a
smart-threshold DSM is received.
Reviewed-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NRafael J. Wysocki <rafael@kernel.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Per "ACPI 6.1 Section 9.20.3" NVDIMM devices, children of the ACPI0012
NVDIMM Root device, can receive health event notifications.

Given that these devices are precluded from registering a notification
handler via acpi_driver.acpi_device_ops (due to no _HID), we use
acpi_install_notify_handler() directly.  The registered handler,
acpi_nvdimm_notify(), triggers a poll(2) event on the nmemX/nfit/flags
sysfs attribute when a health event notification is received.

Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: NToshi Kani <toshi.kani@hpe.com>
Reviewed-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NRafael J. Wysocki <rafael@kernel.org>
Reviewed-by: NToshi Kani <toshi.kani@hpe.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

We have had a couple bugs in this implementation in the past and before
we add another ->notify() implementation for nvdimm devices, lets allow
this routine to be exercised via nfit_test.

Rewrite acpi_nfit_notify() in terms of a generic struct device and
acpi_handle parameter, and then implement a mock acpi_evaluate_object()
that returns a _FIT payload.

Cc: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NRafael J. Wysocki <rafael@kernel.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Commit 20985164 "acpi: nfit: Add support for hot-add" added
support for _FIT notifications, but it neglected to verify the
notification event code matches the one in the ACPI spec for
"NFIT Update". Currently there is only one code in the spec, but
once additional codes are added, older kernels (without this fix)
will misbehave by assuming all event notifications are for an
NFIT Update.

Fixes: 20985164 ("acpi: nfit: Add support for hot-add")
Cc: <stable@vger.kernel.org>
Cc: <linux-acpi@vger.kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Reported-by: NLinda Knippers <linda.knippers@hpe.com>
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

When a latent (unknown to 'badblocks') error is encountered, it will
trigger a machine check exception. On a system with machine check
recovery, this will only SIGBUS the process(es) which had the bad page
mapped (as opposed to a kernel panic on platforms without machine
check recovery features). In the former case, we want to trigger a full
rescan of that nvdimm bus. This will allow any additional, new errors
to be captured in the block devices' badblocks lists, and offending
operations on them can be trapped early, avoiding machine checks.

This is done by registering a callback function with the
x86_mce_decoder_chain and calling the new ars_rescan functionality with
the address in the mce notificatiion.

Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

With the arrival of x86-machine-check support the nfit driver will add a
(conditionally-compiled) source file.  Prepare for this by moving all
nfit source to drivers/acpi/nfit/.  This is pure code movement, no
functional changes.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Normally, an ARS (Address Range Scrub) only happens at
boot/initialization time. There can however arise situations where a
bus-wide rescan is needed - notably, in the case of discovering a latent
media error, we should do a full rescan to figure out what other sectors
are bad, and thus potentially avoid triggering an mce on them in the
future. Also provide a sysfs trigger to start a bus-wide scrub.

Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Pass the nfit buffer as a parameter rather than hanging it off of
acpi_desc.
Reviewed-by: N"Lee, Chun-Yi" <jlee@suse.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

acpi_evaluate_object() allocates memory. Free the buffer allocated
during acpi_nfit_add(). In order for this memory to be freed
acpi_nfit_init() needs to be converted to duplicate the nfit contents in
its internal allocation.  Use zero-length arrays to minimize the thrash
with the rest of the nfit driver implementation.

All of the add_<nfit-sub-table>() routines now validate a minimum table
size and expect hotplugged tables to match the size of the original
table to count as a duplicate. For variable length tables, like 'idt'
and 'flush', we calculate the dynamic size. Note that hotplug by
definition cannot change the interleave as it would cause data
corruption of in-use namespaces.

Cc: Vishal Verma <vishal.l.verma@intel.com>
Reported-by: NXiao Guangrong <guangrong.xiao@intel.com>
Reported-by: NHaozhong Zhang <haozhong.zhang@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The __pmem address space was meant to annotate codepaths that touch
persistent memory and need to coordinate a call to wmb_pmem().  Now that
wmb_pmem() is gone, there is little need to keep this annotation.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

nvdimm_flush() is a replacement for the x86 'pcommit' instruction.  It is
an optional write flushing mechanism that an nvdimm bus can provide for
the pmem driver to consume.  In the case of the NFIT nvdimm-bus-provider
nvdimm_flush() is implemented as a series of flush-hint-address [1]
writes to each dimm in the interleave set (region) that backs the
namespace.

The nvdimm_has_flush() routine relies on platform firmware to describe
the flushing capabilities of a platform.  It uses the heuristic of
whether an nvdimm bus provider provides flush address data to return a
ternary result:

      1: flush addresses defined
      0: dimm topology described without flush addresses (assume ADR)
 -errno: no topology information, unable to determine flush mechanism

The pmem driver is expected to take the following actions on this ternary
result:

      1: nvdimm_flush() in response to REQ_FUA / REQ_FLUSH and shutdown
      0: do not set, WC or FUA on the queue, take no further action
 -errno: warn and then operate as if nvdimm_has_flush() returned '0'

The caveat of this heuristic is that it can not distinguish the "dimm
does not have flush address" case from the "platform firmware is broken
and failed to describe a flush address".  Given we are already
explicitly trusting the NFIT there's not much more we can do beyond
blacklisting broken firmwares if they are ever encountered.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

In preparation for triggering flushes of a DIMM's writes-posted-queue
(WPQ) via the pmem driver move mapping of flush hint addresses to the
region driver.  Since this uses devm_nvdimm_memremap() the flush
addresses will remain mapped while any region to which the dimm belongs
is active.

We need to communicate more information to the nvdimm core to facilitate
this mapping, namely each dimm object now carries an array of flush hint
address resources.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Now that all shared mappings are handled by devm_nvdimm_memremap() we no
longer need nfit_spa_map() nor do we need to trigger a callback to the
bus provider at region disable time.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Per JEDEC Annex L Release 3 the SPD data is:

Bits 9~5 00 000 = Function Undefined
         00 001 = Byte addressable energy backed
         00 010 = Block addressed
         00 011 = Byte addressable, no energy backed
         All other codes reserved
Bits 4~0 0 0000 = Proprietary interface
         0 0001 = Standard interface 1
         All other codes reserved; see Definitions of Functions

...and per the ACPI 6.1 spec:

    byte0: Bits 4~0 (0 or 1)
    byte1: Bits 9~5 (1, 2, or 3)

...so a format interface code displayed as 0x301 should be stored in the
nfit as (0x1, 0x3), little-endian.

Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Robert Moore <robert.moore@intel.com>
Cc: Robert Elliott <elliott@hpe.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=121161
Fixes: 30ec5fd4 ("nfit: fix format interface code byte order per ACPI6.1")
Fixes: 5ad9a7fd ("acpi/nfit: Update nfit driver to comply with ACPI 6.1")
Reported-by: NKristin Jacque <kristin.jacque@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Add the Microsoft _DSM command set to the white list of NVDIMM command
sets.

This command set is documented at:

    https://msdn.microsoft.com/library/windows/hardware/mt604741

Cc: Pavel Machek <pavel@ucw.cz>
[pavel: fix up braces]
Signed-off-by: NStuart Hayes <stuart.w.hayes@gmail.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

ACPI6.1 clarifies that DCR fields are stored as an array of bytes,
update the format interface code constants to match.
Reviewed-by: NToshi Kani <toshi.kani@hpe.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

There are currently 4 known similar but incompatible definitions of the
command sets that can be sent to an NVDIMM through ACPI.  It is also
clear that future platform generations (ACPI or not) will continue to
revise and extend the DIMM command set as new devices and use cases
arrive.

It is obviously untenable to continue to proliferate divergence
of these command definitions, and to that end a standardization process
has begun to provide for a unified specification.  However, that leaves a
problem about what to do with this first generation where vendors are
already shipping divergence.

The Linux kernel can support these initial diverged platforms without
giving platform-firmware free reign to continue to diverge and compound
kernel maintenance overhead.  The kernel implementation can encourage
standardization in two ways:

1/ Require that any function code that userspace wants to send be
   explicitly white-listed in the implementation.  For ACPI this means
   function codes marked as supported by acpi_check_dsm() may
   only be invoked if they appear in the white-list.  A function must be
   publicly documented before it is added to the white-list.

2/ The above restrictions can be trivially bypassed by using the
   "vendor-specific" payload command.  However, since vendor-specific
   commands are by definition not publicly documented and have the
   potential to corrupt the kernel's view of the dimm state, we provide a
   toggle to disable vendor-specific operations.  Enabling undefined
   behavior is a policy decision that can be made by the platform owner
   and encourages firmware implementations to choose public over
   private command implementations.

Based on an initial patch from Jerry Hoemann
Cc: Jerry Hoemann <jerry.hoemann@hpe.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Clarify the distinction between "commands", the ioctls userspace calls
to request the kernel take some action on a given dimm device, and
"_DSMs", the actual function numbers used in the firmware interface to
the DIMM.  _DSMs are ACPI specific whereas commands are Linux kernel
generic.

This is in preparation for breaking the 1:1 implicit relationship
between the kernel ioctl number space and the firmware specific function
numbers.

Cc: Jerry Hoemann <jerry.hoemann@hpe.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Starting with ACPI 6.1 an NFIT table will report multiple 'NVDIMM
Control Region Structure' instances per-dimm, one for each supported
format interface.  Report that code in the following format in sysfs:

    nmemX/nfit/formats
    nmemX/nfit/format
    nmemX/nfit/format1
    nmemX/nfit/format2
    ...
    nmemX/nfit/formatN

Where format2 - formatN are theoretical as there are no known DIMMs with
support for more than two interface formats.

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.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Address range scrub is a potentially long running process that we want
to complete before any pmem regions are registered.  Perform this
operation asynchronously to allow other drivers to load in the meantime.

Platform firmware may have initiated a partial scrub prior to the driver
loading, so we must be careful to consume those results before kicking
off kernel initiated scrubs on other regions.

This rework also makes the registration path more tolerant of scrub
errors in that it splits scrubbing into 2 phases.  The first phase
synchronously waits for a platform-firmware initiated scrub to complete.
The second phase scans the remaining address ranges asynchronously and
notifies the related driver(s) when the scrub completes.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Introduce a workqueue that will be used to run address range scrub
asynchronously with the rest of nvdimm device probing.

Userspace still wants notification when probing operations complete, so
introduce a new callback to flush this workqueue when userspace is
awaiting probe completion.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The nvdimm unit test infrastructure performs its own initialization of
an acpi_nfit_desc to specify test overrides over the native
implementation.  Make it clear which attributes and operations it is
overriding by re-using acpi_nfit_init_desc() as a common starting point.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

The return value from an 'ndctl_fn' reports the command execution
status, i.e. was the command properly formatted and was it successfully
submitted to the bus provider.  The new 'cmd_rc' parameter allows the bus
provider to communicate command specific results, translated into
common error codes.

Convert the ARS commands to this scheme to:

1/ Consolidate status reporting

2/ Prepare for for expanding ars unit test cases

3/ Make the implementation more generic

Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

ACPI 6.1 and JEDEC Annex L Release 3 formalize the format interface
code.  Add definitions and update their usage in the unit test.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

When support for _FIT was added, the code presumed that the data
returned by the _FIT method is identical to the NFIT table, which
starts with an acpi_table_header.  However, the _FIT is defined
to return a data in the format of a series of NFIT type structure
entries and as a method, has an acpi_object header rather tahn
an acpi_table_header.

To address the differences, explicitly save the acpi_table_header
from the NFIT, since it is accessible through /sys, and change
the nfit pointer in the acpi_desc structure to point to the
table entries rather than the headers.

Reported-by: Jeff Moyer (jmoyer@redhat.com>
Signed-off-by: NLinda Knippers <linda.knippers@hpe.com>
Acked-by: NVishal Verma <vishal.l.verma@intel.com>
[vishal: fix up unit test for new header assumptions]
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Add a .notify callback to the acpi_nfit_driver that gets called on a
hotplug event. From this, evaluate the _FIT ACPI method which returns
the updated NFIT with handles for the hot-plugged NVDIMM.

Iterate over the new NFIT, and add any new tables found, and
register/enable the corresponding regions.

In the nfit test framework, after normal initialization, update the NFIT
with a new hot-plugged NVDIMM, and directly call into the driver to
update its view of the available regions.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Elliott, Robert <elliott@hpe.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: <linux-acpi@vger.kernel.org>
Cc: <linux-nvdimm@lists.01.org>
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

ACPICA commit 534deab97fb416a13bfede15c538e2c9eac9384a

Updated one of the memory subtable flags to clarify.

Link: https://github.com/acpica/acpica/commit/534deab9Signed-off-by: NBob Moore <robert.moore@intel.com>
Signed-off-by: NLv Zheng <lv.zheng@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

This should result in a pretty sizeable performance gain for reads.  For
rough comparison I did some simple read testing using PMEM to compare
reads of write combining (WC) mappings vs write-back (WB).  This was
done on a random lab machine.

PMEM reads from a write combining mapping:
	# dd of=/dev/null if=/dev/pmem0 bs=4096 count=100000
	100000+0 records in
	100000+0 records out
	409600000 bytes (410 MB) copied, 9.2855 s, 44.1 MB/s

PMEM reads from a write-back mapping:
	# dd of=/dev/null if=/dev/pmem0 bs=4096 count=1000000
	1000000+0 records in
	1000000+0 records out
	4096000000 bytes (4.1 GB) copied, 3.44034 s, 1.2 GB/s

To be able to safely support a write-back aperture I needed to add
support for the "read flush" _DSM flag, as outlined in the DSM spec:

http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf

This flag tells the ND BLK driver that it needs to flush the cache lines
associated with the aperture after the aperture is moved but before any
new data is read.  This ensures that any stale cache lines from the
previous contents of the aperture will be discarded from the processor
cache, and the new data will be read properly from the DIMM.  We know
that the cache lines are clean and will be discarded without any
writeback because either a) the previous aperture operation was a read,
and we never modified the contents of the aperture, or b) the previous
aperture operation was a write and we must have written back the dirtied
contents of the aperture to the DIMM before the I/O was completed.

In order to add support for the "read flush" flag I needed to add a
generic routine to invalidate cache lines, mmio_flush_range().  This is
protected by the ARCH_HAS_MMIO_FLUSH Kconfig variable, and is currently
only supported on x86.
Signed-off-by: NRoss Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Add support for the three ARS DSM commands:
- Query ARS Capabilities - Queries the firmware to check if a given
  range supports scrub, and if so, which type (persistent vs. volatile)
- Start ARS - Starts a scrub for a given range/type
- Query ARS Status - Checks status of a previously started scrub, and
  provides the error logs if any.

  The commands are described by the example DSM spec at:
  http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf

Also add these commands to the nfit_test test framework, and return
canned data.
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Add support in the NFIT BLK I/O path for the "latch" flag
defined in the "Get Block NVDIMM Flags" _DSM function:

http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf

This flag requires the driver to read back the command register after it
is written in the block I/O path.  This ensures that the hardware has
fully processed the new command and moved the aperture appropriately.
Signed-off-by: NRoss Zwisler <ross.zwisler@linux.intel.com>
Acked-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>