[PATCH 3/3] nfit: add support for NVDIMM "latch" flag

[Ross Zwisler <ross.zwisler@linux.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: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: linux-nvdimm@lists.01.org
Cc: linux-acpi@vger.kernel.org
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Toshi Kani <toshi.kani@hp.com>
---
 drivers/acpi/nfit.c | 33 ++++++++++++++++++++++++++++++++-
 drivers/acpi/nfit.h |  6 ++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
index b3c446412f61..9062c11c1062 100644
--- a/drivers/acpi/nfit.c
+++ b/drivers/acpi/nfit.c
@@ -1059,7 +1059,9 @@ static void write_blk_ctl(struct nfit_blk *nfit_blk, unsigned int bw,
 
 	writeq(cmd, mmio->base + offset);
 	wmb_blk(nfit_blk);
-	/* FIXME: conditionally perform read-back if mandated by firmware */
+
+	if (nfit_blk->dimm_flags & ND_BLK_DCR_LATCH)
+		readq(mmio->base + offset);
 }
 
 static int acpi_nfit_blk_single_io(struct nfit_blk *nfit_blk,
@@ -1258,6 +1260,28 @@ static int nfit_blk_init_interleave(struct nfit_blk_mmio *mmio,
 	return 0;
 }
 
+static int acpi_nfit_blk_get_flags(struct nvdimm_bus_descriptor *nd_desc,
+		struct nvdimm *nvdimm, struct nfit_blk *nfit_blk)
+{
+	struct nd_cmd_dimm_flags flags;
+	int rc;
+
+	memset(&flags, 0, sizeof(flags));
+	rc = nd_desc->ndctl(nd_desc, nvdimm, ND_CMD_DIMM_FLAGS, &flags,
+			sizeof(flags));
+
+	if (rc >= 0) {
+		if (!flags.status)
+			nfit_blk->dimm_flags = flags.flags;
+		else if (flags.status == ND_DSM_STATUS_NOT_SUPPORTED)
+			nfit_blk->dimm_flags = 0; /* as per the _DSM spec */
+		else
+			rc = -EINVAL;
+	}
+
+	return rc;
+}
+
 static int acpi_nfit_blk_region_enable(struct nvdimm_bus *nvdimm_bus,
 		struct device *dev)
 {
@@ -1333,6 +1357,13 @@ static int acpi_nfit_blk_region_enable(struct nvdimm_bus *nvdimm_bus,
 		return rc;
 	}
 
+	rc = acpi_nfit_blk_get_flags(nd_desc, nvdimm, nfit_blk);
+	if (rc < 0) {
+		dev_dbg(dev, "%s: %s failed get DIMM flags\n",
+				__func__, nvdimm_name(nvdimm));
+		return rc;
+	}
+
 	nfit_flush = nfit_mem->nfit_flush;
 	if (nfit_flush && nfit_flush->flush->hint_count != 0) {
 		struct acpi_nfit_flush_address *flush = nfit_flush->flush;
diff --git a/drivers/acpi/nfit.h b/drivers/acpi/nfit.h
index d284729cc37c..98e36ca0dfc2 100644
--- a/drivers/acpi/nfit.h
+++ b/drivers/acpi/nfit.h
@@ -40,6 +40,11 @@ enum nfit_uuids {
 	NFIT_UUID_MAX,
 };
 
+enum {
+	ND_BLK_DCR_LATCH = 2,
+	ND_DSM_STATUS_NOT_SUPPORTED = 1,
+};
+
 struct nfit_spa {
 	struct acpi_nfit_system_address *spa;
 	struct list_head list;
@@ -131,6 +136,7 @@ struct nfit_blk {
 	u64 stat_offset;
 	u64 cmd_offset;
 	void __iomem *nvdimm_flush;
+	u32 dimm_flags;
 };
 
 struct nfit_spa_mapping {
-- 
1.9.3