nd_blk: change aperture mapping from WC to WB

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

3 files changed, 43 insertions, 29 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 114cf48085ab..4baeb853e0c3 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -410,6 +410,7 @@ config ACPI_NFIT
 	tristate "ACPI NVDIMM Firmware Interface Table (NFIT)"
 	depends on PHYS_ADDR_T_64BIT
 	depends on BLK_DEV
+	depends on ARCH_HAS_MMIO_FLUSH
 	select LIBNVDIMM
 	help
 	  Infrastructure to probe ACPI 6 compliant platforms for
diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
index 7c2638f914a9..56fff0141636 100644
--- a/drivers/acpi/nfit.c
+++ b/drivers/acpi/nfit.c
@@ -1017,7 +1017,7 @@ static u64 read_blk_stat(struct nfit_blk *nfit_blk, unsigned int bw)
 	if (mmio->num_lines)
 		offset = to_interleave_offset(offset, mmio);
 
-	return readq(mmio->base + offset);
+	return readq(mmio->addr.base + offset);
 }
 
 static void write_blk_ctl(struct nfit_blk *nfit_blk, unsigned int bw,
@@ -1042,11 +1042,11 @@ static void write_blk_ctl(struct nfit_blk *nfit_blk, unsigned int bw,
 	if (mmio->num_lines)
 		offset = to_interleave_offset(offset, mmio);
 
-	writeq(cmd, mmio->base + offset);
+	writeq(cmd, mmio->addr.base + offset);
 	wmb_blk(nfit_blk);
 
 	if (nfit_blk->dimm_flags & ND_BLK_DCR_LATCH)
-		readq(mmio->base + offset);
+		readq(mmio->addr.base + offset);
 }
 
 static int acpi_nfit_blk_single_io(struct nfit_blk *nfit_blk,
@@ -1078,11 +1078,16 @@ static int acpi_nfit_blk_single_io(struct nfit_blk *nfit_blk,
 		}
 
 		if (rw)
-			memcpy_to_pmem(mmio->aperture + offset,
+			memcpy_to_pmem(mmio->addr.aperture + offset,
 					iobuf + copied, c);
-		else
+		else {
+			if (nfit_blk->dimm_flags & ND_BLK_READ_FLUSH)
+				mmio_flush_range((void __force *)
+					mmio->addr.aperture + offset, c);
+
 			memcpy_from_pmem(iobuf + copied,
-					mmio->aperture + offset, c);
+					mmio->addr.aperture + offset, c);
+		}
 
 		copied += c;
 		len -= c;
@@ -1129,7 +1134,10 @@ static void nfit_spa_mapping_release(struct kref *kref)
 
 	WARN_ON(!mutex_is_locked(&acpi_desc->spa_map_mutex));
 	dev_dbg(acpi_desc->dev, "%s: SPA%d\n", __func__, spa->range_index);
-	iounmap(spa_map->iomem);
+	if (spa_map->type == SPA_MAP_APERTURE)
+		memunmap((void __force *)spa_map->addr.aperture);
+	else
+		iounmap(spa_map->addr.base);
 	release_mem_region(spa->address, spa->length);
 	list_del(&spa_map->list);
 	kfree(spa_map);
@@ -1175,7 +1183,7 @@ static void __iomem *__nfit_spa_map(struct acpi_nfit_desc *acpi_desc,
 	spa_map = find_spa_mapping(acpi_desc, spa);
 	if (spa_map) {
 		kref_get(&spa_map->kref);
-		return spa_map->iomem;
+		return spa_map->addr.base;
 	}
 
 	spa_map = kzalloc(sizeof(*spa_map), GFP_KERNEL);
@@ -1191,20 +1199,19 @@ static void __iomem *__nfit_spa_map(struct acpi_nfit_desc *acpi_desc,
 	if (!res)
 		goto err_mem;
 
-	if (type == SPA_MAP_APERTURE) {
-		/*
-		 * TODO: memremap_pmem() support, but that requires cache
-		 * flushing when the aperture is moved.
-		 */
-		spa_map->iomem = ioremap_wc(start, n);
-	} else
-		spa_map->iomem = ioremap_nocache(start, n);
+	spa_map->type = type;
+	if (type == SPA_MAP_APERTURE)
+		spa_map->addr.aperture = (void __pmem *)memremap(start, n,
+							ARCH_MEMREMAP_PMEM);
+	else
+		spa_map->addr.base = ioremap_nocache(start, n);
+
 
-	if (!spa_map->iomem)
+	if (!spa_map->addr.base)
 		goto err_map;
 
 	list_add_tail(&spa_map->list, &acpi_desc->spa_maps);
-	return spa_map->iomem;
+	return spa_map->addr.base;
 
  err_map:
 	release_mem_region(start, n);
@@ -1267,7 +1274,7 @@ static int acpi_nfit_blk_get_flags(struct nvdimm_bus_descriptor *nd_desc,
 		nfit_blk->dimm_flags = flags.flags;
 	else if (rc == -ENOTTY) {
 		/* fall back to a conservative default */
-		nfit_blk->dimm_flags = ND_BLK_DCR_LATCH;
+		nfit_blk->dimm_flags = ND_BLK_DCR_LATCH | ND_BLK_READ_FLUSH;
 		rc = 0;
 	} else
 		rc = -ENXIO;
@@ -1307,9 +1314,9 @@ static int acpi_nfit_blk_region_enable(struct nvdimm_bus *nvdimm_bus,
 	/* map block aperture memory */
 	nfit_blk->bdw_offset = nfit_mem->bdw->offset;
 	mmio = &nfit_blk->mmio[BDW];
-	mmio->base = nfit_spa_map(acpi_desc, nfit_mem->spa_bdw,
+	mmio->addr.base = nfit_spa_map(acpi_desc, nfit_mem->spa_bdw,
 			SPA_MAP_APERTURE);
-	if (!mmio->base) {
+	if (!mmio->addr.base) {
 		dev_dbg(dev, "%s: %s failed to map bdw\n", __func__,
 				nvdimm_name(nvdimm));
 		return -ENOMEM;
@@ -1330,9 +1337,9 @@ static int acpi_nfit_blk_region_enable(struct nvdimm_bus *nvdimm_bus,
 	nfit_blk->cmd_offset = nfit_mem->dcr->command_offset;
 	nfit_blk->stat_offset = nfit_mem->dcr->status_offset;
 	mmio = &nfit_blk->mmio[DCR];
-	mmio->base = nfit_spa_map(acpi_desc, nfit_mem->spa_dcr,
+	mmio->addr.base = nfit_spa_map(acpi_desc, nfit_mem->spa_dcr,
 			SPA_MAP_CONTROL);
-	if (!mmio->base) {
+	if (!mmio->addr.base) {
 		dev_dbg(dev, "%s: %s failed to map dcr\n", __func__,
 				nvdimm_name(nvdimm));
 		return -ENOMEM;
@@ -1399,7 +1406,7 @@ static void acpi_nfit_blk_region_disable(struct nvdimm_bus *nvdimm_bus,
 	for (i = 0; i < 2; i++) {
 		struct nfit_blk_mmio *mmio = &nfit_blk->mmio[i];
 
-		if (mmio->base)
+		if (mmio->addr.base)
 			nfit_spa_unmap(acpi_desc, mmio->spa);
 	}
 	nd_blk_region_set_provider_data(ndbr, NULL);
diff --git a/drivers/acpi/nfit.h b/drivers/acpi/nfit.h
index f2c2bb751882..7e740156b9c2 100644
--- a/drivers/acpi/nfit.h
+++ b/drivers/acpi/nfit.h
@@ -41,6 +41,7 @@ enum nfit_uuids {
 };
 
 enum {
+	ND_BLK_READ_FLUSH = 1,
 	ND_BLK_DCR_LATCH = 2,
 };
 
@@ -117,12 +118,16 @@ enum nd_blk_mmio_selector {
 	DCR,
 };
 
+struct nd_blk_addr {
+	union {
+		void __iomem *base;
+		void __pmem  *aperture;
+	};
+};
+
 struct nfit_blk {
 	struct nfit_blk_mmio {
-		union {
-			void __iomem *base;
-			void __pmem  *aperture;
-		};
+		struct nd_blk_addr addr;
 		u64 size;
 		u64 base_offset;
 		u32 line_size;
@@ -149,7 +154,8 @@ struct nfit_spa_mapping {
 	struct acpi_nfit_system_address *spa;
 	struct list_head list;
 	struct kref kref;
-	void __iomem *iomem;
+	enum spa_map_type type;
+	struct nd_blk_addr addr;
 };
 
 static inline struct nfit_spa_mapping *to_spa_map(struct kref *kref)