acpi: nfit: Add support for detect platform CPU cache flush on power loss

In ACPI 6.2a the platform capability structure has been added to the NFIT
tables. That provides software the ability to determine whether a system
supports the auto flushing of CPU caches on power loss. If the capability
is supported, we do not need to do dax_flush(). Plumbing the path to set the
property on per region from the NFIT tables.

This patch depends on the ACPI NFIT 6.2a platform capabilities support code
in include/acpi/actbl1.h.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

drivers/acpi/nfit/core.c

@@ -838,6 +838,18 @@ static bool add_flush(struct acpi_nfit_desc *acpi_desc,
 	return true;
 }
 
+static bool add_platform_cap(struct acpi_nfit_desc *acpi_desc,
+		struct acpi_nfit_capabilities *pcap)
+{
+	struct device *dev = acpi_desc->dev;
+	u32 mask;
+
+	mask = (1 << (pcap->highest_capability + 1)) - 1;
+	acpi_desc->platform_cap = pcap->capabilities & mask;
+	dev_dbg(dev, "%s: cap: %#x\n", __func__, acpi_desc->platform_cap);
+	return true;
+}
+
 static void *add_table(struct acpi_nfit_desc *acpi_desc,
 		struct nfit_table_prev *prev, void *table, const void *end)
 {
@@ -883,6 +895,10 @@ static void *add_table(struct acpi_nfit_desc *acpi_desc,
 	case ACPI_NFIT_TYPE_SMBIOS:
 		dev_dbg(dev, "%s: smbios\n", __func__);
 		break;
+	case ACPI_NFIT_TYPE_CAPABILITIES:
+		if (!add_platform_cap(acpi_desc, table))
+			return err;
+		break;
 	default:
 		dev_err(dev, "unknown table '%d' parsing nfit\n", hdr->type);
 		break;
@@ -2656,6 +2672,9 @@ static int acpi_nfit_register_region(struct acpi_nfit_desc *acpi_desc,
 	else
 		ndr_desc->numa_node = NUMA_NO_NODE;
 
+	if(acpi_desc->platform_cap & ACPI_NFIT_CAPABILITY_CACHE_FLUSH)
+		set_bit(ND_REGION_PERSIST_CACHE, &ndr_desc->flags);
+
 	list_for_each_entry(nfit_memdev, &acpi_desc->memdevs, list) {
 		struct acpi_nfit_memory_map *memdev = nfit_memdev->memdev;
 		struct nd_mapping_desc *mapping;
@@ -3464,6 +3483,7 @@ static __init int nfit_init(void)
 	BUILD_BUG_ON(sizeof(struct acpi_nfit_smbios) != 9);
 	BUILD_BUG_ON(sizeof(struct acpi_nfit_control_region) != 80);
 	BUILD_BUG_ON(sizeof(struct acpi_nfit_data_region) != 40);
+	BUILD_BUG_ON(sizeof(struct acpi_nfit_capabilities) != 16);
 
 	guid_parse(UUID_VOLATILE_MEMORY, &nfit_uuid[NFIT_SPA_VOLATILE]);
 	guid_parse(UUID_PERSISTENT_MEMORY, &nfit_uuid[NFIT_SPA_PM]);

drivers/acpi/nfit/nfit.h

@@ -202,6 +202,7 @@ struct acpi_nfit_desc {
 	unsigned long dimm_cmd_force_en;
 	unsigned long bus_cmd_force_en;
 	unsigned long bus_nfit_cmd_force_en;
+	unsigned int platform_cap;
 	int (*blk_do_io)(struct nd_blk_region *ndbr, resource_size_t dpa,
 			void *iobuf, u64 len, int rw);
 };

drivers/nvdimm/pmem.c

@@ -35,6 +35,7 @@
 #include "pmem.h"
 #include "pfn.h"
 #include "nd.h"
+#include "nd-core.h"
 
 static struct device *to_dev(struct pmem_device *pmem)
 {
@@ -334,7 +335,8 @@ static int pmem_attach_disk(struct device *dev,
 		dev_warn(dev, "unable to guarantee persistence of writes\n");
 		fua = 0;
 	}
-	wbc = nvdimm_has_cache(nd_region);
+	wbc = nvdimm_has_cache(nd_region) &&
+		!test_bit(ND_REGION_PERSIST_CACHE, &nd_region->flags);
 
 	if (!devm_request_mem_region(dev, res->start, resource_size(res),
 				dev_name(&ndns->dev))) {

include/linux/libnvdimm.h

@@ -47,6 +47,11 @@ enum {
 
 	/* region flag indicating to direct-map persistent memory by default */
 	ND_REGION_PAGEMAP = 0,
+	/*
+	 * Platform ensures entire CPU store data path is flushed to pmem on
+	 * system power loss.
+	 */
+	ND_REGION_PERSIST_CACHE = 1,
 
 	/* mark newly adjusted resources as requiring a label update */
 	DPA_RESOURCE_ADJUSTED = 1 << 0,