libnvdimm: expose platform persistence attribute for nd_region

Providing a sysfs attribute for nd_region that shows the persistence
capabilities for the platform.
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/nvdimm/region_devs.c

@@ -528,6 +528,18 @@ static ssize_t resource_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(resource);
 
+static ssize_t persistence_domain_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct nd_region *nd_region = to_nd_region(dev);
+	unsigned long flags = nd_region->flags;
+
+	return sprintf(buf, "%s%s\n",
+			flags & BIT(ND_REGION_PERSIST_CACHE) ? "cpu_cache " : "",
+			flags & BIT(ND_REGION_PERSIST_MEMCTRL) ? "memory_controller " : "");
+}
+static DEVICE_ATTR_RO(persistence_domain);
+
 static struct attribute *nd_region_attributes[] = {
 	&dev_attr_size.attr,
 	&dev_attr_nstype.attr,
@@ -543,6 +555,7 @@ static struct attribute *nd_region_attributes[] = {
 	&dev_attr_init_namespaces.attr,
 	&dev_attr_badblocks.attr,
 	&dev_attr_resource.attr,
+	&dev_attr_persistence_domain.attr,
 	NULL,
 };