dax: add region 'id', 'size', and 'align' attributes

While this information is available by looking at the nvdimm parent
device that may not always be the case when/if we add support for other
memory regions. Tooling should not depend on walking a given ancestor
topology that is not guaranteed by the device's class. For example, a
device-dax instance will always have a dax_region parent, but it may not
always have a libnvdimm "dax" device as a grandparent.
Reported-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dax/dax.c

@@ -75,6 +75,73 @@ struct dax_dev {
 	struct resource res[0];
 };
 
+static ssize_t id_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dax_region *dax_region;
+	ssize_t rc = -ENXIO;
+
+	device_lock(dev);
+	dax_region = dev_get_drvdata(dev);
+	if (dax_region)
+		rc = sprintf(buf, "%d\n", dax_region->id);
+	device_unlock(dev);
+
+	return rc;
+}
+static DEVICE_ATTR_RO(id);
+
+static ssize_t region_size_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dax_region *dax_region;
+	ssize_t rc = -ENXIO;
+
+	device_lock(dev);
+	dax_region = dev_get_drvdata(dev);
+	if (dax_region)
+		rc = sprintf(buf, "%llu\n", (unsigned long long)
+				resource_size(&dax_region->res));
+	device_unlock(dev);
+
+	return rc;
+}
+static struct device_attribute dev_attr_region_size = __ATTR(size, 0444,
+		region_size_show, NULL);
+
+static ssize_t align_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dax_region *dax_region;
+	ssize_t rc = -ENXIO;
+
+	device_lock(dev);
+	dax_region = dev_get_drvdata(dev);
+	if (dax_region)
+		rc = sprintf(buf, "%u\n", dax_region->align);
+	device_unlock(dev);
+
+	return rc;
+}
+static DEVICE_ATTR_RO(align);
+
+static struct attribute *dax_region_attributes[] = {
+	&dev_attr_region_size.attr,
+	&dev_attr_align.attr,
+	&dev_attr_id.attr,
+	NULL,
+};
+
+static const struct attribute_group dax_region_attribute_group = {
+	.name = "dax_region",
+	.attrs = dax_region_attributes,
+};
+
+static const struct attribute_group *dax_region_attribute_groups[] = {
+	&dax_region_attribute_group,
+	NULL,
+};
+
 static struct inode *dax_alloc_inode(struct super_block *sb)
 {
 	return kmem_cache_alloc(dax_cache, GFP_KERNEL);
@@ -200,12 +267,31 @@ void dax_region_put(struct dax_region *dax_region)
 }
 EXPORT_SYMBOL_GPL(dax_region_put);
 
+static void dax_region_unregister(void *region)
+{
+	struct dax_region *dax_region = region;
+
+	sysfs_remove_groups(&dax_region->dev->kobj,
+			dax_region_attribute_groups);
+	dax_region_put(dax_region);
+}
+
 struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		struct resource *res, unsigned int align, void *addr,
 		unsigned long pfn_flags)
 {
 	struct dax_region *dax_region;
 
+	/*
+	 * The DAX core assumes that it can store its private data in
+	 * parent->driver_data. This WARN is a reminder / safeguard for
+	 * developers of device-dax drivers.
+	 */
+	if (dev_get_drvdata(parent)) {
+		dev_WARN(parent, "dax core failed to setup private data\n");
+		return NULL;
+	}
+
 	if (!IS_ALIGNED(res->start, align)
 			|| !IS_ALIGNED(resource_size(res), align))
 		return NULL;
@@ -214,6 +300,7 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 	if (!dax_region)
 		return NULL;
 
+	dev_set_drvdata(parent, dax_region);
 	memcpy(&dax_region->res, res, sizeof(*res));
 	dax_region->pfn_flags = pfn_flags;
 	kref_init(&dax_region->kref);
@@ -222,7 +309,14 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 	dax_region->align = align;
 	dax_region->dev = parent;
 	dax_region->base = addr;
+	if (sysfs_create_groups(&parent->kobj, dax_region_attribute_groups)) {
+		kfree(dax_region);
+		return NULL;;
+	}
 
+	kref_get(&dax_region->kref);
+	if (devm_add_action_or_reset(parent, dax_region_unregister, dax_region))
+		return NULL;
 	return dax_region;
 }
 EXPORT_SYMBOL_GPL(alloc_dax_region);