powerpc/powernv: Add OPAL exports attributes to sysfs

New versions of OPAL have a device node /ibm,opal/firmware/exports, each
property of which describes a range of memory in OPAL that Linux might
want to export to userspace for debugging.

This patch adds a sysfs file under 'opal/exports' for each property
found there, and makes it read-only by root.
Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>
[mpe: Drop counting of props, rename to attr, free on sysfs error, c'log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal.c

@@ -595,6 +595,79 @@ static void opal_export_symmap(void)
 		pr_warn("Error %d creating OPAL symbols file\n", rc);
 }
 
+static ssize_t export_attr_read(struct file *fp, struct kobject *kobj,
+				struct bin_attribute *bin_attr, char *buf,
+				loff_t off, size_t count)
+{
+	return memory_read_from_buffer(buf, count, &off, bin_attr->private,
+				       bin_attr->size);
+}
+
+/*
+ * opal_export_attrs: creates a sysfs node for each property listed in
+ * the device-tree under /ibm,opal/firmware/exports/
+ * All new sysfs nodes are created under /opal/exports/.
+ * This allows for reserved memory regions (e.g. HDAT) to be read.
+ * The new sysfs nodes are only readable by root.
+ */
+static void opal_export_attrs(void)
+{
+	struct bin_attribute *attr;
+	struct device_node *np;
+	struct property *prop;
+	struct kobject *kobj;
+	u64 vals[2];
+	int rc;
+
+	np = of_find_node_by_path("/ibm,opal/firmware/exports");
+	if (!np)
+		return;
+
+	/* Create new 'exports' directory - /sys/firmware/opal/exports */
+	kobj = kobject_create_and_add("exports", opal_kobj);
+	if (!kobj) {
+		pr_warn("kobject_create_and_add() of exports failed\n");
+		return;
+	}
+
+	for_each_property_of_node(np, prop) {
+		if (!strcmp(prop->name, "name") || !strcmp(prop->name, "phandle"))
+			continue;
+
+		if (of_property_read_u64_array(np, prop->name, &vals[0], 2))
+			continue;
+
+		attr = kmalloc(sizeof(*attr), GFP_KERNEL);
+
+		if (attr == NULL) {
+			pr_warn("Failed kmalloc for bin_attribute!");
+			continue;
+		}
+
+		attr->attr.name = kstrdup(prop->name, GFP_KERNEL);
+		attr->attr.mode = 0400;
+		attr->read = export_attr_read;
+		attr->private = __va(vals[0]);
+		attr->size = vals[1];
+
+		if (attr->attr.name == NULL) {
+			pr_warn("Failed kstrdup for bin_attribute attr.name");
+			kfree(attr);
+			continue;
+		}
+
+		rc = sysfs_create_bin_file(kobj, attr);
+		if (rc) {
+			pr_warn("Error %d creating OPAL sysfs exports/%s file\n",
+				 rc, prop->name);
+			kfree(attr->attr.name);
+			kfree(attr);
+		}
+	}
+
+	of_node_put(np);
+}
+
 static void __init opal_dump_region_init(void)
 {
 	void *addr;
@@ -733,6 +806,9 @@ static int __init opal_init(void)
 		opal_msglog_sysfs_init();
 	}
 
+	/* Export all properties */
+	opal_export_attrs();
+
 	/* Initialize platform devices: IPMI backend, PRD & flash interface */
 	opal_pdev_init("ibm,opal-ipmi");
 	opal_pdev_init("ibm,opal-flash");