driver core: Add class_attr_string for simple read-only string

Several drivers just export a static string as class attributes.

Use the new extensible attribute support to define a simple
CLASS_ATTR_STRING() macro for this.

This will allow to remove code from drivers in followon patches.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/class.c

@@ -490,6 +490,16 @@ void class_interface_unregister(struct class_interface *class_intf)
 	class_put(parent);
 }
 
+ssize_t show_class_attr_string(struct class *class, struct class_attribute *attr,
+                        	char *buf)
+{
+	struct class_attribute_string *cs;
+	cs = container_of(attr, struct class_attribute_string, attr);
+	return snprintf(buf, PAGE_SIZE, "%s\n", cs->str);
+}
+
+EXPORT_SYMBOL_GPL(show_class_attr_string);
+
 struct class_compat {
 	struct kobject *kobj;
 };

include/linux/device.h

@@ -265,6 +265,23 @@ extern int __must_check class_create_file(struct class *class,
 extern void class_remove_file(struct class *class,
 			      const struct class_attribute *attr);
 
+/* Simple class attribute that is just a static string */
+
+struct class_attribute_string {
+	struct class_attribute attr;
+	char *str;
+};
+
+/* Currently read-only only */
+#define _CLASS_ATTR_STRING(_name, _mode, _str) \
+	{ __ATTR(_name, _mode, show_class_attr_string, NULL), _str }
+#define CLASS_ATTR_STRING(_name, _mode, _str) \
+	struct class_attribute_string class_attr_##_name = \
+		_CLASS_ATTR_STRING(_name, _mode, _str)
+
+extern ssize_t show_class_attr_string(struct class *class, struct class_attribute *attr,
+                        char *buf);
+
 struct class_interface {
 	struct list_head	node;
 	struct class		*class;