i2c: Use rwsem instead of mutex for board info

By using rwsem we can easily manage recursive calls of
i2c_scan_static_board_info() function without breaking the locking.
Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/i2c-boardinfo.c

@@ -18,6 +18,7 @@
 
 #include <linux/kernel.h>
 #include <linux/i2c.h>
+#include <linux/rwsem.h>
 
 #include "i2c-core.h"
 
@@ -25,7 +26,7 @@
 /* These symbols are exported ONLY FOR the i2c core.
  * No other users will be supported.
  */
-DEFINE_MUTEX(__i2c_board_lock);
+DECLARE_RWSEM(__i2c_board_lock);
 EXPORT_SYMBOL_GPL(__i2c_board_lock);
 
 LIST_HEAD(__i2c_board_list);
@@ -63,7 +64,7 @@ i2c_register_board_info(int busnum,
 {
 	int status;
 
-	mutex_lock(&__i2c_board_lock);
+	down_write(&__i2c_board_lock);
 
 	/* dynamic bus numbers will be assigned after the last static one */
 	if (busnum >= __i2c_first_dynamic_bus_num)
@@ -84,7 +85,7 @@ i2c_register_board_info(int busnum,
 		list_add_tail(&devinfo->list, &__i2c_board_list);
 	}
 
-	mutex_unlock(&__i2c_board_lock);
+	up_write(&__i2c_board_lock);
 
 	return status;
 }

drivers/i2c/i2c-core.c

@@ -33,6 +33,7 @@
 #include <linux/completion.h>
 #include <linux/hardirq.h>
 #include <linux/irqflags.h>
+#include <linux/rwsem.h>
 #include <asm/uaccess.h>
 
 #include "i2c-core.h"
@@ -509,7 +510,7 @@ static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
 {
 	struct i2c_devinfo	*devinfo;
 
-	mutex_lock(&__i2c_board_lock);
+	down_read(&__i2c_board_lock);
 	list_for_each_entry(devinfo, &__i2c_board_list, list) {
 		if (devinfo->busnum == adapter->nr
 				&& !i2c_new_device(adapter,
@@ -518,7 +519,7 @@ static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
 				"Can't create device at 0x%02x\n",
 				devinfo->board_info.addr);
 	}
-	mutex_unlock(&__i2c_board_lock);
+	up_read(&__i2c_board_lock);
 }
 
 static int i2c_do_add_adapter(struct device_driver *d, void *data)

drivers/i2c/i2c-core.h

@@ -16,6 +16,8 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <linux/rwsem.h>
+
 struct i2c_devinfo {
 	struct list_head	list;
 	int			busnum;
@@ -25,7 +27,7 @@ struct i2c_devinfo {
 /* board_lock protects board_list and first_dynamic_bus_num.
  * only i2c core components are allowed to use these symbols.
  */
-extern struct mutex	__i2c_board_lock;
+extern struct rw_semaphore	__i2c_board_lock;
 extern struct list_head	__i2c_board_list;
 extern int		__i2c_first_dynamic_bus_num;