i2c: add a warning to i2c_adapter_depth()

This routine is only used together with lockdep for nested locking.
The number of lock subclasses is limited to 8 as defined in lockdep.h

Emit a warning if the adapter depth exceeds the maximum number of
lockdep subclasses.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Peter Rosin <peda@axentia.se>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core.c

@@ -1433,6 +1433,9 @@ unsigned int i2c_adapter_depth(struct i2c_adapter *adapter)
 	while ((adapter = i2c_parent_is_i2c_adapter(adapter)))
 		depth++;
 
+	WARN_ONCE(depth >= MAX_LOCKDEP_SUBCLASSES,
+		  "adapter depth exceeds lockdep subclass limit\n");
+
 	return depth;
 }
 EXPORT_SYMBOL_GPL(i2c_adapter_depth);