i2c: core: fix lockdep warning for sparsely nested adapter chain

When adapters are chained in a sparse manner (with intermediate MFD devices,
for instance) the code currently fails to use the correct subclass for
the adapter's bus_lock which leads to false-positive lockdep warnings.

Fix this by walking the entire pedigree of the device and count all
adapters along the way instead of just checking the immediate parent.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Author: zonque

drivers/i2c/i2c-core-base.c

@@ -1194,9 +1194,11 @@ static void i2c_adapter_dev_release(struct device *dev)
 unsigned int i2c_adapter_depth(struct i2c_adapter *adapter)
 {
 	unsigned int depth = 0;
+	struct device *parent;
 
-	while ((adapter = i2c_parent_is_i2c_adapter(adapter)))
-		depth++;
+	for (parent = adapter->dev.parent; parent; parent = parent->parent)
+		if (parent->type == &i2c_adapter_type)
+			depth++;
 
 	WARN_ONCE(depth >= MAX_LOCKDEP_SUBCLASSES,
 		  "adapter depth exceeds lockdep subclass limit\n");