clk: of-provider: look at parent if registered device has no provider info

It seems to be usual for MFD devices that the created 'clock sub-device'
do not have own DT node. The clock provider information is usually in the
main device node which is owned by the MFD device. Change the devm variant
of clk of-provider registration to check the parent device node if given
device has no own node or if the node does not contain the #clock-cells
property. In such case use the parent node if it contains the #clock-cells.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
[sboyd@kernel.org: Add some comment in the code and pull out logic into
a single function to return the provider device_node pointer]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk.c

@@ -3893,14 +3893,36 @@ static void devm_of_clk_release_provider(struct device *dev, void *res)
 	of_clk_del_provider(*(struct device_node **)res);
 }
 
+/*
+ * We allow a child device to use its parent device as the clock provider node
+ * for cases like MFD sub-devices where the child device driver wants to use
+ * devm_*() APIs but not list the device in DT as a sub-node.
+ */
+static struct device_node *get_clk_provider_node(struct device *dev)
+{
+	struct device_node *np, *parent_np;
+
+	np = dev->of_node;
+	parent_np = dev->parent ? dev->parent->of_node : NULL;
+
+	if (!of_find_property(np, "#clock-cells", NULL))
+		if (of_find_property(parent_np, "#clock-cells", NULL))
+			np = parent_np;
+
+	return np;
+}
+
 /**
  * devm_of_clk_add_hw_provider() - Managed clk provider node registration
  * @dev: Device acting as the clock provider (used for DT node and lifetime)
  * @get: callback for decoding clk_hw
  * @data: context pointer for @get callback
  *
- * Registers clock provider for given device's node. Provider is automatically
- * released at device exit.
+ * Registers clock provider for given device's node. If the device has no DT
+ * node or if the device node lacks of clock provider information (#clock-cells)
+ * then the parent device's node is scanned for this information. If parent node
+ * has the #clock-cells then it is used in registration. Provider is
+ * automatically released at device exit.
  *
  * Return: 0 on success or an errno on failure.
  */
@@ -3917,7 +3939,7 @@ int devm_of_clk_add_hw_provider(struct device *dev,
 	if (!ptr)
 		return -ENOMEM;
 
-	np = dev->of_node;
+	np = get_clk_provider_node(dev);
 	ret = of_clk_add_hw_provider(np, get, data);
 	if (!ret) {
 		*ptr = np;
@@ -3968,9 +3990,10 @@ static int devm_clk_provider_match(struct device *dev, void *res, void *data)
 void devm_of_clk_del_provider(struct device *dev)
 {
 	int ret;
+	struct device_node *np = get_clk_provider_node(dev);
 
 	ret = devres_release(dev, devm_of_clk_release_provider,
-			     devm_clk_provider_match, dev->of_node);
+			     devm_clk_provider_match, np);
 
 	WARN_ON(ret);
 }