clk: Use parent node pointer during registration if necessary

Sometimes clk drivers are attached to devices which are children of a
parent device that is connected to a node in DT. This happens when
devices are MFD-ish and the parent device driver mostly registers child
devices to match against drivers placed in their respective subsystem
directories like drivers/clk, drivers/regulator, etc. When the clk
driver calls clk_register() with a device pointer, that struct device
pointer won't have a device_node associated with it because it was
created purely in software as a way to partition logic to a subsystem.

This causes problems for the way we find parent clks for the clks
registered by these child devices because we look at the registering
device's device_node pointer to lookup 'clocks' and 'clock-names'
properties. Let's use the parent device's device_node pointer if the
registering device doesn't have a device_node but the parent does. This
simplifies clk registration code by avoiding the need to assign some
device_node to the device registering the clk.

Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Reported-by: Niklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lkml.kernel.org/r/20191230190455.141339-1-sboyd@kernel.org
[sboyd@kernel.org: Fixup kernel-doc notation]
Reviewed-by: Niklas Cassel <nks@flawful.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/clk/clk.c

@@ -3719,6 +3719,28 @@ fail_out:
 	return ERR_PTR(ret);
 }
 
+/**
+ * dev_or_parent_of_node() - Get device node of @dev or @dev's parent
+ * @dev: Device to get device node of
+ *
+ * Return: device node pointer of @dev, or the device node pointer of
+ * @dev->parent if dev doesn't have a device node, or NULL if neither
+ * @dev or @dev->parent have a device node.
+ */
+static struct device_node *dev_or_parent_of_node(struct device *dev)
+{
+	struct device_node *np;
+
+	if (!dev)
+		return NULL;
+
+	np = dev_of_node(dev);
+	if (!np)
+		np = dev_of_node(dev->parent);
+
+	return np;
+}
+
 /**
  * clk_register - allocate a new clock, register it and return an opaque cookie
  * @dev: device that is registering this clock
@@ -3734,7 +3756,7 @@ fail_out:
  */
 struct clk *clk_register(struct device *dev, struct clk_hw *hw)
 {
-	return __clk_register(dev, dev_of_node(dev), hw);
+	return __clk_register(dev, dev_or_parent_of_node(dev), hw);
 }
 EXPORT_SYMBOL_GPL(clk_register);
 
@@ -3750,7 +3772,8 @@ EXPORT_SYMBOL_GPL(clk_register);
  */
 int clk_hw_register(struct device *dev, struct clk_hw *hw)
 {
-	return PTR_ERR_OR_ZERO(__clk_register(dev, dev_of_node(dev), hw));
+	return PTR_ERR_OR_ZERO(__clk_register(dev, dev_or_parent_of_node(dev),
+			       hw));
 }
 EXPORT_SYMBOL_GPL(clk_hw_register);