i2c: 'i2c-bus' node support for v4.8-rc1

This includes the device tree binding and I2C core changes to support
 the i2c-bus subnode that I2C masters can use to describe their slaves
 in a separate namespace and therefore avoid clashing with potentially
 other subnodes.
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Merge tag 'tegra-for-4.8-i2c' of git://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux into i2c/for-next

[wsa: fell through the cracks, applied to 4.9 now]

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

i2c: 'i2c-bus' node support for v4.8-rc1

This includes the device tree binding and I2C core changes to support
the i2c-bus subnode that I2C masters can use to describe their slaves
in a separate namespace and therefore avoid clashing with potentially
other subnodes.

Documentation/devicetree/bindings/i2c/i2c.txt

@@ -32,6 +32,14 @@ wants to support one of the below features, it should adapt the bindings below.
 - clock-frequency
 	frequency of bus clock in Hz.
 
+- i2c-bus
+	For I2C adapters that have child nodes that are a mixture of both I2C
+	devices and non-I2C devices, the 'i2c-bus' subnode can be used for
+	populating I2C devices. If the 'i2c-bus' subnode is present, only
+	subnodes of this will be considered as I2C slaves. The properties,
+	'#address-cells' and '#size-cells' must be defined under this subnode
+	if present.
+
 - i2c-scl-falling-time-ns
 	Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
 	specification.

drivers/i2c/i2c-core.c

@@ -1680,7 +1680,7 @@ static struct i2c_client *of_i2c_register_device(struct i2c_adapter *adap,
 
 static void of_i2c_register_devices(struct i2c_adapter *adap)
 {
-	struct device_node *node;
+	struct device_node *bus, *node;
 
 	/* Only register child devices if the adapter has a node pointer set */
 	if (!adap->dev.of_node)
@@ -1688,11 +1688,17 @@ static void of_i2c_register_devices(struct i2c_adapter *adap)
 
 	dev_dbg(&adap->dev, "of_i2c: walking child nodes\n");
 
-	for_each_available_child_of_node(adap->dev.of_node, node) {
+	bus = of_get_child_by_name(adap->dev.of_node, "i2c-bus");
+	if (!bus)
+		bus = of_node_get(adap->dev.of_node);
+
+	for_each_available_child_of_node(bus, node) {
 		if (of_node_test_and_set_flag(node, OF_POPULATED))
 			continue;
 		of_i2c_register_device(adap, node);
 	}
+
+	of_node_put(bus);
 }
 
 static int of_dev_node_match(struct device *dev, void *data)