HID: i2c-hid: add DT bindings

Add device tree based support for HID over I2C devices.

Tested on an Odroid-X board with a Synaptics touchpad.

Signed-off-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

Documentation/devicetree/bindings/hid/hid-over-i2c.txt

···
+* HID over I2C Device-Tree bindings
+
+HID over I2C provides support for various Human Interface Devices over the
+I2C bus. These devices can be for example touchpads, keyboards, touch screens
+or sensors.
+
+The specification has been written by Microsoft and is currently available here:
+http://msdn.microsoft.com/en-us/library/windows/hardware/hh852380.aspx
+
+If this binding is used, the kernel module i2c-hid will handle the communication
+with the device and the generic hid core layer will handle the protocol.
+
+Required properties:
+- compatible: must be "hid-over-i2c"
+- reg: i2c slave address
+- hid-descr-addr: HID descriptor address
+- interrupt-parent: the phandle for the interrupt controller
+- interrupts: interrupt line
+
+Example:
+
+	i2c-hid-dev@2c {
+		compatible = "hid-over-i2c";
+		reg = <0x2c>;
+		hid-descr-addr = <0x0020>;
+		interrupt-parent = <&gpx3>;
+		interrupts = <3 2>;
+	};

drivers/hid/i2c-hid/i2c-hid.c

···
 #include <linux/hid.h>
 #include <linux/mutex.h>
 #include <linux/acpi.h>
+#include <linux/of.h>
 
 #include <linux/i2c/i2c-hid.h>
 
···
 }
 #endif
 
+#ifdef CONFIG_OF
+static int i2c_hid_of_probe(struct i2c_client *client,
+		struct i2c_hid_platform_data *pdata)
+{
+	struct device *dev = &client->dev;
+	u32 val;
+	int ret;
+
+	ret = of_property_read_u32(dev->of_node, "hid-descr-addr", &val);
+	if (ret) {
+		dev_err(&client->dev, "HID register address not provided\n");
+		return -ENODEV;
+	}
+	if (val >> 16) {
+		dev_err(&client->dev, "Bad HID register address: 0x%08x\n",
+			val);
+		return -EINVAL;
+	}
+	pdata->hid_descriptor_address = val;
+
+	return 0;
+}
+
+static const struct of_device_id i2c_hid_of_match[] = {
+	{ .compatible = "hid-over-i2c" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, i2c_hid_of_match);
+#else
+static inline int i2c_hid_of_probe(struct i2c_client *client,
+		struct i2c_hid_platform_data *pdata)
+{
+	return -ENODEV;
+}
+#endif
+
 static int i2c_hid_probe(struct i2c_client *client,
 			 const struct i2c_device_id *dev_id)
 {
···
 	if (!ihid)
 		return -ENOMEM;
 
-	if (!platform_data) {
+	if (client->dev.of_node) {
+		ret = i2c_hid_of_probe(client, &ihid->pdata);
+		if (ret)
+			goto err;
+	} else if (!platform_data) {
 		ret = i2c_hid_acpi_pdata(client, &ihid->pdata);
 		if (ret) {
 			dev_err(&client->dev,
···
 		.owner	= THIS_MODULE,
 		.pm	= &i2c_hid_pm,
 		.acpi_match_table = ACPI_PTR(i2c_hid_acpi_match),
+		.of_match_table = of_match_ptr(i2c_hid_of_match),
 	},
 
 	.probe		= i2c_hid_probe,

include/linux/i2c/i2c-hid.h

···
  * @hid_descriptor_address: i2c register where the HID descriptor is stored.
  *
  * Note that it is the responsibility of the platform driver (or the acpi 5.0
- * driver) to setup the irq related to the gpio in the struct i2c_board_info.
+ * driver, or the flattened device tree) to setup the irq related to the gpio in
+ * the struct i2c_board_info.
  * The platform driver should also setup the gpio according to the device:
  *
  * A typical example is the following: