Input: add new sun4i-lradc-keys driver

Allwinnner sunxi SoCs have a low resolution adc (called lradc) which is
specifically designed to have various (tablet) keys (ie home, back, search,
etc). attached to it using a resistor network. This adds a driver for this.

There are 2 channels, currently this driver only supports chan0 since there
are no boards known to use chan1.

This has been tested on an olimex a10s-olinuxino-micro, a13-olinuxino, and
a20-olinuxino-micro.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/input/sun4i-lradc-keys.txt b/Documentation/devicetree/bindings/input/sun4i-lradc-keys.txt
new file mode 100644
index 000000000000..b9c32f6fd687
--- /dev/null
+++ b/Documentation/devicetree/bindings/input/sun4i-lradc-keys.txt
@@ -0,0 +1,62 @@
+Allwinner sun4i low res adc attached tablet keys
+------------------------------------------------
+
+Required properties:
+ - compatible: "allwinner,sun4i-a10-lradc-keys"
+ - reg: mmio address range of the chip
+ - interrupts: interrupt to which the chip is connected
+ - vref-supply: powersupply for the lradc reference voltage
+
+Each key is represented as a sub-node of "allwinner,sun4i-a10-lradc-keys":
+
+Required subnode-properties:
+	- label: Descriptive name of the key.
+	- linux,code: Keycode to emit.
+	- channel: Channel this key is attached to, mut be 0 or 1.
+	- voltage: Voltage in µV at lradc input when this key is pressed.
+
+Example:
+
+#include <dt-bindings/input/input.h>
+
+	lradc: lradc@01c22800 {
+		compatible = "allwinner,sun4i-a10-lradc-keys";
+		reg = <0x01c22800 0x100>;
+		interrupts = <31>;
+		vref-supply = <&reg_vcc3v0>;
+
+		button@191 {
+			label = "Volume Up";
+			linux,code = <KEY_VOLUMEUP>;
+			channel = <0>;
+			voltage = <191274>;
+		};
+
+		button@392 {
+			label = "Volume Down";
+			linux,code = <KEY_VOLUMEDOWN>;
+			channel = <0>;
+			voltage = <392644>;
+		};
+
+		button@601 {
+			label = "Menu";
+			linux,code = <KEY_MENU>;
+			channel = <0>;
+			voltage = <601151>;
+		};
+
+		button@795 {
+			label = "Enter";
+			linux,code = <KEY_ENTER>;
+			channel = <0>;
+			voltage = <795090>;
+		};
+
+		button@987 {
+			label = "Home";
+			linux,code = <KEY_HOMEPAGE>;
+			channel = <0>;
+			voltage = <987387>;
+		};
+	};