Input: add generic GPIO-tilt driver

There exist tilt switches that simply report their tilt-state via
some gpios. The number and orientation of their axes can vary
depending on the switch used and the build of the device. Also two
or more one-axis switches could be combined to provide multi-dimensional
orientation.

One example of a device using such a switch is the family of Qisda
ebook readers, where the switch provides information about the
landscape / portrait orientation of the device. The example in
Documentation/input/gpio-tilt.txt documents exactly this one-axis
device.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

Documentation/input/gpio-tilt.txt

@@ -0,0 +1,103 @@
+Driver for tilt-switches connected via GPIOs
+============================================
+
+Generic driver to read data from tilt switches connected via gpios.
+Orientation can be provided by one or more than one tilt switches,
+i.e. each tilt switch providing one axis, and the number of axes
+is also not limited.
+
+
+Data structures:
+----------------
+
+The array of struct gpio in the gpios field is used to list the gpios
+that represent the current tilt state.
+
+The array of struct gpio_tilt_axis describes the axes that are reported
+to the input system. The values set therein are used for the
+input_set_abs_params calls needed to init the axes.
+
+The array of struct gpio_tilt_state maps gpio states to the corresponding
+values to report. The gpio state is represented as a bitfield where the
+bit-index corresponds to the index of the gpio in the struct gpio array.
+In the same manner the values stored in the axes array correspond to
+the elements of the gpio_tilt_axis-array.
+
+
+Example:
+--------
+
+Example configuration for a single TS1003 tilt switch that rotates around
+one axis in 4 steps and emitts the current tilt via two GPIOs.
+
+static int sg060_tilt_enable(struct device *dev) {
+	/* code to enable the sensors */
+};
+
+static void sg060_tilt_disable(struct device *dev) {
+	/* code to disable the sensors */
+};
+
+static struct gpio sg060_tilt_gpios[] = {
+	{ SG060_TILT_GPIO_SENSOR1, GPIOF_IN, "tilt_sensor1" },
+	{ SG060_TILT_GPIO_SENSOR2, GPIOF_IN, "tilt_sensor2" },
+};
+
+static struct gpio_tilt_state sg060_tilt_states[] = {
+	{
+		.gpios = (0 << 1) | (0 << 0),
+		.axes = (int[]) {
+			0,
+		},
+	}, {
+		.gpios = (0 << 1) | (1 << 0),
+		.axes = (int[]) {
+			1, /* 90 degrees */
+		},
+	}, {
+		.gpios = (1 << 1) | (1 << 0),
+		.axes = (int[]) {
+			2, /* 180 degrees */
+		},
+	}, {
+		.gpios = (1 << 1) | (0 << 0),
+		.axes = (int[]) {
+			3, /* 270 degrees */
+		},
+	},
+};
+
+static struct gpio_tilt_axis sg060_tilt_axes[] = {
+	{
+		.axis = ABS_RY,
+		.min = 0,
+		.max = 3,
+		.fuzz = 0,
+		.flat = 0,
+	},
+};
+
+static struct gpio_tilt_platform_data sg060_tilt_pdata= {
+	.gpios = sg060_tilt_gpios,
+	.nr_gpios = ARRAY_SIZE(sg060_tilt_gpios),
+
+	.axes = sg060_tilt_axes,
+	.nr_axes = ARRAY_SIZE(sg060_tilt_axes),
+
+	.states = sg060_tilt_states,
+	.nr_states = ARRAY_SIZE(sg060_tilt_states),
+
+	.debounce_interval = 100,
+
+	.poll_interval = 1000,
+	.enable = sg060_tilt_enable,
+	.disable = sg060_tilt_disable,
+};
+
+static struct platform_device sg060_device_tilt = {
+	.name = "gpio-tilt-polled",
+	.id = -1,
+	.dev = {
+		.platform_data = &sg060_tilt_pdata,
+	},
+};