[PATCH 1/2] input: misc: Add generic input driver to read encoded GPIO lines

[Vignesh R]

Add a driver to read group of GPIO lines and provide its status as a
numerical value as input event to the system. This will help in
intefacing devices, that can be connected over GPIOs, that provide input
to the system by driving GPIO lines connected to them like a rotary dial
or a switch.

For example, a rotary switch can be connected to four GPIO lines. The
status of the GPIO lines reflect the actual position of the rotary
switch dial. For example, if dial points to 9, then the four GPIO lines
connected to the switch will read HLLH(0b'1001 = 9). This value
can be reported as an ABS_* event to the input subsystem.

Signed-off-by: Vignesh R <vigneshr@xxxxxx>
---
 .../devicetree/bindings/input/gpio-decoder.txt     |  23 ++++
 drivers/input/misc/Kconfig                         |  12 ++
 drivers/input/misc/Makefile                        |   1 +
 drivers/input/misc/gpio_decoder.c                  | 128 +++++++++++++++++++++
 4 files changed, 164 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/input/gpio-decoder.txt
 create mode 100644 drivers/input/misc/gpio_decoder.c

diff --git a/Documentation/devicetree/bindings/input/gpio-decoder.txt b/Documentation/devicetree/bindings/input/gpio-decoder.txt
new file mode 100644
index 000000000000..efd947f52cb3
--- /dev/null
+++ b/Documentation/devicetree/bindings/input/gpio-decoder.txt
@@ -0,0 +1,23 @@
+* GPIO Decoder DT bindings
+
+Required Properties:
+- compatible: should be "gpio-decoder"
+- gpios: a spec of gpios (atleast two) to be decoded to a number with
+  first entry representing the MSB.
+
+Optional Properties:
+- gpio-decoder,max-value: Maximum possible value that can be reported by
+  the gpios.
+- linux,axis: the input subsystem axis to map to (ABS_X/ABS_Y).
+  Defaults to 0 (ABS_X).
+
+Example:
+	gpio-decoder0 {
+		compatible = "gpio-decoder";
+		gpios = <&pca9536 3 GPIO_ACTIVE_HIGH>,
+			<&pca9536 2 GPIO_ACTIVE_HIGH>,
+			<&pca9536 1 GPIO_ACTIVE_HIGH>,
+			<&pca9536 0 GPIO_ACTIVE_HIGH>;
+		linux,axis = <0>; /* ABS_X */
+		gpio-decoder,max-value = <9>;
+	};
diff --git a/drivers/input/misc/Kconfig b/drivers/input/misc/Kconfig
index efb0ca871327..c44513cac3b7 100644
--- a/drivers/input/misc/Kconfig
+++ b/drivers/input/misc/Kconfig
@@ -292,6 +292,18 @@ config INPUT_GPIO_TILT_POLLED
 	  To compile this driver as a module, choose M here: the
 	  module will be called gpio_tilt_polled.
 
+config INPUT_GPIO_DECODER
+	tristate "Polled GPIO Decoder Input driver"
+	depends on GPIOLIB && OF
+	select INPUT_POLLDEV
+	help
+	 Say Y here if you want driver to read status of multiple GPIO
+	 lines and report the encoded value as an absolute integer to
+	 input subsystem.
+
+	 To compile this driver as a module, choose M here: the module
+	 will will be called gpio_decoder.
+
 config INPUT_IXP4XX_BEEPER
 	tristate "IXP4XX Beeper support"
 	depends on ARCH_IXP4XX
diff --git a/drivers/input/misc/Makefile b/drivers/input/misc/Makefile
index 6a1e5e20fc1c..0b6d025f0487 100644
--- a/drivers/input/misc/Makefile
+++ b/drivers/input/misc/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_INPUT_DRV2667_HAPTICS)	+= drv2667.o
 obj-$(CONFIG_INPUT_GP2A)		+= gp2ap002a00f.o
 obj-$(CONFIG_INPUT_GPIO_BEEPER)		+= gpio-beeper.o
 obj-$(CONFIG_INPUT_GPIO_TILT_POLLED)	+= gpio_tilt_polled.o
+obj-$(CONFIG_INPUT_GPIO_DECODER)	+= gpio_decoder.o
 obj-$(CONFIG_INPUT_HISI_POWERKEY)	+= hisi_powerkey.o
 obj-$(CONFIG_HP_SDC_RTC)		+= hp_sdc_rtc.o
 obj-$(CONFIG_INPUT_IMS_PCU)		+= ims-pcu.o
diff --git a/drivers/input/misc/gpio_decoder.c b/drivers/input/misc/gpio_decoder.c
new file mode 100644
index 000000000000..e3bed35fc8db
--- /dev/null
+++ b/drivers/input/misc/gpio_decoder.c
@@ -0,0 +1,128 @@
+/*
+ * gpio-decoder.c
+ *
+ * A generic driver to reads multiple gpio lines and translate the
+ * encoded numeric value into an input event.
+ *
+ * Copyright (C) 2016 Texas Instruments Incorporated - http://www.ti.com/
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation version 2.
+ *
+ * This program is distributed "as is" WITHOUT ANY WARRANTY of any
+ * kind, whether express or implied; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/input.h>
+#include <linux/input-polldev.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+struct gpio_decoder {
+	struct input_polled_dev *poll_dev;
+	struct gpio_descs *input_gpios;
+	struct device *dev;
+	u32 axis;
+	u32 last_stable;
+};
+
+static unsigned int gpio_decoder_get_gpios_state(struct gpio_decoder
+						 *decoder)
+{
+	struct gpio_descs *gpios = decoder->input_gpios;
+	unsigned int ret = 0;
+	int i, val;
+
+	for (i = 0; i < gpios->ndescs; i++) {
+		val = gpiod_get_value_cansleep(gpios->desc[i]);
+		ret = ret << 1 | val;
+	}
+
+	return ret;
+}
+
+static void gpio_decoder_poll_gpios(struct input_polled_dev *poll_dev)
+{
+	struct gpio_decoder *decoder = poll_dev->private;
+	unsigned int state = gpio_decoder_get_gpios_state(decoder);
+
+	if (state != decoder->last_stable) {
+		input_report_abs(poll_dev->input, decoder->axis, state);
+		input_sync(poll_dev->input);
+		decoder->last_stable = state;
+	}
+}
+
+static int gpio_decoder_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct gpio_decoder *decoder;
+	struct input_polled_dev *poll_dev;
+	u32  max;
+	int err;
+
+	decoder = devm_kzalloc(dev, sizeof(struct gpio_decoder), GFP_KERNEL);
+	if (!decoder)
+		return -ENOMEM;
+
+	device_property_read_u32(dev, "linux,axis", &decoder->axis);
+	decoder->input_gpios = devm_gpiod_get_array(dev, NULL, GPIOD_IN);
+	if (IS_ERR(decoder->input_gpios)) {
+		dev_err(dev, "unable to acquire input gpios\n");
+		return PTR_ERR(decoder->input_gpios);
+	}
+	if (decoder->input_gpios->ndescs < 2) {
+		dev_err(dev, "not enough gpios found\n");
+		return -EINVAL;
+	}
+	device_property_read_u32(dev, "gpio-decoder,max-value", &max);
+
+	decoder->dev = dev;
+	poll_dev = devm_input_allocate_polled_device(decoder->dev);
+	if (!poll_dev)
+		return -ENOMEM;
+
+	poll_dev->private = decoder;
+	poll_dev->poll = gpio_decoder_poll_gpios;
+	decoder->poll_dev = poll_dev;
+
+	poll_dev->input->name = pdev->name;
+	poll_dev->input->id.bustype = BUS_HOST;
+	poll_dev->input->dev.parent = dev;
+	input_set_abs_params(poll_dev->input, decoder->axis, 0, max, 0, 1);
+
+	err = input_register_polled_device(poll_dev);
+	if (err) {
+		dev_err(dev, "failed to register polled  device\n");
+		return err;
+	}
+	platform_set_drvdata(pdev, decoder);
+
+	return 0;
+}
+
+static const struct of_device_id gpio_decoder_of_match[] = {
+	{ .compatible = "gpio-decoder", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, gpio_decoder_of_match);
+
+static struct platform_driver gpio_decoder_driver = {
+	.probe		= gpio_decoder_probe,
+	.driver		= {
+		.name	= "gpio-decoder",
+		.of_match_table = of_match_ptr(gpio_decoder_of_match),
+	}
+};
+module_platform_driver(gpio_decoder_driver);
+
+MODULE_DESCRIPTION("GPIO decoder input driver");
+MODULE_AUTHOR("Vignesh R <vigneshr@xxxxxx>");
+MODULE_LICENSE("GPL v2");
-- 
2.9.2