drivers/input/misc/gpio_decoder.c

/*
 * 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.
 *
 * A generic driver to read multiple gpio lines and translate the
 * encoded numeric value into an input event.
 */

#include <linux/device.h>
#include <linux/gpio/consumer.h>
#include <linux/input.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>

struct gpio_decoder {
	struct gpio_descs *input_gpios;
	struct device *dev;
	u32 axis;
	u32 last_stable;
};

static 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]);
		if (val < 0) {
			dev_err(decoder->dev,
				"Error reading gpio %d: %d\n",
				desc_to_gpio(gpios->desc[i]), val);
			return val;
		}

		val = !!val;
		ret = (ret << 1) | val;
	}

	return ret;
}

static void gpio_decoder_poll_gpios(struct input_dev *input)
{
	struct gpio_decoder *decoder = input_get_drvdata(input);
	int state;

	state = gpio_decoder_get_gpios_state(decoder);
	if (state >= 0 && state != decoder->last_stable) {
		input_report_abs(input, decoder->axis, state);
		input_sync(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_dev *input;
	u32  max;
	int err;

	decoder = devm_kzalloc(dev, sizeof(*decoder), GFP_KERNEL);
	if (!decoder)
		return -ENOMEM;

	decoder->dev = dev;
	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;
	}

	if (device_property_read_u32(dev, "decoder-max-value", &max))
		max = (1U << decoder->input_gpios->ndescs) - 1;

	input = devm_input_allocate_device(dev);
	if (!input)
		return -ENOMEM;

	input_set_drvdata(input, decoder);

	input->name = pdev->name;
	input->id.bustype = BUS_HOST;
	input_set_abs_params(input, decoder->axis, 0, max, 0, 0);

	err = input_setup_polling(input, gpio_decoder_poll_gpios);
	if (err) {
		dev_err(dev, "failed to set up polling\n");
		return err;
	}

	err = input_register_device(input);
	if (err) {
		dev_err(dev, "failed to register input device\n");
		return err;
	}

	return 0;
}

#ifdef CONFIG_OF
static const struct of_device_id gpio_decoder_of_match[] = {
	{ .compatible = "gpio-decoder", },
	{ },
};
MODULE_DEVICE_TABLE(of, gpio_decoder_of_match);
#endif

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@ti.com>");
MODULE_LICENSE("GPL v2");