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// SPDX-License-Identifier: GPL-2.0-only
/*
* GPIO driven charlieplex keypad driver
*
* Copyright (c) 2026 Hugo Villeneuve <hvilleneuve@dimonoff.com>
*
* Based on matrix_keyboard.c
*/
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/dev_printk.h>
#include <linux/device/devres.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/input.h>
#include <linux/input/matrix_keypad.h>
#include <linux/math.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/string_helpers.h>
#include <linux/types.h>
struct charlieplex_keypad {
struct input_dev *input_dev;
struct gpio_descs *line_gpios;
unsigned int nlines;
unsigned int settling_time_us;
unsigned int debounce_threshold;
unsigned int debounce_count;
int debounce_code;
int current_code;
};
static void charlieplex_keypad_report_key(struct input_dev *input)
{
struct charlieplex_keypad *keypad = input_get_drvdata(input);
const unsigned short *keycodes = input->keycode;
if (keypad->current_code > 0) {
input_event(input, EV_MSC, MSC_SCAN, keypad->current_code);
input_report_key(input, keycodes[keypad->current_code], 0);
input_sync(input);
}
if (keypad->debounce_code) {
input_event(input, EV_MSC, MSC_SCAN, keypad->debounce_code);
input_report_key(input, keycodes[keypad->debounce_code], 1);
input_sync(input);
}
keypad->current_code = keypad->debounce_code;
}
static void charlieplex_keypad_check_switch_change(struct input_dev *input,
unsigned int code)
{
struct charlieplex_keypad *keypad = input_get_drvdata(input);
if (code != keypad->debounce_code) {
keypad->debounce_count = 0;
keypad->debounce_code = code;
}
if (keypad->debounce_code != keypad->current_code) {
if (keypad->debounce_count++ >= keypad->debounce_threshold)
charlieplex_keypad_report_key(input);
}
}
static int charlieplex_keypad_scan_line(struct charlieplex_keypad *keypad,
unsigned int oline)
{
struct gpio_descs *line_gpios = keypad->line_gpios;
DECLARE_BITMAP(values, MATRIX_MAX_ROWS);
int err;
/* Activate only one line as output at a time. */
gpiod_direction_output(line_gpios->desc[oline], 1);
if (keypad->settling_time_us)
fsleep(keypad->settling_time_us);
/* Read input on all other lines. */
err = gpiod_get_array_value_cansleep(line_gpios->ndescs, line_gpios->desc,
line_gpios->info, values);
gpiod_direction_input(line_gpios->desc[oline]);
if (err)
return err;
for (unsigned int iline = 0; iline < keypad->nlines; iline++) {
if (iline == oline)
continue; /* Do not read active output line. */
/* Check if GPIO is asserted. */
if (test_bit(iline, values))
return MATRIX_SCAN_CODE(oline, iline,
get_count_order(keypad->nlines));
}
return 0;
}
static void charlieplex_keypad_poll(struct input_dev *input)
{
struct charlieplex_keypad *keypad = input_get_drvdata(input);
int code = 0;
for (unsigned int oline = 0; oline < keypad->nlines; oline++) {
code = charlieplex_keypad_scan_line(keypad, oline);
if (code != 0)
break;
}
if (code >= 0)
charlieplex_keypad_check_switch_change(input, code);
}
static int charlieplex_keypad_init_gpio(struct platform_device *pdev,
struct charlieplex_keypad *keypad)
{
char **pin_names;
char label[32];
snprintf(label, sizeof(label), "%s-pin", pdev->name);
keypad->line_gpios = devm_gpiod_get_array(&pdev->dev, "line", GPIOD_IN);
if (IS_ERR(keypad->line_gpios))
return PTR_ERR(keypad->line_gpios);
keypad->nlines = keypad->line_gpios->ndescs;
if (keypad->nlines > MATRIX_MAX_ROWS)
return -EINVAL;
pin_names = devm_kasprintf_strarray(&pdev->dev, label, keypad->nlines);
if (IS_ERR(pin_names))
return PTR_ERR(pin_names);
for (unsigned int i = 0; i < keypad->line_gpios->ndescs; i++)
gpiod_set_consumer_name(keypad->line_gpios->desc[i], pin_names[i]);
return 0;
}
static int charlieplex_keypad_probe(struct platform_device *pdev)
{
struct charlieplex_keypad *keypad;
struct input_dev *input_dev;
unsigned int debounce_interval_ms = 5;
unsigned int poll_interval_ms;
int err;
keypad = devm_kzalloc(&pdev->dev, sizeof(*keypad), GFP_KERNEL);
if (!keypad)
return -ENOMEM;
input_dev = devm_input_allocate_device(&pdev->dev);
if (!input_dev)
return -ENOMEM;
keypad->input_dev = input_dev;
err = device_property_read_u32(&pdev->dev, "poll-interval", &poll_interval_ms);
if (err)
return dev_err_probe(&pdev->dev, err,
"failed to parse 'poll-interval' property\n");
if (poll_interval_ms == 0)
return dev_err_probe(&pdev->dev, -EINVAL, "invalid 'poll-interval' value\n");
device_property_read_u32(&pdev->dev, "debounce-delay-ms", &debounce_interval_ms);
device_property_read_u32(&pdev->dev, "settling-time-us", &keypad->settling_time_us);
keypad->current_code = -1;
keypad->debounce_code = -1;
keypad->debounce_threshold = DIV_ROUND_UP(debounce_interval_ms, poll_interval_ms);
err = charlieplex_keypad_init_gpio(pdev, keypad);
if (err)
return err;
input_dev->name = pdev->name;
input_dev->id.bustype = BUS_HOST;
err = matrix_keypad_build_keymap(NULL, NULL, keypad->nlines,
keypad->nlines, NULL, input_dev);
if (err)
return dev_err_probe(&pdev->dev, err, "failed to build keymap\n");
if (device_property_read_bool(&pdev->dev, "autorepeat"))
__set_bit(EV_REP, input_dev->evbit);
input_set_capability(input_dev, EV_MSC, MSC_SCAN);
err = input_setup_polling(input_dev, charlieplex_keypad_poll);
if (err)
return dev_err_probe(&pdev->dev, err, "unable to set up polling\n");
input_set_poll_interval(input_dev, poll_interval_ms);
input_set_drvdata(input_dev, keypad);
err = input_register_device(keypad->input_dev);
if (err)
return err;
return 0;
}
static const struct of_device_id charlieplex_keypad_dt_match[] = {
{ .compatible = "gpio-charlieplex-keypad" },
{ }
};
MODULE_DEVICE_TABLE(of, charlieplex_keypad_dt_match);
static struct platform_driver charlieplex_keypad_driver = {
.probe = charlieplex_keypad_probe,
.driver = {
.name = "charlieplex-keypad",
.of_match_table = charlieplex_keypad_dt_match,
},
};
module_platform_driver(charlieplex_keypad_driver);
MODULE_AUTHOR("Hugo Villeneuve <hvilleneuve@dimonoff.com>");
MODULE_DESCRIPTION("GPIO driven charlieplex keypad driver");
MODULE_LICENSE("GPL");
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