[PATCH v3 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Andy Shevchenko]

On Wed, Feb 25, 2026 at 10:54:01AM -0500, Hugo Villeneuve wrote:

> Add support for GPIO-based charlieplex keypad, allowing to control
> N^2-N keys using N GPIO lines.
> 
> Reuse matrix keypad keymap to simplify, even if there is no concept
> of rows and columns in this type of keyboard.

...

> +/*
> + *  GPIO driven charlieplex keypad driver
> + *
> + *  Copyright (c) 2025 Hugo Villeneuve <hvilleneuve at dimonoff.com>
> + *
> + *  Based on matrix_keyboard.c

A single space after asterisk is enough.

> + */

...

+ bitops.h

> +#include <linux/delay.h>

+ dev_printk.h
+ device/devres.h
+ err.h

> +#include <linux/gpio/consumer.h>
> +#include <linux/input.h>
> +#include <linux/input/matrix_keypad.h>

+ math.h

> +#include <linux/module.h>

> +#include <linux/of.h>

Is this in use? Or you wanted mod_devicetable.h for OF ID table?

> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/types.h>

...

> +	for (code = 0, oline = 0; oline < keypad->nlines; oline++) {
> +		DECLARE_BITMAP(values, MATRIX_MAX_ROWS);
> +		int iline;

> +		int rc;

I think Dmitry prefers 'error' name for this kind of variables.

> +		/* Activate only one line as output at a time. */
> +		gpiod_direction_output(keypad->line_gpios->desc[oline], 1);
> +
> +		if (keypad->settling_time_us)
> +			fsleep(keypad->settling_time_us);
> +
> +		/* Read input on all other lines. */
> +		rc = gpiod_get_array_value_cansleep(keypad->line_gpios->ndescs,
> +						    keypad->line_gpios->desc,
> +						    keypad->line_gpios->info, values);
> +		if (rc)
> +			return;
> +
> +		for (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)) {
> +				code = MATRIX_SCAN_CODE(oline, iline,
> +							get_count_order(keypad->nlines));
> +				/*
> +				 * Exit loop immediately since we cannot detect
> +				 * more than one key press at a time.
> +				 */
> +				break;
> +			}
> +		}
> +
> +		gpiod_direction_input(keypad->line_gpios->desc[oline]);
> +
> +		if (code)
> +			break;
> +	}

...

> +static int charlieplex_keypad_init_gpio(struct platform_device *pdev,
> +					struct charlieplex_keypad *keypad)
> +{
> +	int i;

Why signed? But see below as well.

> +	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;

> +	for (i = 0; i < keypad->nlines; i++)

iterator is local to the loop, hence

	for (unsigned int i = 0; i < keypad->nlines; i++)

> +		gpiod_set_consumer_name(keypad->line_gpios->desc[i], "charlieplex_kbd_line");
> +
> +	return 0;
> +}

...

> +static int charlieplex_keypad_probe(struct platform_device *pdev)
> +{
> +	struct charlieplex_keypad *keypad;
> +	unsigned int debounce_interval_ms;
> +	unsigned int poll_interval_ms;
> +	struct input_dev *input_dev;

> +	int err;

The naming is even inconsistent between the functions...

> +	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;
> +
> +	device_property_read_u32(&pdev->dev, "poll-interval", &poll_interval_ms);
> +	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)
> +		dev_err_probe(&pdev->dev, -ENOMEM, "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)
> +		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;

> +	platform_set_drvdata(pdev, keypad);

Is this needed?

> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko