[PATCH v4 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Andy Shevchenko]

On Thu, Mar 05, 2026 at 02:20:50PM -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.

...

> --- a/drivers/input/keyboard/Makefile
> +++ b/drivers/input/keyboard/Makefile
> @@ -40,6 +40,7 @@ obj-$(CONFIG_KEYBOARD_LOCOMO)		+= locomokbd.o
>  obj-$(CONFIG_KEYBOARD_LPC32XX)		+= lpc32xx-keys.o
>  obj-$(CONFIG_KEYBOARD_MAPLE)		+= maple_keyb.o
>  obj-$(CONFIG_KEYBOARD_MATRIX)		+= matrix_keypad.o
> +obj-$(CONFIG_KEYBOARD_CHARLIEPLEX)	+= charlieplex_keypad.o

Seem unordered. At least the all around it is ordered AFAICS.

>  obj-$(CONFIG_KEYBOARD_MAX7359)		+= max7359_keypad.o
>  obj-$(CONFIG_KEYBOARD_MAX7360)		+= max7360-keypad.o
>  obj-$(CONFIG_KEYBOARD_MPR121)		+= mpr121_touchkey.o

...

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

2026?

> + *
> + * 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/types.h>

> +static void charlieplex_keypad_poll(struct input_dev *input)
> +{
> +	struct charlieplex_keypad *keypad = input_get_drvdata(input);

> +	int oline;

Why signed?

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

Can be like

	code = 0;
	for (unsigned int oline = 0; oline < keypad->nlines; oline++) {

as iterator is not used outside the loop.

> +		DECLARE_BITMAP(values, MATRIX_MAX_ROWS);

> +		int iline;

Why signed?

> +		int err;
> +
> +		/* 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. */
> +		err = gpiod_get_array_value_cansleep(keypad->line_gpios->ndescs,
> +						     keypad->line_gpios->desc,
> +						     keypad->line_gpios->info, values);
> +		if (err)
> +			return;

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

Can be just

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

as iterator is not used outside the loop.

> +			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;
> +	}
> +
> +	charlieplex_keypad_check_switch_change(input, code);
> +}

...

> +	for (unsigned int i = 0; i < keypad->nlines; i++)
> +		gpiod_set_consumer_name(keypad->line_gpios->desc[i], "charlieplex_kbd_line");

Hmm... Don't you want to give it an index?

(In case you go this direction, see the kasprintf_strarray() or
 its managed variant.)

-- 
With Best Regards,
Andy Shevchenko