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Message-ID: <20260203155023.536103-3-hugo@hugovil.com>
Date: Tue, 3 Feb 2026 10:49:48 -0500
From: Hugo Villeneuve <hugo@...ovil.com>
To: hvilleneuve@...onoff.com,
dmitry.torokhov@...il.com,
robh@...nel.org,
krzk+dt@...nel.org,
conor+dt@...nel.org
Cc: linux-input@...r.kernel.org,
devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org,
hugo@...ovil.com
Subject: [PATCH 2/2] Input: charlieplex_keypad: add GPIO charlieplex keypad
From: Hugo Villeneuve <hvilleneuve@...onoff.com>
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.
Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
MAINTAINERS | 7 +
drivers/input/keyboard/Kconfig | 14 ++
drivers/input/keyboard/Makefile | 1 +
drivers/input/keyboard/charlieplex_keypad.c | 223 ++++++++++++++++++++
4 files changed, 245 insertions(+)
create mode 100644 drivers/input/keyboard/charlieplex_keypad.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 9ed6d11a77466..0b2d71f32b400 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5765,6 +5765,13 @@ S: Maintained
F: Documentation/hwmon/powerz.rst
F: drivers/hwmon/powerz.c
+CHARLIEPLEX KEYPAD DRIVER
+M: Hugo Villeneuve <hvilleneuve@...onoff.com>
+S: Supported
+W: http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/electronic-circuits/matrix-keypad-scan-decode
+F: Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
+F: drivers/input/keyboard/charlieplex_keypad.c
+
CHECKPATCH
M: Andy Whitcroft <apw@...onical.com>
M: Joe Perches <joe@...ches.com>
diff --git a/drivers/input/keyboard/Kconfig b/drivers/input/keyboard/Kconfig
index 2ff4fef322c24..ae54b4b7e2d8a 100644
--- a/drivers/input/keyboard/Kconfig
+++ b/drivers/input/keyboard/Kconfig
@@ -289,6 +289,20 @@ config KEYBOARD_MATRIX
To compile this driver as a module, choose M here: the
module will be called matrix_keypad.
+config KEYBOARD_CHARLIEPLEX
+ tristate "GPIO driven chearlieplex keypad support"
+ depends on GPIOLIB || COMPILE_TEST
+ select INPUT_MATRIXKMAP
+ help
+ Enable support for GPIO driven charlieplex keypad. A charlieplex
+ keypad allows to use fewer GPIO lines to interface to key switches.
+ For example, an N lines charlieplex keypad can be used to interface
+ to N^2-N different key switches. However, this type of keypad
+ cannot detect more than one key press at a time.
+
+ To compile this driver as a module, choose M here: the
+ module will be called charlieplex_keypad.
+
config KEYBOARD_HIL_OLD
tristate "HP HIL keyboard support (simple driver)"
depends on GSC || HP300
diff --git a/drivers/input/keyboard/Makefile b/drivers/input/keyboard/Makefile
index 2d906e14f3e27..40b5cf5d374d2 100644
--- 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-$(CONFIG_KEYBOARD_CHARLIEPLEX) += charlieplex_keypad.o
obj-$(CONFIG_KEYBOARD_MAX7359) += max7359_keypad.o
obj-$(CONFIG_KEYBOARD_MAX7360) += max7360-keypad.o
obj-$(CONFIG_KEYBOARD_MPR121) += mpr121_touchkey.o
diff --git a/drivers/input/keyboard/charlieplex_keypad.c b/drivers/input/keyboard/charlieplex_keypad.c
new file mode 100644
index 0000000000000..f9d6f5ecfa8dc
--- /dev/null
+++ b/drivers/input/keyboard/charlieplex_keypad.c
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * GPIO driven charlieplex keypad driver
+ *
+ * Copyright (c) 2025 Hugo Villeneuve <hvilleneuve@...onoff.com>
+ *
+ * Based on matrix_keyboard.c
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/input.h>
+#include <linux/input/matrix_keypad.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/types.h>
+
+struct charlieplex_keypad {
+ struct input_dev *input_dev;
+ struct gpio_descs *line_gpios;
+ unsigned int nlines;
+ unsigned int line_scan_delay_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);
+ }
+
+ 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,
+ int code)
+{
+ struct charlieplex_keypad *keypad = input_get_drvdata(input);
+
+ if (code != keypad->debounce_code) {
+ keypad->debounce_count = 0;
+ keypad->debounce_code = code;
+ } else if (keypad->debounce_count < keypad->debounce_threshold) {
+ keypad->debounce_count++;
+
+ if (keypad->debounce_count >= keypad->debounce_threshold &&
+ keypad->debounce_code != keypad->current_code)
+ charlieplex_keypad_report_key(input);
+ }
+}
+
+static void charlieplex_keypad_poll(struct input_dev *input)
+{
+ struct charlieplex_keypad *keypad = input_get_drvdata(input);
+ int oline;
+ int code;
+
+ for (code = 0, oline = 0; oline < keypad->nlines; oline++) {
+ DECLARE_BITMAP(values, MATRIX_MAX_ROWS);
+ int iline;
+ int rc;
+
+ /* Activate only one line as output at a time. */
+ gpiod_direction_output(keypad->line_gpios->desc[oline], 1);
+
+ if (keypad->line_scan_delay_us)
+ fsleep(keypad->line_scan_delay_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;
+ }
+
+ charlieplex_keypad_check_switch_change(input, code);
+}
+
+static int charlieplex_keypad_init_gpio(struct platform_device *pdev,
+ struct charlieplex_keypad *keypad)
+{
+ bool active_low;
+ int nkeys;
+ int i;
+
+ 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;
+
+ nkeys = (keypad->nlines * keypad->nlines) - keypad->nlines;
+
+ active_low = device_property_read_bool(&pdev->dev, "gpio-activelow");
+
+ for (i = 0; i < keypad->nlines; i++) {
+ gpiod_set_consumer_name(keypad->line_gpios->desc[i], "charlieplex_kbd_line");
+
+ if (active_low ^ gpiod_is_active_low(keypad->line_gpios->desc[i]))
+ gpiod_toggle_active_low(keypad->line_gpios->desc[i]);
+ }
+
+ 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;
+
+ 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, "line-scan-delay-us", &keypad->line_scan_delay_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, "linux,no-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);
+
+ 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 = of_match_ptr(charlieplex_keypad_dt_match),
+ },
+};
+module_platform_driver(charlieplex_keypad_driver);
+
+MODULE_AUTHOR("Hugo Villeneuve <hvilleneuve@...onoff.com>");
+MODULE_DESCRIPTION("GPIO driven charlieplex keypad driver");
+MODULE_LICENSE("GPL");
--
2.47.3
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