[PATCH v5 0/4] input: add GPIO-based charlieplex keypad

[PATCH v5 0/4] input: add GPIO-based charlieplex keypad

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

Hello,
this patch series add a new GPIO charlieplex keypad driver.

The first two patches simply commonize two properties that are present in
a few bindings, so that the actual patches for the charlieplex keypad driver
can reuse them instead of also redefining them.

I have tested the driver on a custom board with a Solidrun RZ/G2LC SOM
with three charlieplex keyboards, all connected thru a single PCAL6416 I2C GPIO
expander.

Link: [v1] https://lore.kernel.org/all/20260203155023.536103-1-hugo@hugovil.com/
Link: [v2] https://lore.kernel.org/all/20260213171431.2228814-1-hugo@hugovil.com/
Link: [v3] https://lore.kernel.org/all/20260225155409.612478-1-hugo@hugovil.com/
Link: [v4] https://lore.kernel.org/all/20260305192101.2125660-1-hugo@hugovil.com/

Changes for v5:
- Add Reviewed-by tags (Rob)
- Replace GPIO with line in settling-time-us property description (Rob)
- Reorder Makefile entry (Andy)
- Change copyright date to 2026 (Andy)
- Change some signed variables to unsigned (Andy)
- Move some variables declaration within loop (Andy)
- Add proper labels for GPIO pin names (Andy)

Changes for v4:
- Fix indentation in comments (Andy)
- Add missing includes (Andy)
- Remove OF dependency (Andy/Dmitry)
- Uniformize return code variables to "err" (Andy/Dmitry)
- Change signed iterator to unsigned and move within loop (Andy)
- Remove unused platform_set_drvdata() (Andy)
- Fixed typo in cover letter PCAL6416 (Geert)
- Changed name in bindings example (Geert)
- Added pull resistors to bindings doc and example (Geert)

Changes for v3:
- Add ASCII diagram in bindings, and reference to it in example
- Reorder properties alphabetically
- Add patch to define common input settling-time-us property
- Add patch to define common input debounce-delay-ms property

Changes for v2:
- Fix yamllint error for example
- Remove unused debug variable (nkeys)
- Remove support for custom linux,no-autorepeat DT property
- Remove support for custom gpio-activelow DT property

Thank you.

Hugo Villeneuve (4):
  dt-bindings: input: add debounce-delay-ms common property
  dt-bindings: input: add settling-time-us common property
  dt-bindings: input: add GPIO charlieplex keypad
  Input: charlieplex_keypad: add GPIO charlieplex keypad

 .../bindings/auxdisplay/holtek,ht16k33.yaml   |   5 +-
 .../bindings/input/cirrus,ep9307-keypad.yaml  |   7 +-
 .../input/gpio-charlieplex-keypad.yaml        | 108 +++++++++
 .../bindings/input/gpio-matrix-keypad.yaml    |   5 +-
 .../devicetree/bindings/input/input.yaml      |  16 ++
 .../input/mediatek,mt6779-keypad.yaml         |   1 +
 .../devicetree/bindings/mfd/fsl,mc13xxx.yaml  |   2 -
 MAINTAINERS                                   |   7 +
 drivers/input/keyboard/Kconfig                |  14 ++
 drivers/input/keyboard/Makefile               |   1 +
 drivers/input/keyboard/charlieplex_keypad.c   | 223 ++++++++++++++++++
 11 files changed, 377 insertions(+), 12 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
 create mode 100644 drivers/input/keyboard/charlieplex_keypad.c


base-commit: 6d4b67a2a76a4ff2393fe88119ae4332821b82b4
-- 
2.47.3

[PATCH v5 1/4] dt-bindings: input: add debounce-delay-ms common property

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

A few bindings are already defining a debounce-delay-ms property, so
add it to the input binding to reduce redundant redefines.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
---
 .../devicetree/bindings/auxdisplay/holtek,ht16k33.yaml    | 5 ++---
 .../devicetree/bindings/input/cirrus,ep9307-keypad.yaml   | 7 +++----
 .../devicetree/bindings/input/gpio-matrix-keypad.yaml     | 5 ++---
 Documentation/devicetree/bindings/input/input.yaml        | 8 ++++++++
 .../devicetree/bindings/input/mediatek,mt6779-keypad.yaml | 1 +
 Documentation/devicetree/bindings/mfd/fsl,mc13xxx.yaml    | 2 --
 6 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml b/Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml
index b90eec2077b4b..c46a2471f8b10 100644
--- a/Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml
+++ b/Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml
@@ -10,6 +10,7 @@ maintainers:
   - Robin van der Gracht <robin@protonic.nl>
 
 allOf:
+  - $ref: /schemas/input/input.yaml#
   - $ref: /schemas/input/matrix-keymap.yaml#
 
 properties:
@@ -33,9 +34,7 @@ properties:
   interrupts:
     maxItems: 1
 
-  debounce-delay-ms:
-    maxItems: 1
-    description: Debouncing interval time in milliseconds
+  debounce-delay-ms: true
 
   linux,keymap: true
 
diff --git a/Documentation/devicetree/bindings/input/cirrus,ep9307-keypad.yaml b/Documentation/devicetree/bindings/input/cirrus,ep9307-keypad.yaml
index a0d2460c55ab6..25b8b29c87d70 100644
--- a/Documentation/devicetree/bindings/input/cirrus,ep9307-keypad.yaml
+++ b/Documentation/devicetree/bindings/input/cirrus,ep9307-keypad.yaml
@@ -10,6 +10,7 @@ maintainers:
   - Alexander Sverdlin <alexander.sverdlin@gmail.com>
 
 allOf:
+  - $ref: input.yaml#
   - $ref: /schemas/input/matrix-keymap.yaml#
 
 description:
@@ -37,10 +38,8 @@ properties:
   clocks:
     maxItems: 1
 
-  debounce-delay-ms:
-    description: |
-          Time in microseconds that key must be pressed or
-          released for state change interrupt to trigger.
+  # Time for state change interrupt to trigger
+  debounce-delay-ms: true
 
   cirrus,prescale:
     description: row/column counter pre-scaler load value
diff --git a/Documentation/devicetree/bindings/input/gpio-matrix-keypad.yaml b/Documentation/devicetree/bindings/input/gpio-matrix-keypad.yaml
index ebfff9e42a365..69df24a5ae701 100644
--- a/Documentation/devicetree/bindings/input/gpio-matrix-keypad.yaml
+++ b/Documentation/devicetree/bindings/input/gpio-matrix-keypad.yaml
@@ -18,6 +18,7 @@ description:
   report the event using GPIO interrupts to the cpu.
 
 allOf:
+  - $ref: input.yaml#
   - $ref: /schemas/input/matrix-keymap.yaml#
 
 properties:
@@ -46,9 +47,7 @@ properties:
       Force GPIO polarity to active low.
       In the absence of this property GPIOs are treated as active high.
 
-  debounce-delay-ms:
-    description: Debounce interval in milliseconds.
-    default: 0
+  debounce-delay-ms: true
 
   col-scan-delay-us:
     description:
diff --git a/Documentation/devicetree/bindings/input/input.yaml b/Documentation/devicetree/bindings/input/input.yaml
index 94f7942189e8c..502e0b7eb500a 100644
--- a/Documentation/devicetree/bindings/input/input.yaml
+++ b/Documentation/devicetree/bindings/input/input.yaml
@@ -14,6 +14,14 @@ properties:
     description: Enable autorepeat when key is pressed and held down.
     type: boolean
 
+  debounce-delay-ms:
+    description:
+      Debounce delay in milliseconds. This is the time during which the key
+      press or release signal must remain stable before it is considered valid.
+    minimum: 0
+    maximum: 999
+    default: 0
+
   linux,keycodes:
     description:
       Specifies an array of numeric keycode values to be used for reporting
diff --git a/Documentation/devicetree/bindings/input/mediatek,mt6779-keypad.yaml b/Documentation/devicetree/bindings/input/mediatek,mt6779-keypad.yaml
index e365413732e7b..914dd3283df33 100644
--- a/Documentation/devicetree/bindings/input/mediatek,mt6779-keypad.yaml
+++ b/Documentation/devicetree/bindings/input/mediatek,mt6779-keypad.yaml
@@ -10,6 +10,7 @@ maintainers:
   - Mattijs Korpershoek <mkorpershoek@kernel.org>
 
 allOf:
+  - $ref: input.yaml#
   - $ref: /schemas/input/matrix-keymap.yaml#
 
 description: |
diff --git a/Documentation/devicetree/bindings/mfd/fsl,mc13xxx.yaml b/Documentation/devicetree/bindings/mfd/fsl,mc13xxx.yaml
index d2886f2686a8d..542ba51144243 100644
--- a/Documentation/devicetree/bindings/mfd/fsl,mc13xxx.yaml
+++ b/Documentation/devicetree/bindings/mfd/fsl,mc13xxx.yaml
@@ -76,8 +76,6 @@ properties:
           debounce-delay-ms:
             enum: [0, 30, 150, 750]
             default: 30
-            description:
-              Sets the debouncing delay in milliseconds.
 
           active-low:
             description: Set active when pin is pulled low.
-- 
2.47.3

[PATCH v5 2/4] dt-bindings: input: add settling-time-us common property

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

Add common property that can be reused by other bindings.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
---
 Documentation/devicetree/bindings/input/input.yaml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/input/input.yaml b/Documentation/devicetree/bindings/input/input.yaml
index 502e0b7eb500a..64d1c46cb2f2a 100644
--- a/Documentation/devicetree/bindings/input/input.yaml
+++ b/Documentation/devicetree/bindings/input/input.yaml
@@ -66,6 +66,14 @@ properties:
       reset automatically. Device with key pressed reset feature can specify
       this property.
 
+  settling-time-us:
+    description:
+      Delay, in microseconds, when activating an output line/col/row before
+      we can reliably read other input lines that maybe affected by this
+      output. This can be the case for an output with a RC circuit that affects
+      ramp-up/down times.
+    default: 0
+
 dependencies:
   linux,input-type: [ "linux,code" ]
 
-- 
2.47.3

[PATCH v5 3/4] dt-bindings: input: add GPIO charlieplex keypad

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

Add DT bindings for GPIO charlieplex keypad.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
---
 .../input/gpio-charlieplex-keypad.yaml        | 108 ++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml

diff --git a/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml b/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
new file mode 100644
index 0000000000000..c085de6dab854
--- /dev/null
+++ b/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
@@ -0,0 +1,108 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+
+$id: http://devicetree.org/schemas/input/gpio-charlieplex-keypad.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: GPIO charlieplex keypad
+
+maintainers:
+  - Hugo Villeneuve <hvilleneuve@dimonoff.com>
+
+description: |
+  The charlieplex keypad supports N^2)-N different key combinations (where N is
+  the number of I/O lines). Key presses and releases are detected by configuring
+  only one line as output at a time, and reading other line states. This process
+  is repeated for each line. Diodes are required to ensure current flows in only
+  one direction between any pair of pins, as well as pull-up or pull-down
+  resistors on all I/O lines.
+  This mechanism doesn't allow to detect simultaneous key presses.
+
+  Wiring example for 3 lines keyboard with 6 switches and 3 diodes (pull-up/down
+  resistors not shown but needed on L0, L1 and L2):
+
+  L0  --+---------------------+----------------------+
+        |                     |                      |
+  L1  -------+-----------+---------------------+     |
+        |    |           |    |                |     |
+  L2  -------------+----------------+-----+    |     |
+        |    |     |     |    |     |     |    |     |
+        |    |     |     |    |     |     |    |     |
+        |  S1 \  S2 \    |  S3 \  S4 \    |  S5 \  S6 \
+        |    |     |     |    |     |     |    |     |
+        |    +--+--+     |    +--+--+     |    +--+--+
+        |       |        |       |        |       |
+        |    D1 v        |    D2 v        |    D3 v
+        |       - (k)    |       - (k)    |       - (k)
+        |       |        |       |        |       |
+        +-------+        +-------+        +-------+
+
+  L: GPIO line
+  S: switch
+  D: diode (k indicates cathode)
+
+allOf:
+  - $ref: input.yaml#
+  - $ref: /schemas/input/matrix-keymap.yaml#
+
+properties:
+  compatible:
+    const: gpio-charlieplex-keypad
+
+  autorepeat: true
+
+  debounce-delay-ms:
+    default: 5
+
+  line-gpios:
+    description:
+      List of GPIOs used as lines. The gpio specifier for this property
+      depends on the gpio controller to which these lines are connected.
+
+  linux,keymap: true
+
+  poll-interval: true
+
+  settling-time-us: true
+
+  wakeup-source: true
+
+required:
+  - compatible
+  - line-gpios
+  - linux,keymap
+  - poll-interval
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/input/input.h>
+
+    keyboard {
+        compatible = "gpio-charlieplex-keypad";
+        debounce-delay-ms = <20>;
+        poll-interval = <5>;
+        settling-time-us = <2>;
+
+        line-gpios = <&gpio2 25 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)
+                      &gpio2 26 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)
+                      &gpio2 27 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>;
+
+        /* MATRIX_KEY(output, input, key-code) */
+        linux,keymap = <
+            /*
+             * According to wiring diagram above, if L1 is configured as
+             * output and HIGH, and we detect a HIGH level on input L0,
+             * then it means S1 is pressed: MATRIX_KEY(L1, L0, KEY...)
+             */
+            MATRIX_KEY(1, 0, KEY_F1) /* S1 */
+            MATRIX_KEY(2, 0, KEY_F2) /* S2 */
+            MATRIX_KEY(0, 1, KEY_F3) /* S3 */
+            MATRIX_KEY(2, 1, KEY_F4) /* S4 */
+            MATRIX_KEY(1, 2, KEY_F5) /* S5 */
+            MATRIX_KEY(0, 2, KEY_F6) /* S6 */
+        >;
+    };
-- 
2.47.3

[PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@dimonoff.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@dimonoff.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@dimonoff.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@canonical.com>
 M:	Joe Perches <joe@perches.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..60bb7baf802f7 100644
--- a/drivers/input/keyboard/Makefile
+++ b/drivers/input/keyboard/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_KEYBOARD_ATARI)		+= atakbd.o
 obj-$(CONFIG_KEYBOARD_ATKBD)		+= atkbd.o
 obj-$(CONFIG_KEYBOARD_BCM)		+= bcm-keypad.o
 obj-$(CONFIG_KEYBOARD_CAP11XX)		+= cap11xx.o
+obj-$(CONFIG_KEYBOARD_CHARLIEPLEX)	+= charlieplex_keypad.o
 obj-$(CONFIG_KEYBOARD_CLPS711X)		+= clps711x-keypad.o
 obj-$(CONFIG_KEYBOARD_CROS_EC)		+= cros_ec_keyb.o
 obj-$(CONFIG_KEYBOARD_CYPRESS_SF)	+= cypress-sf.o
diff --git a/drivers/input/keyboard/charlieplex_keypad.c b/drivers/input/keyboard/charlieplex_keypad.c
new file mode 100644
index 0000000000000..7064c40e1d839
--- /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) 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);
+	}
+
+	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 code;
+
+	code = 0;
+	for (unsigned int oline = 0; oline < keypad->nlines; oline++) {
+		DECLARE_BITMAP(values, MATRIX_MAX_ROWS);
+		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 (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)) {
+				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)
+{
+	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;
+	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, "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;
+
+	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");
-- 
2.47.3

Re: [PATCH v5 0/4] input: add GPIO-based charlieplex keypad

[Andy Shevchenko]

On Thu, Mar 12, 2026 at 02:00:54PM -0400, Hugo Villeneuve wrote:

> Hello, this patch series add a new GPIO charlieplex keypad driver.
> 
> The first two patches simply commonize two properties that are present in
> a few bindings, so that the actual patches for the charlieplex keypad driver
> can reuse them instead of also redefining them.
> 
> I have tested the driver on a custom board with a Solidrun RZ/G2LC SOM
> with three charlieplex keyboards, all connected thru a single PCAL6416 I2C GPIO
> expander.

Based on the review of this series I have a question to Dmitry.

Are we going to have Documentation/process/maintainer-input.rst with the
preferences of input subsystem in style and other undocumented things? When?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Andy Shevchenko]

On Thu, Mar 12, 2026 at 02:00:58PM -0400, 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.

LGTM,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Hugo Villeneuve]

Hi Dmitry,

On Fri, 13 Mar 2026 11:22:39 +0200
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Thu, Mar 12, 2026 at 02:00:58PM -0400, 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.
> 
> LGTM,
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

I was just wondering if this will go into v7.1, as I am not seing the
patch series in your input/next tree/branch for the moment? Let me know
if you need me to rebase it on v7.0.

-- 
Hugo Villeneuve

Re: [PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Dmitry Torokhov]

Hi Hugo,

On Thu, Mar 12, 2026 at 02:00:58PM -0400, Hugo Villeneuve wrote:
> +
> +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);

This needs input_sync() as otherwise userspace is free to only recognize
the last MSC_SCAN event.

> +	}
> +
> +	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) {

This does not work if debouncing is disabled (debounce threshold is 0).

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

We need to deactivate the line on error too.

> +
> +		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)) {
> +				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)
> +{
> +	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;
> +	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, "settling-time-us", &keypad->settling_time_us);

Not all of these are required properties. If they are missing the driver
will operate on garbage values.

> +
> +	keypad->current_code = -1;
> +	keypad->debounce_code = -1;
> +	keypad->debounce_threshold = DIV_ROUND_UP(debounce_interval_ms, poll_interval_ms);

This will bomb if poll interval is 0.

> +
> +	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");

Missing "return".

> +
> +	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");

Missing "return".

I fixed it up and applied, please take a look in my 'next' branch and
tell me if I messed up.

Thanks.

-- 
Dmitry

Re: [PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Hugo Villeneuve]

Hi Dmitry,

On Sun, 19 Apr 2026 21:47:40 -0700
Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:

> Hi Hugo,
> 
> On Thu, Mar 12, 2026 at 02:00:58PM -0400, Hugo Villeneuve wrote:
> > +
> > +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);
> 
> This needs input_sync() as otherwise userspace is free to only recognize
> the last MSC_SCAN event.

Ok, now I get it, my code would have been be working only if it was an
if/else.

> 
> > +	}
> > +
> > +	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) {
> 
> This does not work if debouncing is disabled (debounce threshold is 0).

Yes.


> 
> > +		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 code;
> > +
> > +	code = 0;
> > +	for (unsigned int oline = 0; oline < keypad->nlines; oline++) {
> > +		DECLARE_BITMAP(values, MATRIX_MAX_ROWS);
> > +		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;
> 
> We need to deactivate the line on error too.

Yer, good catch.

> 
> > +
> > +		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)) {
> > +				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)
> > +{
> > +	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;
> > +	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, "settling-time-us", &keypad->settling_time_us);
> 
> Not all of these are required properties. If they are missing the driver
> will operate on garbage values.

Yes.


> 
> > +
> > +	keypad->current_code = -1;
> > +	keypad->debounce_code = -1;
> > +	keypad->debounce_threshold = DIV_ROUND_UP(debounce_interval_ms, poll_interval_ms);
> 
> This will bomb if poll interval is 0.

Yes.

> 
> > +
> > +	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");
> 
> Missing "return".
> 
> > +
> > +	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");
> 
> Missing "return".

Ok for both.

> I fixed it up and applied, please take a look in my 'next' branch and
> tell me if I messed up.

Thank you for the review and the fixes.

I tested it on the real hardware and all is good.

So I imagine that it can still go into 7.1 since it is a new driver
and not a modification of an existing one?


-- 
Hugo Villeneuve

Re: [PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Dmitry Torokhov]

On Mon, Apr 20, 2026 at 11:01:59AM -0400, Hugo Villeneuve wrote:
> I tested it on the real hardware and all is good.

Thank you for testing the changes.

> 
> So I imagine that it can still go into 7.1 since it is a new driver
> and not a modification of an existing one?

Yes, since this is a new driver I will include it in 7.1 pull request.

Thanks.

-- 
Dmitry

Re: [PATCH v5 4/4] Input: charlieplex_keypad: add GPIO charlieplex keypad

[Hugo Villeneuve]

On Mon, 20 Apr 2026 10:16:02 -0700
Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:

> On Mon, Apr 20, 2026 at 11:01:59AM -0400, Hugo Villeneuve wrote:
> > I tested it on the real hardware and all is good.
> 
> Thank you for testing the changes.
> 
> > 
> > So I imagine that it can still go into 7.1 since it is a new driver
> > and not a modification of an existing one?
> 
> Yes, since this is a new driver I will include it in 7.1 pull request.
> 
> Thanks.

Great, thank you.

-- 
Hugo Villeneuve