input: add arduino,modulino-buttons

Add an input driver for the modulino buttons module. This is a pluggable
I2C board implementing three buttons and three LEDs, the I2C protocol is
implemented on a microcontroller on the modulino board itself, the
firmware for that is open source and can be updated using an Arduino
sketch:

Link: https://github.com/arduino/node_modulino_firmware
Link: https://github.com/arduino-libraries/Modulino
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

drivers/input/CMakeLists.txt

@@ -23,6 +23,7 @@ zephyr_library_sources_ifdef(CONFIG_INPUT_ITE_IT51XXX_KBD input_ite_it51xxx_kbd.
 zephyr_library_sources_ifdef(CONFIG_INPUT_ITE_IT8801_KBD input_ite_it8801_kbd.c)
 zephyr_library_sources_ifdef(CONFIG_INPUT_ITE_IT8XXX2_KBD input_ite_it8xxx2_kbd.c)
 zephyr_library_sources_ifdef(CONFIG_INPUT_KBD_MATRIX input_kbd_matrix.c)
+zephyr_library_sources_ifdef(CONFIG_INPUT_MODULINO_BUTTONS input_modulino_buttons.c)
 zephyr_library_sources_ifdef(CONFIG_INPUT_NPCX_KBD input_npcx_kbd.c)
 zephyr_library_sources_ifdef(CONFIG_INPUT_NUNCHUK input_nunchuk.c)
 zephyr_library_sources_ifdef(CONFIG_INPUT_PAT912X input_pat912x.c)

drivers/input/Kconfig

@@ -25,6 +25,7 @@ source "drivers/input/Kconfig.it51xxx"
 source "drivers/input/Kconfig.it8801"
 source "drivers/input/Kconfig.it8xxx2"
 source "drivers/input/Kconfig.kbd_matrix"
+source "drivers/input/Kconfig.modulino"
 source "drivers/input/Kconfig.npcx"
 source "drivers/input/Kconfig.nunchuk"
 source "drivers/input/Kconfig.pat912x"

drivers/input/Kconfig.modulino

@@ -0,0 +1,10 @@
+# Copyright (c) 2025 Google, LLC
+# SPDX-License-Identifier: Apache-2.0
+
+config INPUT_MODULINO_BUTTONS
+	bool "Arduino Modulino buttons"
+	default y
+	depends on DT_HAS_ARDUINO_MODULINO_BUTTONS_ENABLED
+	select I2C
+	help
+	  Enable driver Arduino Modulino Buttons.

drivers/input/input_modulino_buttons.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT arduino_modulino_buttons
+
+#include <zephyr/device.h>
+#include <zephyr/drivers/i2c.h>
+#include <zephyr/input/input.h>
+#include <zephyr/kernel.h>
+#include <zephyr/logging/log.h>
+
+LOG_MODULE_REGISTER(modulino_buttons, CONFIG_INPUT_LOG_LEVEL);
+
+#define MODULINO_NUM_BUTTONS 3
+
+struct modulino_buttons_config {
+	struct i2c_dt_spec bus;
+	uint32_t poll_period_ms;
+	uint32_t zephyr_code[MODULINO_NUM_BUTTONS];
+};
+
+struct modulino_buttons_data {
+	const struct device *dev;
+	struct k_work_delayable poll_work;
+	uint8_t prev_state[MODULINO_NUM_BUTTONS];
+};
+
+static void modulino_buttons_handler(struct k_work *work)
+{
+	struct k_work_delayable *dwork = k_work_delayable_from_work(work);
+	struct modulino_buttons_data *data = CONTAINER_OF(
+			dwork, struct modulino_buttons_data, poll_work);
+	const struct device *dev = data->dev;
+	const struct modulino_buttons_config *cfg = dev->config;
+	int ret;
+	uint8_t buf[MODULINO_NUM_BUTTONS + 1];
+
+	ret = i2c_read_dt(&cfg->bus, buf, sizeof(buf));
+	if (ret < 0) {
+		LOG_ERR("i2c read error: %d", ret);
+		goto out;
+	}
+
+	for (uint8_t i = 0; i < MODULINO_NUM_BUTTONS; i++) {
+		uint8_t state = buf[i + 1];
+
+		if (data->prev_state[i] != state) {
+			input_report_key(dev, cfg->zephyr_code[i], state, true, K_FOREVER);
+		}
+	}
+
+	memcpy(data->prev_state, &buf[1], sizeof(data->prev_state));
+
+out:
+	k_work_reschedule(dwork, K_MSEC(cfg->poll_period_ms));
+}
+
+static int modulino_buttons_init(const struct device *dev)
+{
+	const struct modulino_buttons_config *cfg = dev->config;
+	struct modulino_buttons_data *data = dev->data;
+
+	data->dev = dev;
+
+	if (!i2c_is_ready_dt(&cfg->bus)) {
+		LOG_ERR("Bus device is not ready");
+		return -ENODEV;
+	}
+
+	k_work_init_delayable(&data->poll_work, modulino_buttons_handler);
+	k_work_reschedule(&data->poll_work, K_MSEC(cfg->poll_period_ms));
+
+	return 0;
+}
+
+#define MODULINO_BUTTONS_INIT(inst)							\
+	BUILD_ASSERT(DT_INST_PROP_LEN(inst, zephyr_codes) == MODULINO_NUM_BUTTONS,	\
+		     "zephyr,codes must specify three key codes");			\
+											\
+	static const struct modulino_buttons_config modulino_buttons_cfg_##inst = {	\
+		.bus = I2C_DT_SPEC_GET(DT_INST_PARENT(inst)),				\
+		.poll_period_ms = DT_INST_PROP(inst, poll_period_ms),			\
+		.zephyr_code = DT_INST_PROP(inst, zephyr_codes),			\
+	};										\
+											\
+	static struct modulino_buttons_data modulino_buttons_data_##inst;		\
+											\
+	DEVICE_DT_INST_DEFINE(inst, modulino_buttons_init, NULL,			\
+			      &modulino_buttons_data_##inst,				\
+			      &modulino_buttons_cfg_##inst,				\
+			      POST_KERNEL, CONFIG_INPUT_INIT_PRIORITY, NULL);
+
+
+DT_INST_FOREACH_STATUS_OKAY(MODULINO_BUTTONS_INIT)

dts/bindings/input/arduino,modulino-buttons.yaml

@@ -0,0 +1,20 @@
+# Copyright (c) 2025 Google, LLC
+# SPDX-License-Identifier: Apache-2.0
+
+description: Arduino Modulino buttons
+
+compatible: "arduino,modulino-buttons"
+
+properties:
+  zephyr,codes:
+    type: array
+    required: true
+    description: |
+      Key codes to emit, the module has three buttons so this must specify
+      three key codes.
+
+  poll-period-ms:
+    type: int
+    default: 50
+    description: |
+      How often to poll the buttons over the i2c bus, defaults to 50ms.