feat(behaviors): Add soft off behavior.

* New soft-off behavior that can be used to force the device
  into  soft-off state with only certain configured wakeup
  devices.

app/CMakeLists.txt

@@ -55,6 +55,7 @@ if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
   target_sources(app PRIVATE src/behaviors/behavior_to_layer.c)
   target_sources(app PRIVATE src/behaviors/behavior_transparent.c)
   target_sources(app PRIVATE src/behaviors/behavior_none.c)
+  target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_SOFT_OFF app PRIVATE src/behaviors/behavior_soft_off.c)
   target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_SENSOR_ROTATE app PRIVATE src/behaviors/behavior_sensor_rotate.c)
   target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_SENSOR_ROTATE_VAR app PRIVATE src/behaviors/behavior_sensor_rotate_var.c)
   target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_SENSOR_ROTATE_COMMON app PRIVATE src/behaviors/behavior_sensor_rotate_common.c)

app/Kconfig.behaviors

@@ -16,6 +16,10 @@ config ZMK_BEHAVIOR_KEY_TOGGLE
     default y
     depends on DT_HAS_ZMK_BEHAVIOR_KEY_TOGGLE_ENABLED
 
+config ZMK_BEHAVIOR_SOFT_OFF
+    bool
+    default y
+    depends on DT_HAS_ZMK_BEHAVIOR_SOFT_OFF_ENABLED && ZMK_PM_SOFT_OFF
 
 config ZMK_BEHAVIOR_SENSOR_ROTATE_COMMON
     bool

app/dts/bindings/behaviors/zmk,behavior-soft-off.yaml

@@ -0,0 +1,14 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Soft-Off Behavior
+
+compatible: "zmk,behavior-soft-off"
+
+include: zero_param.yaml
+
+properties:
+  hold-time-ms:
+    type: int
+    required: false
+    description: Number of milliseconds the behavior must be held before releasing will actually trigger a soft-off.

app/src/behaviors/behavior_soft_off.c

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#define DT_DRV_COMPAT zmk_behavior_soft_off
+
+#include <zephyr/device.h>
+#include <drivers/behavior.h>
+#include <zephyr/logging/log.h>
+
+#include <zmk/pm.h>
+#include <zmk/behavior.h>
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+struct behavior_soft_off_config {
+    uint32_t hold_time_ms;
+};
+
+struct behavior_soft_off_data {
+    uint32_t press_start;
+};
+
+static int behavior_soft_off_init(const struct device *dev) { return 0; };
+
+static int on_keymap_binding_pressed(struct zmk_behavior_binding *binding,
+                                     struct zmk_behavior_binding_event event) {
+    const struct device *dev = device_get_binding(binding->behavior_dev);
+    struct behavior_soft_off_data *data = dev->data;
+
+    data->press_start = k_uptime_get();
+
+    return ZMK_BEHAVIOR_OPAQUE;
+}
+
+static int on_keymap_binding_released(struct zmk_behavior_binding *binding,
+                                      struct zmk_behavior_binding_event event) {
+    const struct device *dev = device_get_binding(binding->behavior_dev);
+    struct behavior_soft_off_data *data = dev->data;
+    const struct behavior_soft_off_config *config = dev->config;
+
+    if (config->hold_time_ms == 0 || (k_uptime_get() - data->press_start) >= config->hold_time_ms) {
+        zmk_pm_soft_off();
+    }
+
+    return ZMK_BEHAVIOR_OPAQUE;
+}
+
+static const struct behavior_driver_api behavior_soft_off_driver_api = {
+    .binding_pressed = on_keymap_binding_pressed,
+    .binding_released = on_keymap_binding_released,
+};
+
+#define BSO_INST(n)                                                                                \
+    static const struct behavior_soft_off_config bso_config_##n = {                                \
+        .hold_time_ms = DT_INST_PROP_OR(n, hold_time_ms, 0),                                       \
+    };                                                                                             \
+    static struct behavior_soft_off_data bso_data_##n = {};                                        \
+    DEVICE_DT_INST_DEFINE(0, behavior_soft_off_init, NULL, &bso_data_##n, &bso_config_##n,         \
+                          APPLICATION, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT,                        \
+                          &behavior_soft_off_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(BSO_INST)