RT-Thread RTOS
An open source embedded real-time operating system
Input subsystem

Device-tree binding and DM registration: Input device model (DM).

Topic Page
Userspace API Input userspace API (UAPI)
Touch class bridge Input touch bridge
Power / restart keys Input power keys

Input subsystem (API)

Header: drivers/input.h. Typical stack: low-level driver → **rt_input_event / reporters** → handlers (GUI, shell) or **/dev/inputN** (Input userspace API (UAPI)).

Path API
In-kernel listener **rt_input_add_handler**
POSIX process (Smart) **open / read / ioctl / poll on /dev/inputN** — Input userspace API (UAPI)
Legacy touch GUI **struct rt_touch_device** — Input touch bridge

When to use the input core

Use **rt_input_*** when… Consider raw **rt_device** read when…
You want Linux-like EV_KEY / EV_REL / EV_ABS / multitouch slot semantics and multiple listeners. You have a single proprietary app talking to a vendor IOCTL-only touch stack.
You need polling (**rt_input_setup_polling**) for GPIO keys without IRQ storms. GPIO IRQ latency is fine and you do not need unified event routing.

Event contract

  1. **rt_input_set_capability** before **rt_input_device_register** so users know which **type/code** pairs are valid.
  2. For each hardware change, call **rt_input_report_*** then **rt_input_sync** to close the frame (**SYN_REPORT**). Missing **sync** merges events poorly for consumers.
  3. **rt_input_trigger** routes through optional **idev->trigger**—use when you wrap another input device; otherwise **rt_input_event** is enough.

Callback / context rules

  • **rt_input_add_handler → callback**: invoked from **rt_input_event** path—assume thread or workqueue unless your driver documents IRQ delivery; keep **callback short**.
  • **poller->poll**: runs on timer tick—**must not block** or take mutexes that can deadlock with the same thread calling **rt_input_sync**.
  • Touch helpers: **rt_input_setup_touch** / **rt_input_report_touch_*** require **RT_INPUT_TOUCHSCREEN** — Input touch bridge.

Registration lifecycle

  • **rt_input_device_register**: registers underlying **rt_device**; failures leave partially init state—clean up partial setup in error paths.
  • **rt_input_remove_config**: tears down polling/touch dynamic config before unregister if you toggled features at runtime.

Pitfalls

  • ABS without rt_input_set_absinfo: consumers cannot clamp—set min/max/resolution for axes you report.
  • Key autorepeat: not automatic unless a layer implements it—do not assume Linux repeat behavior.
  • Re-entrancy: posting events from inside a handler for the same device can recurse—prefer queueing.

See also