RT-Thread RTOS
An open source embedded real-time operating system
Bus and driver binding (core)

Device model: bus and driver

RT-Thread DM binds drivers to devices through **struct rt_bus**: each bus keeps linked lists of devices and drivers, runs **match**, then **probe** / **remove** / **shutdown**. Most SoC drivers use the built-in **platform** bus; other stacks (e.g. RPMsg) register their own bus type on the same core.

Headers: components/drivers/include/drivers/core/bus.h, driver.h. Core: components/drivers/core/bus.c. Reference bus: components/drivers/core/platform.c.

Device-side helpers (rt_dm_dev_iomap, properties, IRQ): Device model helpers (dm.h).

Kconfig

Option Role
**RT_USING_DM** Enables **bus.c**, **driver.c**, platform bus, and DM helpers
**RT_USING_DEV_BUS** Optional **rt_device_bus_create** — bus as **RT_Device_Class_Bus** device
**RT_USING_OFW** Platform **match** uses **compatible**; devices carry **dev->ofw_node**
**RT_USING_PINCTRL** Platform **probe** applies **pinctrl-*** before driver **probe**
**RT_USING_CLK** Platform **probe** runs **rt_ofw_clk_set_defaults**

Architecture

rt_bus_register(bus)
|
v
struct rt_bus (platform, rpmsg, ...)
dev_list --> rt_device
drv_list --> rt_driver
match / probe / remove / shutdown

Binding (bus.c): **rt_bus_add_device** walks **drv_list**; **rt_bus_add_driver** walks **dev_list**. **match** must succeed before **dev->drv** is set and **bus->probe(dev)** runs. Failed probe clears **dev->drv**.

Object Role
**struct rt_bus** Bus type and lifecycle hooks
**struct rt_driver** Driver on a bus; **ref_count** = bound devices
**struct rt_platform_device** Platform device embedding **rt_device**

<tt>struct rt_bus</tt> callbacks

Callback Contract
**match** Pure — no HW access; return **RT_TRUE** to bind
**probe** Bus-level setup (platform: pinctrl, clocks, power domain) then driver **probe**
**remove** Teardown; platform calls **pdrv->remove** and **rt_platform_ofw_free**
**shutdown** Invoked from **rt_bus_shutdown()** on system off

Bus and driver API

API Role
**rt_bus_register** Register bus on global **bus_nodes**
**rt_bus_add_device / rt_bus_add_driver** Add node and run matching
**rt_bus_remove_device / rt_bus_remove_driver** Remove; driver busy if **ref_count > 0**
**rt_bus_for_each_dev / rt_bus_for_each_drv** Iterate under spinlock
**rt_bus_find_by_name** Find **"platform"** etc.
**rt_bus_reload_driver_device** Move device to another bus
**rt_bus_shutdown** Shutdown all devices on all buses
**rt_driver_register / unregister** Driver attach/detach

<tt>RT_DRIVER_EXPORT</tt> / platform

#define RT_DRIVER_EXPORT(driver, bus_name, mode) /* INIT_DEVICE_EXPORT */
#define RT_PLATFORM_DRIVER_EXPORT(driver) \
RT_DRIVER_EXPORT(driver, platform, BUILIN)

Example:

static const struct rt_ofw_node_id my_ids[] = {
{ .compatible = "vendor,my-ip" },
{ /* sentinel */ },
};
static struct rt_platform_driver my_drv = {
.name = "my-ip",
.ids = my_ids,
.probe = my_probe,
.remove = my_remove,
};
RT_PLATFORM_DRIVER_EXPORT(my_drv);

Platform bus

**INIT_CORE_EXPORT(platform_bus_init)** registers **name = "platform"**.

<tt>platform_match</tt>

  1. **rt_ofw_node_match(np, pdrv->ids)** when **dev->ofw_node** is set.
  2. Else compare **pdev->name** and **pdrv->name**.

<tt>platform_probe</tt> (before <tt>pdrv->probe</tt>)

  1. Pinctrl default / index 0 — Pin control (pinctrl)
  2. **rt_ofw_clk_set_defaults** — Clock framework (CLK)
  3. **rt_dm_power_domain_attach(dev, RT_TRUE)** — **-RT_EEMPTY** OK — Power domain
  4. **pdrv->probe(pdev)** — map MMIO, clocks, register **rt_device**
OFW API Role
**rt_platform_ofw_request** Instantiate from DT node
**rt_platform_ofw_device_probe_child** Probe children
**rt_platform_ofw_free** Free OFW state on remove

See Platform bus, Open Firmware (OFW).

Custom <tt>rt_bus</tt>

New bus when… Use platform when…
Non-OFW enumeration (RPMsg, internal stack bus) **/soc** MMIO + **compatible**

Implement **match/probe/remove**, **rt_bus_register** at init, then **rt_bus_add_driver** / **rt_bus_add_device**.

SDIO vs core

MMC-specific DM: SDIO device model. This page covers **rt_bus / rt_driver** only.

Power and probe order

Topic Document
System shutdown System power off and reboot (core)
Power domains Power domain
Regulators Regulator

Typical order: regulator → power domain → clock/reset → rt_dm_dev_iomap.

Engineer checklist

  1. Export driver with **RT_PLATFORM_DRIVER_EXPORT** (or subsystem **RT_DRIVER_EXPORT**).
  2. Request device via **rt_platform_ofw_request** or manual register.
  3. In **probe**: resources → HW → register functional device; unwind on error.
  4. In **remove**: reverse order; disable IRQ before free.

Pitfalls

  • **match with side effects** breaks re-probe.
  • Double rt_bus_add_device without remove.
  • **rt_driver_unregister while devices bound** — **-RT_EBUSY**.
  • Link order is not probe order — defer on missing phandles.

See also