Initlevel

Drivers may depend on other drivers being initialized first, or require the use of System services. Using SYS_INIT or DEVICE_DEFINE and related macros in drivers allows the user to specify the stage of the boot sequence at which the init function will be executed. Any driver will specify one of five initialization levels:

EARLY:

Used very early in the boot process, no dependencies with system service. Can depend on previous component initialization (ex: debug console).

ARCH:

Used for devices that have no dependencies but needed for core initialization (SAU, MPU…)

PRE_CORE:

Used for devices that have no dependencies, such as those that rely on hardware present and needed for system (ex: clock, reset…)

CORE:

Used for devices that need to register a core service and based only on PRE_CORE dependencies.

POST_CORE:

Used for devices that require system services during configuration. At this level the Interrupts are enabled.

REST:

Used for devices that can use all system services and do not provide a core feature.

Within each initialization level you may specify a priority level, relative to other devices in the same initialization level. The priority level is specified as an integer value in the range 0 to 99; lower values indicate earlier initialization.

Note

If device initialization fails, the device is marked as initialized dev->state->initialized = true and the error code is stored in dev->state->init_res.

At the end of init stages, there is no specific strategy: panic, defer (linux)…

device_is_ready function returns true if the device is initialized and no error.

Note

The linker script must include devices.ld, a section is created and stores objects list sorted by level and priority.