Linux kernel driver initialization sequence Adjustment

Article Title: Adjustment of the initialization sequence of Linux kernel drivers. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

We need to use the API provided by another driver (I2C) When making a driver today. We encountered a dependency problem during kernel initialization.

My driver runs before I2C initialization, And the API provided by I2C is still unavailable. I checked a lot of information. Some people on the Internet said that the Starting sequence of all drivers using the module_init macro is uncertain (I have not found any authoritative information ).

All the _ init functions are in the Section. initcall. init also saves a function pointer. during initialization, the kernel will call these _ init function pointers through these function pointers. After the initialization is complete, release the entire init section (including. init. text ,. initcall. init ).

Note that the call sequence of these functions during kernel Initialization is only related to the order of the function pointers here, and 1) the functions themselves are described in. init. the order in the text section is irrelevant. In the 2.4 kernel, the order of these function pointers is also related to the order of links and is uncertain. In the 2.6 kernel, The initcall. init segments are further divided into seven sub-segments:

.initcall1.init .initcall2.init .initcall3.init .initcall4.init .initcall5.init .initcall6.init .initcall7.init

When you need to put the function fn in The. initcall1.init section, you only need to declare

core_initcall(fn);

You can.

The definition methods of other sections are as follows:

core_initcall(fn) --->.initcall1.init postcore_initcall(fn) --->.initcall2.init arch_initcall(fn) --->.initcall3.init subsys_initcall(fn) --->.initcall4.init fs_initcall(fn) --->.initcall5.init device_initcall(fn) --->.initcall6.init late_initcall(fn) --->.initcall7.init

Initcall (fn) compatible with 2.4 is equivalent to device_initcall (fn ). The sequence between sub-sections is determined, that is, the function pointer in. initcall1.init is called first, and the function pointer in. initcall2.init is called, and so on. The order of function pointers in each sub-section is related to the link sequence and is uncertain.

In the kernel, different init functions are placed in different sub-sections, which determines their call sequence. In this way, some init functions must ensure a certain call order. According to the include/linux/init. h file, I tried the following two methods in the driver:

__define_initcall("7", fn);late_initcall(fn);

You can adjust my driver to the final call. In fact, the above two are the same thing:

#define late_initcall(fn) __define_initcall("7", fn)