Unraveling the S3C2410 Clock Registration: A Deep Dive into Linux Kernel Initialization

Background

The post examines the clock subsystem for the Samsung S3C2410 SoC as implemented in the Linux kernel source file s3c2410-clock.c. It aims to show where the clocks are defined and how they become available to the rest of the kernel.

Clock Definitions

In s3c2410-clock.c each clock is described with fields such as name and parent . For UART devices an additional devname field is added, allowing the driver to distinguish multiple serial ports.

Parent and Derived Clocks

The basic clocks fclk, pclk and hclk appear as parents for many other clocks. Derived clocks such as clk_mpll, clk_f and clk_usb_bus are built on top of these parents, forming a hierarchy that the kernel later uses for frequency scaling and gating.

Registration Process

The clocks are finally registered in the function s3c24xx_register_baseclocks. This function is invoked through a specific call chain during board initialization:

smdk2410_map_io

s3c24xx_init_io

cpu_ids

(details omitted)

s3c2410_init_clocks

s3c24xx_register_baseclocks

The article provides screenshots of each function to illustrate where the registration call occurs.

Conclusion

Understanding the sequence from clock definition to registration helps developers trace how hardware timers become available in the kernel, and provides a roadmap for debugging or extending the clock infrastructure on S3C24xx‑based boards.