Book Image

Mastering Linux Device Driver Development

By : John Madieu
Book Image

Mastering Linux Device Driver Development

By: John Madieu

Overview of this book

Linux is one of the fastest-growing operating systems around the world, and in the last few years, the Linux kernel has evolved significantly to support a wide variety of embedded devices with its improved subsystems and a range of new features. With this book, you’ll find out how you can enhance your skills to write custom device drivers for your Linux operating system. Mastering Linux Device Driver Development provides complete coverage of kernel topics, including video and audio frameworks, that usually go unaddressed. You’ll work with some of the most complex and impactful Linux kernel frameworks, such as PCI, ALSA for SoC, and Video4Linux2, and discover expert tips and best practices along the way. In addition to this, you’ll understand how to make the most of frameworks such as NVMEM and Watchdog. Once you’ve got to grips with Linux kernel helpers, you’ll advance to working with special device types such as Multi-Function Devices (MFD) followed by video and audio device drivers. By the end of this book, you’ll be able to write feature-rich device drivers and integrate them with some of the most complex Linux kernel frameworks, including V4L2 and ALSA for SoC.
Table of Contents (19 chapters)
1
Section 1:Kernel Core Frameworks for Embedded Device Driver Development
6
Section 2: Multimedia and Power Saving in Embedded Linux Systems
13
Section 3: Staying Up to Date with Other Linux Kernel Subsystems

Chapter 4: Storming the Common Clock Framework

From the beginning, embedded systems have always needed clock signals in order to orchestrate their inner workings, either for synchronization or for power management (for example, enabling clocks when the device is in active use or adjusting the clock depending on some criteria, such as the system load). Therefore, Linux has always had a clock framework. There has only ever been programming interface declaration support for software management of the system clock tree, and each platform had to implement this API. Different System on Chips (SoCs) had their own implementation. This was okay for a while, but people soon found that their hardware implementations were quite similar. The code also became bushy and redundant, which meant it was necessary to use platform-dependent APIs to get/set the clock.

This was rather an uncomfortable situation. Then, the common clock framework (CCF) came in, allowing software to manage clocks available...