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

Understanding Syscon and simple-mfd

Syscon stands for system controller. SoCs sometimes have a set of MMIO registers dedicated to miscellaneous features that don't relate to a specific IP. Clearly, there can't be a functional driver for this as these registers are neither representative nor cohesive enough to represent a specific type of device. The syscon driver handles this kind of situation. Syscon permits other nodes to access this register space through the regmap mechanism. It is actually just a set of wrapper APIs for regmap. When you request access to syscon, the regmap is created, if it doesn't exist yet.

The header required for using the syscon API is <linux/mfd/syscon.h>. As this API is based on regmap, you must also include <linux/regmap.h>. The syscon API is implemented in drivers/mfd/syscon.c in the kernel source tree. Its main data structure is struct syscon, though this structure is not to be used directly:

struct syscon {
  ...