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 2: Leveraging the Regmap API and Simplifying the Code

This chapter introduces the Linux kernel register mapping abstraction layer and shows how to simplify and delegate I/O operations to the regmap subsystem. Dealing with devices, whether they are built-in in the SoC (memory mapped I/O, also known as MMIO) or seated on I2C/SPI buses, consists of accessing (reading/modifying/updating) registers. Regmap became necessary because a lot of device drivers open-coded their register access routines. Regmap stands for Register Map. It was primarily developed for ALSA SoC (ASoC) in order to get rid of redundant open-coded SPI/I2C register access routines in codec drivers. At its origin, regmap provided a set of APIs for reading/writing non-memory-map I/O (for example, I2C and SPI read/write). Since then, MMIO regmap has been upgraded so that we can use regmap to access MMIO.

Nowadays, this framework abstracts I2C, SPI, and MMIO register access, and not only handles locking when necessary...