Book Image

Linux Device Driver Development - Second Edition

By : John Madieu
Book Image

Linux Device Driver Development - Second Edition

By: John Madieu

Overview of this book

Linux is by far the most-used kernel on embedded systems. Thanks to its subsystems, the Linux kernel supports almost all of the application fields in the industrial world. This updated second edition of Linux Device Driver Development is a comprehensive introduction to the Linux kernel world and the different subsystems that it is made of, and will be useful for embedded developers from any discipline. You'll learn how to configure, tailor, and build the Linux kernel. Filled with real-world examples, the book covers each of the most-used subsystems in the embedded domains such as GPIO, direct memory access, interrupt management, and I2C/SPI device drivers. This book will show you how Linux abstracts each device from a hardware point of view and how a device is bound to its driver(s). You’ll also see how interrupts are propagated in the system as the book covers the interrupt processing mechanisms in-depth and describes every kernel structure and API involved. This new edition also addresses how not to write device drivers using user space libraries for GPIO clients, I2C, and SPI drivers. By the end of this Linux book, you’ll be able to write device drivers for most of the embedded devices out there.
Table of Contents (23 chapters)
1
Section 1 -Linux Kernel Development Basics
6
Section 2 - Linux Kernel Platform Abstraction and Device Drivers
12
Section 3 - Making the Most out of Your Hardware
18
Section 4 - Misc Kernel Subsystems for the Embedded World

Chapter 12: Abstracting Memory Access – Introduction to the Regmap API: a Register Map Abstraction

Before the Regmap API was developed, there was redundant code for the device drivers dealing with SPI, I2C, or memory-mapped devices. Many of these drivers contained some very similar code for accessing hardware device registers.

The following figure shows how SPI, I2C, and memory-mapped related APIs were used standalone before Regmap was introduced:

Figure 12.1 – I2C, SPI, and memory-mapped access before Regmap

The Regmap API was introduced in version v3.1 of the Linux kernel and proposes a solution that factors out and unifies these similar register access codes, saving code and making it much easier to share infrastructure. It is then just a matter of how to initialize and to configure a regmap structure, and process any read/write/modify operations fluently, whether it is SPI, I2C, or memory-mapped.

The following diagram depicts this API...