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

Handling Regmap initialization

As we said earlier, the Regmap API supports SPI, I2C, and memory-mapped register access. Their respective support can be enabled in the kernel thanks to the CONFIG_REGMAP_SPI, CONFIG_REGMAP_I2C, and CONFIG_REGMAP_MMIO kernel configuration options. It can go far beyond that and managing IRQs as well, but this is out of the scope of this book. Depending on the memory access method you need to support in the driver, you will have to call either devm_regmap_init_i2c(), devm_regmap_init_spi(), or devm_ regmap_init_mmio() in the probe function. To write generic drivers, Regmap is the best choice you can make.

The Regmap API is generic and homogenous, and initialization only changes between bus types. Other functions are the same. It is a good practice to always initialize the register map in the probe function, and you must always fill the regmap_config elements prior to initializing the register map using one of the following APIs:

struct regmap *devm_regmap_init_spi...