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

Introduction to regmap and its data structures – I2C, SPI, and MMIO

Regmap is an abstraction register access mechanism provided by the Linux kernel that mainly targets SPI, I2C, and memory-mapped registers.

APIs in this framework are bus agnostic and handle the underlying configuration under the hood. That being said, the main data structure in this framework is struct regmap_config, defined in include/linux/regmap.h in the kernel source tree as follows:

struct regmap_config {
   const char *name;
   int reg_bits;
   int reg_stride;
   int pad_bits;
   int val_bits;
   bool (*writeable_reg)(struct device *dev, unsigned int reg);
   bool (*readable_reg)(struct device *dev, unsigned int reg);
   bool (*volatile_reg)(struct device *dev, unsigned int reg);
   bool (*precious_reg)(struct device *dev, unsigned int reg);
   int...