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

Introducing the MFD subsystem and Syscon APIs

Prior to delving into the syscon framework and its APIs, we will cover MFDs. There are peripherals or hardware blocks exposing more than a single functionality by means of subdevices they embed into them and that are handled by separate subsystems in the kernel. That being said, a subdevice is a dedicated entity in a so-called multifunction device, responsible for a specific task, and managed through a reduced set of registers, in the chip's register map. ADP5520 is a typical example of an MFD device, as it contains a backlight, a keypad, LEDs, and GPIO controllers. Each of these is then considered as a subdevice, and as you can see, each of these falls into a different subsystem. The MFD subsystem, defined in include/linux/mfd/core.h and implemented in drivers/mfd/mfd-core.c, has been created to deal with these devices, allowing the following features:

  • Registering the same device with multiple subsystems
  • Multiplexing bus...