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

The watchdog user space interface

On Linux-based systems, the standard user space interface to the watchdog is the /dev/watchdog file, through which a daemon will notify the kernel watchdog driver that the user space is still alive. The watchdog starts right after the file is opened, and gets pinged by periodically writing into this file.

When the notification occurs, the underlying driver will notify the watchdog device, which will result in resetting its timeout; the watchdog will then wait for yet another timeout duration prior to resetting the system. However, if for any reason the user space does not perform the notification before the timeout is elapsed, the watchdog will reset the system (causing a reboot). This mechanism provides a way to enforce the system availability. Let's start with the basics, learning how to start and stop the watchdog.

Starting and stopping the watchdog

The watchdog is automatically started once you open the /dev/watchdog device file,...