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

V4L2 controls infrastructure

Some devices have controls that are settable by the user in order to modify some defined properties. Some of these controls may support a list of predefined values, a default value, an adjustment, and so on. The thing is, different devices may provide different controls with different values. Moreover, while some of these controls are standard, others may be vendor-specific. The main purpose of the control framework is to present controls to the user without assumptions relating to their purpose. In this section, we only address standard controls.

The control framework relies on two main objects, both defined in include/media/v4l2- ctrls.h, like the rest of the data structures and APIs provided by this framework. The first is struct v4l2_ctrl. This structure describes the control properties and keeps track of the control's value. The second and final one is struct v4l2_ctrl_handler, which keeps track of all the controls. Their detailed definitions...