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 V4L2 async interface and the concept of graph binding

So far, with V4L2 driver development, we have not actually dealt with the probing order. That being said, we considered the synchronous approach, where bridge device drivers register devices for all sub-devices synchronously during their probing. However, this approach cannot be used with intrinsically asynchronous and unordered device registration systems, such as the flattened device tree. To address this, what we currently call the async interface has been introduced.

With this new approach, bridge drivers register lists of sub-device descriptors and notifier callbacks, and sub-device drivers register sub-devices that they are about to probe or have successfully probed. The async core will take care of matching sub-devices against hardware descriptors and calling bridge driver callbacks when matches are found. Another callback is called when the sub-device is unregistered. The async subsystem relies on device declaration...