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 Linux media controller framework

Media devices turn out to be very complex, involving several IP blocks of the SoC and thus requiring video stream (re)routing.

Now, let's consider a case where we have a much more sophisticated SoC made of two more on-chip sub-devices – let's say a resizer and an image converter, called baz and biz.

In the previous example in the V4L2 async section, the setup was made up of one bridge device and one sub-device (the fact that it is off-chip does not matter), the camera sensor. This was quite straightforward. Luckily, things worked. But what if now we have to route the stream through the image converter or the image resizer, or even through both IPs? Or, say we have to switch from one to the other (dynamically)?

We could achieve this either via sysfs or ioctls, but this would have the following problems:

  • It would be too ugly (no doubt) and probably buggy.
  • It would be too hard (a lot of work).
  • It would be deeply...