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

Video device opening and property management

Drivers expose node entries in the /dev/ directory corresponding to the video interfaces they are responsible for. These file nodes correspond to the /dev/videoX special files for capture devices (in our case). The application must open the appropriate file node prior to any interaction with the video device. It uses the open() system call for that, which will return a file descriptor that will be the entry point for any command sent to the device, as in the following example:

static const char *dev_name = "/dev/video0";
fd = open (dev_name, O_RDWR);
if (fd == -1) {
    perror("Failed to open capture device\n");
    return -1;
}

The preceding snippet is an opening in blocking mode. Passing O_NONBLOCK to open() would prevent the application from being blocked if there is no ready buffer while trying to dequeue. Once you're done with the video device, it should be closed...