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Mastering Linux Device Driver Development

Mastering Linux Device Driver Development

By : John Madieu
4.8 (4)
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Mastering Linux Device Driver Development

Mastering Linux Device Driver Development

4.8 (4)
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)
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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

Buffer management

You should consider that in V4L2, two buffer queues are maintained: one for the driver (referred to as the INPUT queue) and one for the user (referred to as the OUTPUT queue). Buffers are queued into the driver's queue by the user space application in order to be filled with data (the application uses the VIDIOC_QBUF ioctl for this). Buffers are filled by the driver in the order they have been enqueued. Once filled, each buffer is moved off the INPUT queue and put into the OUTPUT queue, which is the user queue.

Whenever the user application calls VIDIOC_DQBUF in order to dequeue a buffer, this buffer is looked for in the OUTPUT queue. If it's in there, the buffer will be dequeued and pushed to the user application; otherwise, the application will wait until a filled buffer is there. After the user finishes using the buffer, it must call VIDIOC_QBUF on this buffer in order to enqueue it back in the INPUT queue so that it can be filled again.

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