You're reading from Mastering Linux Device Driver Development Write custom device drivers to support computer peripherals in Linux operating systems

Product type Paperback

Published in Jan 2021

Publisher Packt

ISBN-13 9781789342048

Length 646 pages

Edition 1st Edition

Languages

C++

Tools

Linux

Concepts

Embedded Systems

Author (1):

John Madieu

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Table of Contents (19) Chapters

Preface

1. Section 1:Kernel Core Frameworks for Embedded Device Driver Development

2. Chapter 1: Linux Kernel Concepts for Embedded Developers FREE CHAPTER

3. Chapter 2: Leveraging the Regmap API and Simplifying the Code

4. Chapter 3: Delving into the MFD Subsystem and Syscon API

5. Chapter 4: Storming the Common Clock Framework

6. Section 2: Multimedia and Power Saving in Embedded Linux Systems

7. Chapter 5: ALSA SoC Framework – Leveraging Codec and Platform Class Drivers

8. Chapter 6: ALSA SoC Framework – Delving into the Machine Class Drivers

9. Chapter 7: Demystifying V4L2 and Video Capture Device Drivers

10. Chapter 8: Integrating with V4L2 Async and Media Controller Frameworks

11. Chapter 9:Leveraging the V4L2 API from the User Space

12. Chapter 10: Linux Kernel Power Management

13. Section 3: Staying Up to Date with Other Linux Kernel Subsystems

14. Chapter 11: Writing PCI Device Drivers

15. Chapter 12: Leveraging the NVMEM Framework

16. Chapter 13: Watchdog Device Drivers

17. Chapter 14: Linux Kernel Debugging Tips and Best Practices

18. Other Books You May Enjoy

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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.

After...