Book Image

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

By : Kaiwan N Billimoria
Book Image

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

By: Kaiwan N Billimoria

Overview of this book

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization is an ideal companion guide to the Linux Kernel Programming book. This book provides a comprehensive introduction for those new to Linux device driver development and will have you up and running with writing misc class character device driver code (on the 5.4 LTS Linux kernel) in next to no time. You'll begin by learning how to write a simple and complete misc class character driver before interfacing your driver with user-mode processes via procfs, sysfs, debugfs, netlink sockets, and ioctl. You'll then find out how to work with hardware I/O memory. The book covers working with hardware interrupts in depth and helps you understand interrupt request (IRQ) allocation, threaded IRQ handlers, tasklets, and softirqs. You'll also explore the practical usage of useful kernel mechanisms, setting up delays, timers, kernel threads, and workqueues. Finally, you'll discover how to deal with the complexity of kernel synchronization with locking technologies (mutexes, spinlocks, and atomic/refcount operators), including more advanced topics such as cache effects, a primer on lock-free techniques, deadlock avoidance (with lockdep), and kernel lock debugging techniques. By the end of this Linux kernel book, you'll have learned the fundamentals of writing Linux character device driver code for real-world projects and products.
Table of Contents (11 chapters)
Section 1: Character Device Driver Basics
User-Kernel Communication Pathways
Handling Hardware Interrupts
Working with Kernel Timers, Threads, and Workqueues
Section 2: Delving Deeper

Understanding level- and edge-triggered interrupts a brief note

When a peripheral asserts an interrupt, the interrupt controller is triggered to latch this event. The electrical characteristics that it uses to trigger the hardware interrupt in the CPU fall into two broad categories:

  • Level-triggered: The interrupt is triggered when the level changes (from inactive to active or asserted); until it's deasserted, the line remains in the asserted state. This happens even after your handler returns; if the line is still asserted, you will get the interrupt again.
  • Edge-triggered: The interrupt triggers only once when the level changes from inactive to active.

Additionally, the interrupt could be high or low triggered, on the rising or falling (clock) edge. The kernel allows this to be configured and specified via additional flags such as IRQF_TRIGGER_NONE, IRQF_TRIGGER_RISING, IRQF_TRIGGER_FALLING, IRQF_TRIGGER_HIGH, IRQF_TRIGGER_LOW, and so on. These low...