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 and using top and bottom halves

Much emphasis has been put on the fact that your interrupt handler must complete its work quickly (as explained in the Keep it fast section and elsewhere). Having said that, a practical issue does crop up. Let's consider this scenario: you have allocated IRQn and have written the interrupt handler function to handle this interrupt when it arrives. As you may recall, the function we're talking about here, commonly referred to as thhardirq or ISR (Interrupt Service Routine) or primary handler, is the second parameter to the request_{threaded}_irq() API, the third parameter to the devm_request_irq() API, and the fourth parameter to the devm_request_threaded_irq() API.

As we mentioned previously, there's a quick heuristic to follow: if your hardirq routine's processing consistently exceeds 100 microseconds, then you will need to use alternate...