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

RMW atomic operations – operating on device registers

Let's quickly go over some basics first: a byte consists of 8 bits, numbered from bit 0, the Least Significant Bit (LSB), to bit 7the Most Significant Bit (MSB). (This is actually formally defined as the BITS_PER_BYTE macro in include/linux/bits.h, along with a few other interesting definitions.)

register is basically a small piece of memory within the peripheral device; typically, its size, the register bit width, is one of 8, 16, or 32 bits. The device registers provide control, status, and other information and are often programmable. This, in fact, is largely what you as a driver author will do – program the device registers appropriately to make the device do something, and query it.

To flesh out this discussion, let's consider a hypothetical device that has two registers: a status register and a control register, each 8 bits wide. (In the real world, every device...