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

Platform devices

A quick but important aside: platform devices are often used to represent the variety of devices on a System on Chip (SoC) within an embedded board. The SoC is typically a very sophisticated chip that integrates various components into its silicon. Besides processing units (CPUs/GPUs), it might house several peripherals too, including Ethernet MAC, USB, multimedia, serial UART, clock, I2C, SPI, flash chip controllers, and so on. A reason we need these components to be enumerated as a platform device is that there is no physical bus within the SoC; thus, the platform bus is used.

Traditionally, the code that was used to instantiate these SoC platform devices was kept in a "board" file (or files) within the kernel source (arch/<arch>/...). Due to it becoming overloaded, it's been moved outside the pure kernel source into a useful hardware description format called the Device Tree (within Device Tree Source (DTS) files that are themselves...