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)
1
Section 1: Character Device Driver Basics
3
User-Kernel Communication Pathways
5
Handling Hardware Interrupts
6
Working with Kernel Timers, Threads, and Workqueues
7
Section 2: Delving Deeper

The newer breed  the devm_* managed APIs

Now that you understand how to use the request_mem_region() and the just-seen ioremap*() APIs, guess what? The reality is that both these APIs are now considered deprecated; as a modern driver author, you're expected to use the better resource-managed devm_* APIs. (We covered the older ones for a few reasons, including the fact that many older drivers still very much use them, for understanding the basics of using the ioremap() resource management APIs, and for completeness.)

First, let's check out the new resource-managed ioremap, known as devm_ioremap(), in lib/devres.c:

/** 
* devm_ioremap - Managed ioremap()
* @dev: Generic device to remap IO address for
* @offset: Resource address to map
* @size: Size of map
*
* Managed ioremap(). Map is automatically unmapped on driver detach.
*/
void __iomem *devm_ioremap(struct device *dev, resource_size_t offset,
resource_size_t size)

Just as...