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

All in one with the devm_ioremap_resource() API

As a driver author, you should become aware of and employ this useful routine: the devm_ioremap_resource() managed API performs the job of (validity) checking the requested I/O memory region, requesting it from the kernel (internally via the devm_request_mem_region() API), and remapping it (internally via devm_ioremap())! This makes it a useful wrapper for driver authors like you, and its usage is pretty common (in the 5.4.0 kernel code base, it's employed over 1,400 times). Its signature is as follows:

void __iomem *devm_ioremap_resource(struct device *dev, const struct resource *res);

Here's a usage example from drivers/char/hw_random/bcm2835-rng.c:

static int bcm2835_rng_probe(struct platform_device *pdev)
struct resource *r;
r = platform_get_resource(pdev, IORESOURCE_MEM, 0);

/* map peripheral */
priv->base = devm_ioremap_resource(dev, r);
if (IS_ERR(priv->base))