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

Setting and copying on MMIO memory regions

The kernel also provides helper routines for the memset() and memcpy() operations when using MMIO. Note that you must use the following helpers:

#include linux/io.h

void memset_io(volatile void __iomem *addr, int value, size_t size);

This will set the I/O memory from the start address, addr (an MMIO location), to the value specified by the value parameter for size bytes.

For the purpose of copying memory, two helper routines are available, depending on the direction of the memory transfer:

void memcpy_fromio(void *buffer, const volatile void __iomem *addr, size_t size);
void memcpy_toio(volatile void __iomem *addr, const void *buffer, size_t size);

The first copies memory from the MMIO location addr to the (kernel-space) destination buffer (buffer) for size bytes; the second routine copies memory from the (kernel-space) source buffer (buffer) to the destination MMIO location addr for size bytes. Again...