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

PMIO – performing the actual I/O

Port I/O is pretty simple compared to all the hoopla we saw with MMIO. This is because the processor provides machine instructions to directly perform the work. Of course, just like MMIO, you are expected to politely ask the kernel for permission to access a PIO region (we covered this in the Asking the kernel's permission section). The APIs for doing this are request_region() and release_region() (their parameters are identical to their MMIO counterpart APIs).

So, how can you access and perform I/O (reads and writes) upon the I/O port(s)? Again, the kernel provides API wrappers over the underlying assembly/machine instructions to do so for both reading and writing. Using them, you can perform I/O reads and writes in three possible bit-widths; that is, 8-bit, 16-bit, and 32-bit:

  • PMIO reads: inb(), inw(), and inl()
  • PMIO writes: outb(), outw(), and outl()

Quite intuitively, b implies byte-wide (8 bits), w implies word-wide ...