Book Image

Linux Device Drivers Development

By : John Madieu
Book Image

Linux Device Drivers Development

By: John Madieu

Overview of this book

Linux kernel is a complex, portable, modular and widely used piece of software, running on around 80% of servers and embedded systems in more than half of devices throughout the World. Device drivers play a critical role in how well a Linux system performs. As Linux has turned out to be one of the most popular operating systems used, the interest in developing proprietary device drivers is also increasing steadily. This book will initially help you understand the basics of drivers as well as prepare for the long journey through the Linux Kernel. This book then covers drivers development based on various Linux subsystems such as memory management, PWM, RTC, IIO, IRQ management, and so on. The book also offers a practical approach on direct memory access and network device drivers. By the end of this book, you will be comfortable with the concept of device driver development and will be in a position to write any device driver from scratch using the latest kernel version (v4.13 at the time of writing this book).

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Table of Contents (23 chapters)
Preface
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Customer support
Free Chapter
1
Introduction to Kernel Development
Introduction to Kernel Development
Environment setup
Kernel habits
Summary
2
Device Driver Basis
Device Driver Basis
User space and kernel space
Driver skeletons
Errors and message printing
Module parameters
Building your first module
Summary
3
Kernel Facilities and Helper Functions
Kernel Facilities and Helper Functions
Understanding the container_of macro
Linked lists
Kernel sleeping mechanism
Delay and timer management
Kernel locking mechanism
Work deferring mechanism
Kernel interruption mechanism
Threaded IRQs
Invoking user space applications from the kernel
Summary
4
Character Device Drivers
Character Device Drivers
The concept behind major and minor
Introduction to device file operations
Allocating and registering a character device
Writing file operations
Summary
5
Platform Device Drivers
Platform Device Drivers
Platform drivers
Platform devices
Devices, drivers, and bus matching
Summary
6
The Concept of Device Tree
The Concept of Device Tree
Device tree mechanism
Representing and addressing devices
Handling resources
Platform drivers and DT
Summary
7
I2C Client Drivers
I2C Client Drivers
The driver architecture
Accessing the client
I2C and the device tree
Summary
8
SPI Device Drivers
SPI Device Drivers
The driver architecture
Accessing and talking to the client
Putting it all together
SPI user mode driver
Summary
9
Regmap API – A Register Map Abstraction
Regmap API – A Register Map Abstraction
Programming with the regmap API
Summary
10
IIO Framework
IIO Framework
IIO data structures
Triggered buffer support
IIO data access
IIO tools
Summary
11
Kernel Memory Management
Kernel Memory Management
System memory layout - kernel space and user space
Address translation and MMU
Memory allocation mechanism
Work with I/O memory to talk with hardware
Memory (re)mapping
Linux caching system
Device-managed resources – Devres
Summary
12
DMA – Direct Memory Access
DMA – Direct Memory Access
Setting up DMA mappings
The concept of completion
The DMA engine API
Putting it all together – NXP SDMA (i.MX6)
DMA DT binding
Summary
13
The Linux Device Model
The Linux Device Model
LDM data structures
Deep inside LDM
The device model and sysfs
Summary
14
Pin Control and GPIO Subsystem
Pin Control and GPIO Subsystem
Pin control subsystem
The GPIO subsystem
Summary
15
GPIO Controller Drivers – gpio_chip
GPIO Controller Drivers – gpio_chip
Driver architecture and data structures
Pin controller guidelines
Sysfs interface for GPIO controller
GPIO controllers and the DT
Summary
16
Advanced IRQ Management
Advanced IRQ Management
Multiplexing interrupts and interrupt controllers
Advanced peripheral IRQs management
Interrupt request and propagation
Summary
17
Input Devices Drivers
Input Devices Drivers
Input device structures
Allocating and registering an input device
Generating and reporting an input event
User space interface
Putting it all together
Summary
18
RTC Drivers
RTC Drivers
RTC framework data structures
RTCs and user space
Summary
19
PWM Drivers
PWM Drivers
PWM controller driver
PWM consumer interface
Using PWMs with the sysfs interface
Summary
20
Regulator Framework
Regulator Framework
PMIC/producer driver interface
Regulators consumer interface
Regulator binding
Summary
21
Framebuffer Drivers
Framebuffer Drivers
Driver data structures
Device methods
Driver methods
Framebuffer from user space
Summary
22
Network Interface Card Drivers
Network Interface Card Drivers
Driver data structures
The device methods
Driver methods
Summary

Using PWMs with the sysfs interface

The PWM core sysfs root path is /sys/class/pwm/. It is the user space way to manage PWM devices. Each PWM controller/chip added to the system creates a pwmchipN directory entry under the sysfs root path, where N is the base of the PWM chip. The directory contains the following files:

  • npwm: This is a read-only file printing the number of PWM channels that this chip supports
  • Export: This is a write-only file allowing you to export a PWM channel for use with sysfs (this functionality is equivalent to the GPIO sysfs interface)
  • Unexport: Unexports a PWM channel from sysfs (write-only)

The PWM channels are numbered using an index from 0 to pwm<n-1>. These numbers are local to the chip. Each PWM channel exportation creates a pwmX directory in the pwmchipN, which is the same directory as the one containing the export file used. X is the number...

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