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Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

You're reading from   Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization Create user-kernel interfaces, work with peripheral I/O, and handle hardware interrupts

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Product type Paperback
Published in Mar 2021
Publisher Packt
ISBN-13 9781801079518
Length 452 pages
Edition 1st Edition
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Author (1):
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Kaiwan N. Billimoria Kaiwan N. Billimoria
Author Profile Icon Kaiwan N. Billimoria
Kaiwan N. Billimoria
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Table of Contents (11) Chapters Close

Preface 1. Section 1: Character Device Driver Basics
2. Writing a Simple misc Character Device Driver FREE CHAPTER 3. User-Kernel Communication Pathways 4. Working with Hardware I/O Memory 5. Handling Hardware Interrupts 6. Working with Kernel Timers, Threads, and Workqueues 7. Section 2: Delving Deeper
8. Kernel Synchronization - Part 1 9. Kernel Synchronization - Part 2 10. Other Books You May Enjoy

Looking up the port(s) via /proc/ioports

The kernel provides a viewport into the port address space via the /proc/ioports pseudo-file. Let's check it out on our x86_64 guest VM (again, we're only showing part of the output):

$ sudo cat /proc/ioports 
[sudo] password for llkd:
0000-0cf7 : PCI Bus 0000:00
0000-001f : dma1
0020-0021 : pic1
0040-0043 : timer0
0050-0053 : timer1
0060-0060 : keyboard
0064-0064 : keyboard
0070-0071 : rtc_cmos
0070-0071 : rtc0
[...]
d270-d27f : 0000:00:0d.0
d270-d27f : ahci
$

We've highlighted the keyboard ports in bold. Notice how the port numbers match what the i8042 driver code we saw previously specifies. Interestingly, running the same command on the Raspberry Pi yields nothing; this is because no driver or subsystem is using any I/O ports. Analogous with MMIO, an entry in /proc/ioports is generated when the request_region() API runs, and, conversely, is removed when the corresponding release_region...

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