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Device Drivers

How hardware becomes accessible to userspace

Overview

Device drivers bridge hardware and the rest of the kernel. The Linux driver model organizes this with:

  • Devices (struct device) — represent hardware or logical devices
  • Buses (struct bus_type) — communication channel (PCI, USB, I2C, platform)
  • Drivers (struct device_driver) — code that handles a specific device
  • Classes (struct class) — groups of devices with similar behavior (e.g., "input", "net")
sysfs (/sys/bus/pci/devices/0000:00:1f.2)
         │
         ▼
struct device ←────── struct pci_dev (bus-specific extension)
         │
    bus_type.match()
         │
         ▼
struct device_driver ←── struct pci_driver (driver-specific extension)
         │
    driver.probe()
         │
         ▼
    Hardware

Pages in this section

Page What it covers
Linux Device Model struct device, bus, driver, kobject, sysfs
Platform Drivers Platform bus, probe/remove, devm_, device tree
Character and Misc Devices cdev, file_operations, ioctl, mmap from driver side

Quick reference

# List all devices and their drivers
ls /sys/bus/pci/devices/
ls /sys/bus/platform/devices/

# See driver for a device
cat /sys/bus/pci/devices/0000:00:1f.2/driver/module/name

# Load a kernel module
modprobe e1000e
lsmod | grep e1000

# Bind/unbind a driver manually
echo "0000:00:1f.2" > /sys/bus/pci/drivers/ahci/unbind
echo "0000:00:1f.2" > /sys/bus/pci/drivers/ahci/bind

# Character device major/minor
ls -la /dev/null /dev/random
# crw-rw-rw- 1 root root 1, 3 ... /dev/null  ← major=1, minor=3