Linux Device Drivers – Complete Guide for Embedded

Linux Device Drivers

Linux device drivers form the backbone of any Embedded Linux system. Linux device drivers act as the critical interface between hardware devices and the Linux kernel, enabling seamless communication between physical peripherals and user-space applications. Without Linux device drivers, the operating system cannot control or interact with hardware such as keyboards, displays, storage devices, sensors, or network interfaces. In embedded Linux device drivers, hardware-specific complexities are abstracted, providing a standardized interface that ensures safety, stability, and performance. This abstraction allows developers to focus on application logic while relying on Linux hardware support offered by the kernel. Linux follows a modular driver architecture, meaning Linux kernel modules can be dynamically loaded and unloaded at runtime. This modularity is especially important in embedded device drivers, where memory and processing resources are limited. Hence, embedded Linux kernel programming relies heavily on efficient Linux driver development practices.

Linux device drivers enable the Linux kernel to communicate with hardware devices by providing a standardized interface.
They manage character, block, network, and USB devices, handling device initialization, data transfer, and safe interaction between user space and hardware in embedded Linux systems.

Classification of Linux Device Drivers

Linux device drivers are broadly classified based on the type of interface they expose to the kernel and user space.

1. Character Device Driver

A char device driver handles devices that transfer data character by character (byte stream) and do not support random access. Examples:
  • Serial ports (/dev/ttyS*, /dev/console, /dev/ttyUSB*)
  • Keyboards
  • Sensors
  • /dev/console
Character devices are accessed sequentially, making Linux device drivers ideal for stream-based communication. Char device driver implementation is a fundamental part of Linux driver development and embedded device drivers training.

2. Block Devices in Linux

Block devices in Linux manage storage devices that transfer data in fixed-size blocks and support random access. Examples:
  • Hard disks (/dev/sda, /dev/sdb)
  • USB flash drives (/dev/sdX)
  • eMMC and SD cards
  • CD-ROMs
Block drivers are widely used in Linux device drivers for storage management. Commands such as fdisk command in Linux, sfdisk command in Linux, and df command in Linux interact directly with block devices. Register for Embedded Linux Training

3. Network Drivers

Network drivers are Linux device drivers responsible for handling packet-based communication. Examples:
  • Ethernet adapters
  • Wi-Fi adapters
  • USB-to-Ethernet converters
These drivers integrate with the Linux network stack, enabling interfaces like eth0. Network drivers highlight the flexibility of Linux device drivers in embedded Linux device drivers development.

Linux Device Drivers Based on Kernel Subsystems

Apart from traditional classification, Linux device drivers can also be grouped based on kernel subsystems. A single device can belong to multiple subsystems.

Example: USB Devices

A USB port itself is generic, but functionality depends on the connected device:
USB Device Type Linux Representation
USB-to-Ethernet Network interface (eth0)
USB serial adapter Character device (/dev/ttyUSB0)
USB mass storage Block device (/dev/sdX)
This flexibility is achieved through the Linux USB subsystem, a key component of Linux driver development. Download Embedded Systems Brochure

Linux USB Subsystem Overview

All USB-based Linux device drivers rely on the Linux USB subsystem, which provides a layered and standardized architecture.

USB Core in Linux

The USB core provides common infrastructure for all USB drivers in Linux:
  • Device detection and enumeration
  • Addressing and bus management
  • Low-level packet transfer handling
  • Common USB APIs for drivers
The Linux USB subsystem abstracts hardware details, enabling USB driver in Linux development to focus only on device-specific functionality.

Device Detection and probe() Callback

Every USB driver in Linux must implement a probe() callback.

Sequence When a USB Device Is Plugged In

  • USB core detects the device
  • Reads descriptors (VID, PID)
  • Matches driver using ID table
  • Calls the driver’s probe() function

Responsibilities of probe()

  • Allocate private driver data
  • Initialize USB endpoints
  • Setup buffers
  • Register with kernel subsystem:
    • Network → register_netdev()
    • Serial → usb_serial_register_drivers()
    • Storage → SCSI layer
After successful registration, the device appears as:
  • /dev/ttyUSB0
  • /dev/sdX
  • eth0
This process is fundamental to Linux device drivers and embedded Linux kernel programming.

USB Request Blocks (URBs)

URBs enable asynchronous data transfers in Linux USB device drivers. Key Features:
  • Asynchronous operation
  • Callback-driven completion
  • Cancelable transfers
URBs ensure efficient, non-blocking communication in embedded Linux device drivers.

disconnect() Callback – Device Removal

When a USB device is unplugged, the disconnect() callback is invoked. Responsibilities:
  • Stop active transfers
  • Unregister device
  • Free allocated memory
This guarantees system stability and is a critical part of the Linux device drivers lifecycle.

usb_driver Structure

struct usb_driver usb_drv = {
    .name       = "usb_drv",
    .probe      = drv_probe,
    .disconnect = drv_disconnect,
    .id_table   = drv_tbl_id,
};
This structure defines how Linux USB device drivers interact with the kernel.

USB Driver Registration

static int __init usb_drv_init(void)
{
    int ret;

    ret = usb_register(&drv_struct);
    if (ret < 0) {
        pr_err("Failed to register usb_drv\n");
        return ret;
    }
    return 0;
}
usb_register() registers the driver usb_deregister() removes it during module unload This completes the lifecycle of a Linux device driver.

Common Linux Driver & Disk Commands

  • df command in Linux
  • fdisk command in Linux
  • sfdisk command in Linux
  • lsblk
  • dev console
  • dev null
  • Linux device manager utilities
These tools help verify Linux hardware support and device status.

Why Learn Linux Device Drivers at IIES?

At IIES – Indian Institute of Embedded Systems, we offer the best embedded course in Bangalore, covering:
  • Linux device drivers
  • Embedded Linux device drivers
  • Linux kernel modules
  • Linux driver development
  • Embedded Linux kernel programming
  • Real-time projects & industry mentoring
Our curriculum is designed for engineers aiming to master embedded device drivers and kernel-level development. Talk to Embedded Academic Advisor

Frequently Asked Questions

Linux device drivers allow the Linux kernel to communicate with hardware devices.

A char device driver transfers data sequentially as a byte stream.

Block devices in Linux store data in blocks and support random access.

The Linux USB subsystem manages all USB devices using a common kernel framework.

IIES offers the best embedded course in Bangalore, specializing in Linux device drivers and kernel programming.