RidgeRun Linux Camera Drivers - What is a driver?
Introduction to Device Drivers
Device drivers serve as a gateway for understanding and modifying the kernel, offering a modular approach that allows them to be built separately and plugged in at runtime. The role of device drivers is to provide a standardized interface for hardware, hiding complexities of the device from the user.
A device driver can also be interpreted as a specialized software component in the Linux kernel that acts as a “black box” to make hardware devices respond to a well-defined internal programming interface, with these characteristics:
- Role: It provides the mechanism to access hardware without enforcing specific policies on how the hardware should be used.
- Modularity: Drivers can be built separately from the kernel and plugged in at runtime, making them easy to write and maintain.
- Flexibility: A good driver offers access to hardware capabilities without adding constraints, allowing different applications to use the hardware in various ways.
A data structure called the device tree (DT) works together with device drivers to manage hardware configuration in operating systems like Linux. The DT provides a structured way to describe hardware, allowing the operating system to understand the hardware layout without hard-coded details. Each device in the DT includes a compatible property, which helps the operating system match the device with the appropriate driver.
The device tree offers a detailed description of the hardware, structured in a format that the kernel can easily interpret. During the boot process, the kernel reads the device tree to initialize the described hardware, loading and matching device drivers to hardware components based on the compatible property. This setup allows the device tree to pass configuration parameters, such as clock frequencies, GPIO mappings, and interrupt lines, to the device drivers. By decoupling hardware description from the kernel code, the device tree enhances flexibility, enabling hardware configuration changes without modifying the kernel source code, simply by updating the device tree itself, this also allows to support various hardware platforms with a single kernel image.

Types of Device Drivers
The Linux drivers can be classified in different ways. one is to classify them by devices, being one of these three types:
- Character devices: These devices are accessed as a stream of bytes, similar to files. Examples include text consoles and serial ports. They typically implement system calls like open, close, read, and write. Camera drivers are categorized as character devices, as they handle image or video data streams.
- Block devices: These devices can host file systems and handle I/O operations in blocks (usually 512 bytes or more). They allow reading and writing any number of bytes at a time.
- Network interfaces: These devices handle data packet transmission and reception, driven by the network subsystem. They manage packets rather than individual connections. Not being a stream-oriented device, a network interface isn’t easily mapped to a node in the file system.
What is a Device Tree?
A device tree is a data structure and language used to describe hardware, decouples the hardware configuration from the board and device driver support in the Linux kernel. These are the key concepts:
- Purpose: It allows the operating system to understand the hardware configuration without hardcoding details, making it easier to support various hardware with a single kernel image.
- Structure: It is a tree or acyclic graph with named nodes and properties, often presented as an XML file.
- Usage: Linux uses device tree data for platform identification, runtime configuration, and device population.
- Benefits: It reduces code duplication and simplifies hardware support by decoupling hardware configuration from the kernel.