Uclass

Uclass is a concept used in the U-Boot firmware project to organize devices within its driver model (DM). It provides a higher-level grouping for devices that share a common interface or family, allowing a single class driver to implement behavior applicable to all devices in that class. This reduces duplication and promotes reuse of code across different boards and peripherals.

In the U-Boot DM, there are buses, drivers, and devices, and each device is associated with a uclass. A uclass is identified by an identifier such as UCLASS_I2C, UCLASS_SPI, UCLASS_GPIO, UCLASS_UART, or UCLASS_ETH, among others. A uclass driver implements class-wide operations and may handle tasks that apply to all devices in that class, such as probing, initialization, or power management. The uclass thus serves as a namespace and a container for devices that share a common interface, enabling uniform handling of their common features.

The relationship between buses, devices, and uclasses is hierarchical: a bus hosts devices, and each device belongs to a uclass. This structure allows software components to query or operate on all devices within a class without needing to manage each device individually. It also supports consistent enumeration and initialization of hardware during system startup.

Common examples of uclasses include I2C, SPI, GPIO, UART, MMC/SD, and Ethernet. The exact set of uclasses varies by U-Boot version and board support package. Overall, the uclass framework aims to improve modularity, portability, and maintainability of hardware support across boards and configurations.