The drivers controls the devices attached to the platform. The following type of devices are typically available:
DMA (Direct Memory Access) devices
DAI (Digital Audio Interface) devices
Registering the Devices¶
The devices are connected to other topology elements when the topology is being created. The infrastructure (lib) needs to know what devices are available and how to connect to their drivers’ APIs. The platform initialization routine is responsible for the device discovery and API registration. The discovery mechanism depends on the platform. It may be either very simple statically compiled list of the devices or a dynamic one based on capability information provided by the underlying HW at run-time.
Probing on Demand¶
Creation of the particular device may result in a significant resource allocation and increased power demand. Therefore the infrastructure does not create (probe) the devices immediately upon startup. A simple reference counting mechanism implemented inside the lib allows to probe the devices on demand and free (remove) them when no longer in use.
The device driver implementation of
remove() API is required to free all
the resources allocated in
probe() and power-gate unused HW blocks.