Drivers

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.

participant "platform" as plat participant lib -> plat : platform_init() activate plat == DAI == plat -> plat : dai_disco() : dai_desc_list plat -> lib : dai_install(dai_desc_list) == DMA == plat -> plat : dma_disco() : dma_desc_list plat -> lib : dma_install(dma_desc_list) <-- plat deactivate plat

Figure 21 Device discovery and registration

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.

participant "component" as comp participant lib participant ukernel participant "driver" as drv participant hw -> comp : new() comp -> lib : dai_get(type, ...) activate lib lib -> lib : lookup(dai_desc_list) : dai_desc opt dai_desc->sref == 0 lib -> drv : dai_desc->ops->probe(dai_desc) activate drv drv -> hw : ungate power drv -> ukernel : alloc mem lib <-- drv : Success deactivate drv end opt lib -> lib : dai_desc->sref++ comp <-- lib : dev* deactivate lib

Figure 22 Creating the device on the first use

participant "component" as comp participant lib participant ukernel participant "driver" as drv participant hw -> comp : free() comp -> lib : dai_put(dev*) activate lib opt --dai_desc->sref == 0 lib -> drv : dai_desc->ops->remove(dev) activate drv drv -> ukernel : free mem drv -> hw : gate power lib <-- drv : Success deactivate drv end opt comp <-- lib deactivate lib

Figure 23 Removing the device when no longer in use

API

The drivers are located at: src/drivers