| # Devicetree example board driver |
| |
| This is an example devicetree based board driver implementation which can be used as a reference. |
| |
| ## Board driver |
| |
| The board driver initializes the devicetree manager library with the incoming namespace in order to |
| provide connection to |fuchsia_boot::Items| protocol. Once the manager is reads the devicetree using |
| the |fuchsia_boot::Items| protocol, it is used to walk the devicetree and collect node properties. |
| During the devicetree walk, several visitors can be provided to parse and collect node properties. In |
| this example we are using the default visitor set which parses all the standard bindings supported in |
| Fuchsia. See `visitors` folder for more details. Once the walk is completed, the manager is invoked to |
| publish all the devices/nodes. |
| |
| ## Passing the DTB |
| |
| Typically the devicetree blob (DTB) is passed down by the bootloader to the kernel as a | |
| ZBI_TYPE_DEVICETREE| |
| item and made available to the board driver via |fuchsia_boot::Items| protocol. In boards where the |
| bootloader is not yet capable of passing the DTB (typically during board bringup), the kernel ZBI can |
| be appended with the devicetree blob at build time using |zbi_input| and |kernel_zbi_extra_deps|. |
| See `BUILD.gn` for more details. |
| |
| ## Testing |
| |
| The integration test creates a test realm with driver framework, platform bus and the board |
| driver components running in it. The DTB is passed as a test data resource and is provided to the |
| board driver through the fake |fuchsia_boot::Items| protocol implemented in the `board-test-helper` |
| library. The test creates a platform bus device with specified VID, PID to which the board driver will |
| bind to. The board driver would then parse the devicetree and create other child nodes. A typical test |
| would be to enumerate the nodes created. |
