FdtBusDxe: consider a setprop like interface.

[andreiw]

Use case is ArmVirtPkg/Library/ArmVirtPL031FdtClientLib/ArmVirtPL031FdtClientLib.c.

E.g. a driver binding to the RTC device need to disable the RTC device so that the OS always goes through UEFI RT.

Depends on #8

[andreiw]

Consider https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL too, in the sense that a different client-requested tree may be used for fixups. EFI_DT_FIXUP_PROTOCOL can be implemented by FdtBusDxe, the real question is how to push the patching down into DT device drivers (another CB?)

[andreiw]

RiscVVirt/Library/VirtNorFlashPlatformLib/VirtNorFlashDeviceTreeLib.c is another good example where this would be useful functionaly.

[andreiw]

One major problem is that setprop (FdtClient->SetNodeProperty as called by VirtNorFlashPlatformLib) is destructive to the devicetree. Node offsets get changed, so every DtDevice becomes invalid.

So if an interface is added, it should not modify the in-use Devicetree. The updates could be pended, and stored as "command" /path/to/node" "property" "value". This would work well with something like EFI_DT_FIXUP_PROTOCOL, too, in that they could be applied to arbitrary (but similar enough) trees.

The DT should be installed in the ConfigurationTable at EFI_EVENT_GROUP_AFTER_READY_TO_BOOT. That is, a copy of the active DT with the updates applied.

[andreiw]

OnPlatformHasDeviceTree needs to register a EFI_EVENT_GROUP_AFTER_READY_TO_BOOT event. Also OnPlatformHasDeviceTree should be renamed to "OnDevicetreeExposedToOs" or similar.