Re: [RFC v2 2/2] hw/riscv: Add server platform reference machine

[Marcin Juszkiewicz]

W dniu 22.03.2024 o 09:50, Heinrich Schuchardt pisze:
>>> I see no mention of device trees in the spec, but I do see ACPI. Do we
>>> really expect a server platform to use DTs?
>>
>> This platform "kind of" follows sbsa-ref where we have very
>> minimalistic device tree sharing information qemu->firmware.
>>
>> libfdt is small, format is known and describes hardware. Firmware is
>> free to make use of it in any way it wants.
>>
>> On sbsa-ref we parse DT in TF-A (base firmware) and provide hardware
>> information to higher level (edk2) via SMC mechanism. Then EDK2
>> creates ACPI tables and provide them to the Operating System.

> We should ensure that only either an ACPI table or a device-tree
> description is passed to the OS and not both, e.g. when using
>
>      qemu-system-riscv64 -kernel vmlinux -M sbsa-ref
>
> But that requirement is not machine specific.

I would not call "qemu-system-* -M machinename -k kernel_image" a proper 
way to boot for several systems emulated by QEMU.

DeviceTree is in rvsp-ref and sbsa-ref because it is easy to process in 
limited space 1st stage of firmware has.

And if we knew how people will mention 'sbsa-ref uses DT' we would use 
something else instead. But that would require adding more code into 
existing firmware projects (libfdt is usually already there).

I did not looked at DT generated for rvsp-ref. I know that sbsa-ref one 
is too minimalistic for kernel use as we added only those fields/nodes 
we need to provide data for firmware.