Re: [edk2-devel] [PATCH v2 0/3] New RISC-V Patches - Why in edk2-platforms

["Daniel Schaefer" <daniel.schaefer@hpe.com>]

On 5/20/20 1:43 PM, Leif Lindholm wrote:
> On Fri, May 15, 2020 at 15:39:34 +0200, Daniel Schaefer wrote:
>> Previously we had two packages just for RISC-V on our edk2 branch:
>>    RiscVPkg and RiscVPlatformPkg
>> They are now under
>>    Platform/RISC-V/PlatformPkg and Silicon/RISC-V/ProcessorPkg
>> in edk2-platforms.
> 
> Understood. I took my eye off the ball there for a while, but I'm a
> bit confused as to why RiscVPkg isn't going into EDK2. That is very
> counterintuitive. And clearly it will need revisiting if we are to add
> first-class CI checks like those we do with OvmfPkg/ArmVirtPkg.

Yes, I understand your concern. Personally I'd like it also to be in 
EDK2 straight away, however Mike, Bret and Sean have raised valid concerns:

1. RISC-V is very new and potentially unstable - it's quicker to make 
changes in edk2-platforms.

2. If we define new interfaces and libraries in edk2, we can't remove 
them easily because it would be a backwards-incompatible change. 
edk2-platforms isn't quite as strict.

3. Long-term, I think many agree, we should aim to move much of the 
RISC-V code into UefiCpuPkg and OvmfPkg. Mike mentioned that would need 
coordination with ARM maintainers because it might make sense to move 
their code there as well.

Maybe Mike, Bret or Sean would like to provide some more comments?

> I *did* have some outstanding comments specifically with regards to
> large amounts of code duplication between the SMBIOS implementation of
> some closely related RISC-V platforms. That now needs to be revisited.

The SMBIOS code hasn't changed. It has moved to
   Silicon/SiFive/{E51,U54,U54MCCoreplex}/Library/PeiCoreInfoHobLib
You're referring to this library, right?

They build the SMBIOS entries for a particular processor. Yes, the 
values do have a lot of overlap but these files are like configuration 
files. They don't do much, they only set the values of the properties.

Currently it is not possible to let the UEFI firmware get this 
information from the hardware at runtime, especially now, since we're 
running in S-Mode.
To allow that, we created a RISC-V working group to be able to retrieve 
all of this information dynamically from the processor (among other 
goals). Then the vendor will not have to modify these files and hardcode 
the values anymore. Which enables us to create a single library for all 
processors.
See: https://github.com/riscv/configuration-structure

I hope I described everything properly, please correct me otherwise, Abner.

> 
>> In the previous version of this patchseries I forgot to attach the biggest new
>> commit, which adds RiscVEdk2SbiLib. It wraps the ecall interface for calling
>> SBI in a C API and lets PEI and DXE call SBI interfaces. Because we need more
>> M-Mode capabilities in PEI and DXE than SBI gives us, we register another SBI
>> extension, that gives us access to the mscratch register.
> 
> Without looking at it yet, it sounds like that may resolve the only
> remaining major issue I had with RiscVPkg.
> 
>> I hope now it makes more sense.
> 
> It is more clear, as per above I am not sure it makes more sense :)
> Thanks!

Your concerns are very valid, however due to the mentioned trade-offs it 
might not make sense to address them.

- Daniel