RiscVPkg: Implement ResetSystem RuntimeService

[JohnAZoidberg]

When executing the reset command in the UEFI shell, the debug message is printed but the VM gets stuck. Not sure whether that's my implementation fault or OpenSBI&QEMU.

To try this PR, the following patch also needs to be applied to edk2-platforms:

--- i/Platform/SiFive/U5SeriesPkg/FreedomU540HiFiveUnleashedBoard/U540.dsc
+++ w/Platform/SiFive/U5SeriesPkg/FreedomU540HiFiveUnleashedBoard/U540.dsc
@@ -427,7 +427,8 @@
   MdeModulePkg/Universal/BdsDxe/BdsDxe.inf
   MdeModulePkg/Universal/ResetSystemRuntimeDxe/ResetSystemRuntimeDxe.inf {
     <LibraryClasses>
-      ResetSystemLib|MdeModulePkg/Library/BaseResetSystemLibNull/BaseResetSystemLibNull.inf
+      ResetSystemLib|RiscVPkg/Library/ResetSystemLib/ResetSystemLib.inf
   }
   EmbeddedPkg/RealTimeClockRuntimeDxe/RealTimeClockRuntimeDxe.inf

[changab]

The same reason, access to MSCRATCH in S-Mode is invalid.
This is what we are going to outline the clear architecture, I will do that.
We should work on those tasks from the bottom to top layer. Otherwise, you may have to revise your code often. I will prioritize it according to the TODO you listed.

[JohnAZoidberg]

Right... that was stupid.
I changed it to make the shutdown ecall.
Now it properly calls into OpenSBI, however that function doesn't do anything: https://github.com/changab/edk2-platforms/blob/master/Platform/SiFive/U5SeriesPkg/FreedomU540HiFiveUnleashedBoard/Library/OpensbiPlatformLib/Platform.c#L182

[JohnAZoidberg]

I think this is good and stable. It only uses the SBI ecall interface.
For other reset types we'll have to think what to do and talk to the RISC-V people.

[changab]

This is the newly generated GUID, right? Just make sure this is not duplicate with others.

[JohnAZoidberg]

Yes, of course ;)
I have the feeling you have been burnt by this mistake in the past? 😆

[changab]

hah, not really. just people sometime forget to use a new one. :)

[changab]

Ok. Please keep this in the pocket. Send out to edk2-mailing list once edk2 RISC-V port gets into master branch.

[changab]

For other reset types we'll have to think what to do and talk to the RISC-V people.

sure. We may have to ask them to create a new extension for shutdown with parameters of reset types, this replaces original Shutdown() API.

[JohnAZoidberg]

Atish has created a draft extension for system reset: avpatel/riscv-sbi-doc@71d1870

We might need to help get this through. He said that it might be easier to get accepted if we present a strong use-case.