Re: [edk2-devel] [PATCH v8 14/37] UefiCpuPkg: Add CpuMmuLib to UefiCpuPkg

["Laszlo Ersek" <lersek@redhat.com>]

Hello Chao,

On 3/4/24 04:39, Chao Li wrote:
> Hi Laszlo,
> 
> OK.
> 
> When I discussed the CpuMmuLib API as a public API with Ray in the early
> days, the API recommended by Ray should be the patch 13 in this series,
> which only contains set/get memory region attribute, but in the first
> version in this series, it contains more API, one is ConfigureMmu API,
> which is included in ARM and RISCV versions. This API provides a
> interface called in PEI or DXE stage, it will configures the MMU and
> enables it, such as creating the page tables, filling the static page
> tables, cofniguring the MMU registers, enbale MMU, etc.
> 
> The paths for ARM and RISCV version APIs:
> 
> ARM: ArmPkg/Include/Library/ArmMmuLib.h
> 
> RISCV: UefiCpuPkg/Include/Library/BaseRiscVMmuLib.h

I have now re-read this subthread in its entirey, and I think I
understand what's up.

What confused me recently was your expression "so should we open
configure API?"

I think what you meant by "opening" was "publicly declaring".

Anyway, here's my recommendation (consistently with what I said earlier
in this thread):

- I think you need a new (lower-level) library class and instance for
exposing ConfigureMemoryManagementUnit().

Please see: <https://edk2.groups.io/g/devel/message/114972> (msgid
<2a91f2f0-df4c-e106-65cd-79be167224f2@redhat.com>).

- I do not recommend trying to unify the new LoongArch library classes
(low level and high level) with "ArmMmuLib.h" or "BaseRiscVMmuLib.h".

Each of "ArmMmuLib.h" and "BaseRiscVMmuLib.h" seems to declare both
low-level and high-level interfaces. For LoongArch, we apparently don't
want that; hence the idea to introduce two library classes for LoongArch
-- that may be considered an improved design.

At the same time, I don't believe that this requires us to unify
"ArmMmuLib.h" and "BaseRiscVMmuLib.h" with the new, LoongArch-motivated
library class design.

Laszlo



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