Re: [edk2-devel] [PATCH v2 23/30] OvmfPkg/LoongArchVirt: Add PeiServiceTablePointerLib

["Chao Li" <lichao@loongson.cn>]

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Hi Laszlo,

I see, I will look into this PI SPEC and try to implement it in MdePkg 
first and then to update the SPEC.


Thanks,
Chao
On 2023/11/13 19:02, Laszlo Ersek wrote:
> On 11/10/23 07:44, Chao Li wrote:
>> Hi Laszlo,
>>
>> This is a good question, same as the previous email, some ARCH don't
>> require running code on memory during PEI phase or other reason can not
>> used the MdePkg version, so this pointer will be saved by some register,
>> I saw the ArmPkg version also uses a register to save this pointer.
>>
>> If I move ArmPkg version PeiServiceTablePointer to MdePkg and the method
>> of getting and saving the pointer use a new library which related
>> architecture, other word, the API of PeiServiceTablePointer has not
>> changed, adding a new library that PeiServiceTablePointer depends on,
>> the real saving and reading method completed in the new library. Do you
>> think this way is better?
> Right. I think you need a loongarch-specific library instance of
> PeiServicesTablePointerLib under MdePkg. Presumably, if / when you
> enable edk2 on *physical* loongarch platforms, you're going to need the
> same library instance. And therefore it should not be under OvmfPkg, but
> MdePkg.
>
> In fact, now that I'm reading the comments in
> "MdePkg/Library/PeiServicesTablePointerLibIdt/PeiServicesTablePointer.c",
> it seems that the architecture bindings in the Platform Init
> specification actually document how the PEI services table pointer is
> supposed to be stored before system memory becomes available (IIUC).
>
> The latest version of the PI spec that I have is 1.8.
>
> In Volume I, there is a section titled "I-9.4 PEI Services Table
> Retrieval". It considers the following architectures: X86, x64, Itanium,
> ARM, AArch64, RISC-V.
>
> I think that in the longer term, you should file a PIWG Mantis ticket
> for extending this section, with an Engineering Change Request where you
> describe how this mechanism should work on loongarch.
>
> And then the implementation certainly belongs to MdePkg.
>
> (Note that I'm *not* saying you should first update the specification
> and then implement it in edk2 -- that's not my point. My point is that
> *eventually*, this mechanism will become a part of the public loongarch
> bindings, and therefore you can already start introducing it under
> MdePkg, in my opinion anyway.)
>
> Note that "prior art" is inconsistent here, regarding edk2 locations,
> because, as you say, the arm/aarch64 implementation lives under ArmPkg
> -- but it's quite unlikely IMO that a LoongArchPkg top-level directory
> would be introduced. In the longer term, we might want to consolidate
> all PeiServicesTablePointerLib instances under MdePkg.
>
>
> Then your question is, IIUC, whether to reuse any portion of the ArmPkg
> implementation. I don't think that's necessary; the library is so small,
> there is effectively *nothing generic* in it. Put differently, all of it
> is architecture specific. Thus I think you can just add a totally
> self-contained loongarch instance.
>
> Laszlo
>
>
>
> 
>


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