Re: [RFC] [PATCH 0/2] Proposal to add EFI_MP_SERVICES_PROTOCOL support for AARCH64


Samer El-Haj-Mahmoud
 

Hello Leif,


But it might be good to hear something from ARM whether the use of
this
protocol which "must be produced on any system with more than one
logical processor"
*should* be able to rely on anything being set up for it, or whether we
need an aforementioned helper library.
This statement (from the PI spec) is overly ambitious. I bet that it
does not hold true today on most DXE-based UEFI implementations on
other architectures, not just AARCH64. If we agree, I will file an
ECR to remove this statement from the PI spec.
That feels like a weird response to the submission of a patch set
adding the functionality for AArch64.
Agree this comment is not directly related to the RFC, and should be directed to the UEFI Forum instead, so please ignore my comment.



From AARCH64 SBBR systems point of view:

* The requirements from Arm SBBR point of view are around using
PSCI to online/offline Secondary cores, and leaving them
offlined before ReadyToBoot is signaled.
SBBR is not relevant here. PI covers firmware internals, not OS
boot compatibility.

* PI-based UEFI implementations are not required. And even when
they are implemented, the EFI_MP_SERVICES_PROTOCOL is not
required
So ARM's strategy is to encourage people not to us it *in* PI
implementations, even when it is portably implemented on top of PSCI?
Arm does not have any PI specific requirements on platform firmware, beyond what is in the PI spec itself. Arm's official requirements are only on OS boot interoperability (SBBR).

For the RFC itself, I personally do not have any objection, and welcome the addition of this protocol to AARCH64, as long as it utilizes the PSCI services to achieve the OS boot requirements.

It may be worth getting feedback from Sami since he is the EDK2 maintainer for Arm platforms.



Regards,

Leif

* I agree with the analysis in this thread. EFI_MP
implementations on AARCh64 need to be severely limited in the
general case. Platforms (upstream or downstream) can still
innovate and write their own code to run in these services as
they wish.


Thanks,
--Samer


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