From: "Andrew Fish" <afish@apple.com>
To: "devel@edk2.groups.io" <devel@edk2.groups.io>
Subject: gUefiCpuPkgTokenSpaceGuid.PcdCpuApTargetCstate definition confusion?
Date: Sun, 11 Aug 2019 16:57:49 -0700 [thread overview]
Message-ID: <E65FE425-2723-42E2-9BA6-008ADA416864@apple.com> (raw)
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I was tracking down a Platform C state bug and I noticed the platform code was using this definition [1] for PcdCpuApTargetCstate and wrote that actual value used for Mwait. But the MpInitLIb seems to assume that PcdCpuApTargetCstate is eax[7:4] and it shifts the data left. This ends up with the value being 0 which means C1 for all calculated values.
So my question is which definition is correct? As far as I can tell eax[3:0] are sub C states and thus being able to pass that value would be useful?
There is other code in the MpLib [3] that is also doing the shift so it seems intestinal. But given the PCD definition I can see how the platform code set the wrong value.
[1] PCD Definition
https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/UefiCpuPkg.dec <https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/UefiCpuPkg.dec>
## Specifies the AP target C-state for Mwait during POST phase.
# The default value 0 means C1 state.
# The value is defined as below.<BR><BR>
# @Prompt The specified AP target C-state for Mwait.
gUefiCpuPkgTokenSpaceGuid.PcdCpuApTargetCstate|0|UINT8|0x00000007
[2] UefiCpuPkg code
https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm <https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm>
MwaitLoop:
cli
mov eax, esp ; Set Monitor Address
xor ecx, ecx ; ecx = 0
xor edx, edx ; edx = 0
monitor
mov eax, ebx ; Mwait Cx, Target C-State per eax[7:4]
shl eax, 4
mwait
jmp MwaitLoop
https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c <https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c>
AsmRelocateApLoopFunc (
MwaitSupport,
CpuMpData->ApTargetCState,
CpuMpData->PmCodeSegment,
mReservedTopOfApStack - ProcessorNumber * AP_SAFE_STACK_SIZE,
(UINTN) &mNumberToFinish
);
[3] ApTargetCState shifting
https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/MpLib.c <https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/MpLib.c>
//
// Check AP start-up signal again.
// If AP start-up signal is not set, place AP into
// the specified C-state
//
AsmMwait (CpuMpData->ApTargetCState << 4, 0);
Thanks,
Andrew Fish
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