From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: Re: [edk2-devel] [edk2-platforms][PATCH v1 1/1] IntelSiliconPkg: Add BaseSmmAccessLibNull
To: Ni, Ray <ray.ni@intel.com>,devel@edk2.groups.io
From: "Michael Kubacki" <mikuback@linux.microsoft.com>
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Date: Thu, 12 Aug 2021 19:16:04 -0700
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Sure.

Scenario #1:

MinPlatformPkg/PlatformInit/PlatformInitPei/PlatformInitPreMem.inf and MinP=
latormPkg/PlatformInit/PlatformInitPei/PlatformInitPostMem.inf both link ag=
ainst an instance of BoardInitLib.

Many boards link against a single BoardInitLib instance. See example - http=
s://github.com/tianocore/edk2-platforms/blob/cd4e6b716c7d1bcde94035e7dce14b=
53a553e103/Platform/Intel/KabylakeOpenBoardPkg/KabylakeRvp3/OpenBoardPkg.ds=
c#L203

That BoardInitLib instance may link against SmmAccessLib. PlatformInitPreMe=
m may wish to library class override the SmmAccessLib to the NULL instance =
while keeping it to non-NULL instance in PlatformInitPostMem.

Scenario #2:

A PEIM is built that checks whether the boot mode is S3. If so, it calls Pe=
iInstallSmmAccessPpi(). A particular platform does not support S3, therefor=
e, it links BaseSmmAccessLibNull as its library instance for SmmAccessLib.

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Sure.<br /><br />Scenario #1:<br /><br />MinPlatformPkg/PlatformInit/Platfo=
rmInitPei/PlatformInitPreMem.inf and MinPlatormPkg/PlatformInit/PlatformIni=
tPei/PlatformInitPostMem.inf both link against an instance of BoardInitLib.=
<br /><br />Many boards link against a single BoardInitLib instance. See ex=
ample - https://github.com/tianocore/edk2-platforms/blob/cd4e6b716c7d1bcde9=
4035e7dce14b53a553e103/Platform/Intel/KabylakeOpenBoardPkg/KabylakeRvp3/Ope=
nBoardPkg.dsc#L203<br /><br />That BoardInitLib instance may link against S=
mmAccessLib. PlatformInitPreMem may wish to library class override the SmmA=
ccessLib to the NULL instance while keeping it to non-NULL instance in Plat=
formInitPostMem.<br /><br />Scenario #2:<br /><br />A PEIM is built that ch=
ecks whether the boot mode is S3. If so, it calls PeiInstallSmmAccessPpi().=
 A particular platform does not support S3, therefore, it links BaseSmmAcce=
ssLibNull as its library instance for SmmAccessLib.

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