UEFI Capsule flag check for ScatterGatherList

[davidhuziji]

Hi all,

Sorry if it is a dumb question.

I'm quite confused by the descriptions of ScatterGatherList in UEFI spec. When I check EDK2 code as a reference, I notice that EDK2 and EDK2-test implement 2 different behaviors to validate ScatterGatherList.

• In EDK2, ScatterGatherList shall not be NULL as long as CAPSULE_FLAGS_PERSIST_ACROSS_RESET is set: https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Universal/CapsuleRuntimeDxe/CapsuleService.c#L175
• In the meantime, in EDK2-test, both CAPSULE_FLAGS_PERSIST_ACROSS_RESET and CAPSULE_FLAGS_POPULATE_SYSTEM_TABLE are set to perform the same validation: https://github.com/tianocore/edk2-test/blob/master/uefi-sct/SctPkg/TestCase/UEFI/EFI/RuntimeServices/MiscRuntimeServices/BlackBoxTest/MiscRuntimeServicesBBTestConformance.c#L124

Can I ask for clarity about setting which flag(s) suggest that ScatterGatherList shall not be NULL?
Is ScatterGatherList also used in UEFI capsule update when CAPSULE_FLAGS_POPULATE_SYSTEM_TABLE is not set?

Thank you.

[spbrogan]

I assume the edk2 code is incomplete and/or use case isn't supported. In the platforms I build we do not use this type of capsule. Using CAPSULE_FLAGS_POPULATE_SYSTEM_TABLE is not something I have seen used for anything other than a platform defined use case. Capsules for 3rd party (not tightly coupled with motherboard builder/UEFI author) is not something with clear guidelines. FMP and ESRT has some mention of how it "could" work with option rom/3rd party, but I don't know of widespread usage.

If a capsule needs to be persisted across reset in system memory I would expect the ScatterGatherList is needed.