UefiCpuPkg/AcpiCpuData: update comments on register table fields

After commit e992cc3f4859 ("UefiCpuPkg PiSmmCpuDxeSmm: Reduce SMRAM
consumption in CpuS3.c", 2021-01-11), it is valid for a CPU S3 Data DXE
Driver to set "ACPI_CPU_DATA.PreSmmInitRegisterTable" and/or
"ACPI_CPU_DATA.RegisterTable" to 0, in case none of the CPUs needs a
register table of the corresponding kind, during S3 resume.

Document this fact in the "UefiCpuPkg/Include/AcpiCpuData.h" header file.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3159
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210119155440.2262-3-lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/UefiCpuPkg/Include/AcpiCpuData.h b/UefiCpuPkg/Include/AcpiCpuData.h
index b5a69ad80c..62a01b2c6b 100644
--- a/UefiCpuPkg/Include/AcpiCpuData.h
+++ b/UefiCpuPkg/Include/AcpiCpuData.h
@@ -178,6 +178,8 @@ typedef struct {
   // If TableLength is > 0, then elements of RegisterTableEntry are used to

   // initialize the CPU that matches InitialApicId, during an ACPI S3 resume,

   // before SMBASE relocation is performed.

+  // If a register table is not required for any one of the CPUs, then

+  // PreSmmInitRegisterTable may be set to 0.

   //

   EFI_PHYSICAL_ADDRESS  PreSmmInitRegisterTable;

   //

@@ -187,6 +189,8 @@ typedef struct {
   // If TableLength is > 0, then elements of RegisterTableEntry are used to

   // initialize the CPU that matches InitialApicId, during an ACPI S3 resume,

   // after SMBASE relocation is performed.

+  // If a register table is not required for any one of the CPUs, then

+  // RegisterTable may be set to 0.

   //

   EFI_PHYSICAL_ADDRESS  RegisterTable;

   //