[PATCH] SecurityPkg Tcg2Pei: Add comments into LogHashEvent()

[Star Zeng <star.zeng@intel.com>]

Add comments into LogHashEvent() to describe the usage
of GetDigestListSize (DigestList).

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Chao Zhang <chao.b.zhang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 SecurityPkg/Tcg/Tcg2Pei/Tcg2Pei.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/SecurityPkg/Tcg/Tcg2Pei/Tcg2Pei.c b/SecurityPkg/Tcg/Tcg2Pei/Tcg2Pei.c
index 377f8d9fe45b..209d843245e4 100644
--- a/SecurityPkg/Tcg/Tcg2Pei/Tcg2Pei.c
+++ b/SecurityPkg/Tcg/Tcg2Pei/Tcg2Pei.c
@@ -317,6 +317,10 @@ LogHashEvent (
         }
         break;
       case EFI_TCG2_EVENT_LOG_FORMAT_TCG_2:
+        //
+        // Use GetDigestListSize (DigestList) in the GUID HOB DataLength calculation
+        // to reserve enough buffer to hold TPML_DIGEST_VALUES compact binary.
+        //
         HobData = BuildGuidHob (
                    &gTcgEvent2EntryHobGuid,
                    sizeof(TcgPcrEvent2->PCRIndex) + sizeof(TcgPcrEvent2->EventType) + GetDigestListSize (DigestList) + sizeof(TcgPcrEvent2->EventSize) + NewEventHdr->EventSize
-- 
2.7.0.windows.1