[patch 3/3] MdePkg: Handle AcpiExp device path when optional para is not specified

[Dandan Bi <dandan.bi@intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1243

AcpiExp text device path: AcpiExp(HID,CID,UIDSTR)
And according to UEFI spec, the CID parameter is optional
and has a default value of 0. But current implementation
miss to check following cases for the AcpiExp.
FromText:when text device is AcpiExp(HID,,UIDSTR)/AcpiExp(HID,0,UIDSTR)
ToText: when the CID is 0 in the node structure

This commit is to do the enhancement.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
---
 .../UefiDevicePathLib/DevicePathFromText.c    | 11 ++++++++-
 .../UefiDevicePathLib/DevicePathToText.c      | 23 +++++++++++++------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/MdePkg/Library/UefiDevicePathLib/DevicePathFromText.c b/MdePkg/Library/UefiDevicePathLib/DevicePathFromText.c
index 4b49e341c7..b759146b72 100644
--- a/MdePkg/Library/UefiDevicePathLib/DevicePathFromText.c
+++ b/MdePkg/Library/UefiDevicePathLib/DevicePathFromText.c
@@ -917,11 +917,20 @@ DevPathFromTextAcpiExp (
                                                   ACPI_EXTENDED_DP,
                                                   Length
                                                   );
 
   AcpiEx->HID = EisaIdFromText (HIDStr);
-  AcpiEx->CID = EisaIdFromText (CIDStr);
+  //
+  // According to UEFI spec, the CID parametr is optional and has a default value of 0.
+  // So when the CID parametr is not specified or specified as 0 in the text device node.
+  // Set the CID to 0 in the ACPI extension device path structure.
+  //
+  if (*CIDStr == L'\0' || *CIDStr == L'0') {
+    AcpiEx->CID = 0;
+  } else {
+    AcpiEx->CID = EisaIdFromText (CIDStr);
+  }
   AcpiEx->UID = 0;
 
   AsciiStr = (CHAR8 *) ((UINT8 *)AcpiEx + sizeof (ACPI_EXTENDED_HID_DEVICE_PATH));
   //
   // HID string is NULL
diff --git a/MdePkg/Library/UefiDevicePathLib/DevicePathToText.c b/MdePkg/Library/UefiDevicePathLib/DevicePathToText.c
index 7ad9eadf6c..cdcdb3623a 100644
--- a/MdePkg/Library/UefiDevicePathLib/DevicePathToText.c
+++ b/MdePkg/Library/UefiDevicePathLib/DevicePathToText.c
@@ -478,17 +478,26 @@ DevPathToTextAcpiEx (
 
   if ((*HIDStr == '\0') && (*CIDStr == '\0') && (*UIDStr != '\0')) {
     //
     // use AcpiExp()
     //
-    UefiDevicePathLibCatPrint (
-      Str,
-      L"AcpiExp(%s,%s,%a)",
-      HIDText,
-      CIDText,
-      UIDStr
-      );
+    if (AcpiEx->CID == 0) {
+      UefiDevicePathLibCatPrint (
+        Str,
+        L"AcpiExp(%s,0,%a)",
+        HIDText,
+        UIDStr
+       );
+    } else {
+      UefiDevicePathLibCatPrint (
+        Str,
+        L"AcpiExp(%s,%s,%a)",
+        HIDText,
+        CIDText,
+        UIDStr
+       );
+    }
   } else {
     if (AllowShortcuts) {
       //
       // display only
       //
-- 
2.18.0.windows.1