[PATCH] MdeModulePkg/AcpiTableDxe: Not make FADT.{DSDT, X_DSDT} mutual exclusion

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

198a46d768fb90d2f9b16e26451b4814e7469eaf improved the DSDT and X_DSDT
fields mutual exclusion by checking FADT revision, but that breaks
some OS that has assumption to only consume X_DSDT field even the
DSDT address is < 4G.

To have better compatibility, this patch is to update the code to not
make FADT.{DSDT,X_DSDT} mutual exclusion, but always set both DSDT and
X_DSDT fields in the FADT when the DSDT address is < 4G.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>

NOTE: This patch comes out from the discussion at
https://lists.01.org/pipermail/edk2-devel/2017-March/008580.html.
---
 .../Acpi/AcpiTableDxe/AcpiTableProtocol.c          | 88 +++++++++-------------
 1 file changed, 34 insertions(+), 54 deletions(-)

diff --git a/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c b/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c
index 4bb848df5203..a4fd9aff845d 100644
--- a/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c
+++ b/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c
@@ -432,50 +432,6 @@ ReallocateAcpiTableBuffer (
 }
 
 /**
-  Determine whether the FADT table passed in as parameter requires mutual
-  exclusion between the DSDT and X_DSDT fields. (That is, whether there exists
-  an explicit requirement that at most one of those fields is permitted to be
-  nonzero.)
-
-  @param[in] Fadt  The EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE object to
-                   check.
-
-  @retval TRUE     Fadt requires mutual exclusion between DSDT and X_DSDT.
-  @retval FALSE    Otherwise.
-**/
-BOOLEAN
-RequireDsdtXDsdtExclusion (
-  IN EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE *Fadt
-  )
-{
-  //
-  // Mantis ticket #1393 was addressed in ACPI 5.1 Errata B. Unfortunately, we
-  // can't tell apart 5.1 Errata A and 5.1 Errata B just from looking at the
-  // FADT table. Therefore let's require exclusion for table versions >= 5.1.
-  //
-  // While this needlessly covers 5.1 and 5.1A too, it is safer to require
-  // DSDT<->X_DSDT exclusion for lax (5.1, 5.1A) versions of the spec than to
-  // permit DSDT<->X_DSDT duplication for strict (5.1B) versions of the spec.
-  //
-  // The same applies to 6.0 vs. 6.0A. While 6.0 does not require the
-  // exclusion, 6.0A and 6.1 do. Since we cannot distinguish 6.0 from 6.0A
-  // based on just the FADT, we lump 6.0 in with the rest of >= 5.1.
-  //
-  if ((Fadt->Header.Revision < 5) ||
-      ((Fadt->Header.Revision == 5) &&
-       (((EFI_ACPI_5_1_FIXED_ACPI_DESCRIPTION_TABLE *)Fadt)->MinorVersion == 0))) {
-    //
-    // version <= 5.0
-    //
-    return FALSE;
-  }
-  //
-  // version >= 5.1
-  //
-  return TRUE;
-}
-
-/**
   This function adds an ACPI table to the table list.  It will detect FACS and
   allocate the correct type of memory and properly align the table.
 
@@ -692,11 +648,23 @@ AddTableToList (
       }
       if ((UINT64)(UINTN)AcpiTableInstance->Dsdt3 < BASE_4GB) {
         AcpiTableInstance->Fadt3->Dsdt = (UINT32) (UINTN) AcpiTableInstance->Dsdt3;
-        if (RequireDsdtXDsdtExclusion (AcpiTableInstance->Fadt3)) {
-          Buffer64 = 0;
-        } else {
-          Buffer64 = AcpiTableInstance->Fadt3->Dsdt;
-        }
+        //
+        // Comment block "the caller installs the tables in "DSDT, FADT" order"
+        // The below comments are also in "the caller installs the tables in "FADT, DSDT" order" comment block.
+        //
+        // The ACPI specification, up to and including revision 5.1 Errata A,
+        // allows the DSDT and X_DSDT fields to be both set in the FADT.
+        // (Obviously, this only makes sense if the DSDT address is representable in 4 bytes.)
+        // Starting with 5.1 Errata B, specifically for Mantis 1393 <https://mantis.uefi.org/mantis/view.php?id=1393>,
+        // the spec requires at most one of DSDT and X_DSDT fields to be set to a nonzero value,
+        // but strangely an exception is 6.0 that has no this requirement.
+        //
+        // Here we do not make the DSDT and X_DSDT fields mutual exclusion conditionally
+        // by checking FADT revision, but always set both DSDT and X_DSDT fields in the FADT
+        // to have better compatibility as some OS may have assumption to only consume X_DSDT
+        // field even the DSDT address is < 4G.
+        //
+        Buffer64 = AcpiTableInstance->Fadt3->Dsdt;
       } else {
         AcpiTableInstance->Fadt3->Dsdt = 0;
         Buffer64 = (UINT64) (UINTN) AcpiTableInstance->Dsdt3;
@@ -896,11 +864,23 @@ AddTableToList (
       if (AcpiTableInstance->Fadt3 != NULL) {
         if ((UINT64)(UINTN)AcpiTableInstance->Dsdt3 < BASE_4GB) {
           AcpiTableInstance->Fadt3->Dsdt = (UINT32) (UINTN) AcpiTableInstance->Dsdt3;
-          if (RequireDsdtXDsdtExclusion (AcpiTableInstance->Fadt3)) {
-            Buffer64 = 0;
-          } else {
-            Buffer64 = AcpiTableInstance->Fadt3->Dsdt;
-          }
+          //
+          // Comment block "the caller installs the tables in "FADT, DSDT" order"
+          // The below comments are also in "the caller installs the tables in "DSDT, FADT" order" comment block.
+          //
+          // The ACPI specification, up to and including revision 5.1 Errata A,
+          // allows the DSDT and X_DSDT fields to be both set in the FADT.
+          // (Obviously, this only makes sense if the DSDT address is representable in 4 bytes.)
+          // Starting with 5.1 Errata B, specifically for Mantis 1393 <https://mantis.uefi.org/mantis/view.php?id=1393>,
+          // the spec requires at most one of DSDT and X_DSDT fields to be set to a nonzero value,
+          // but strangely an exception is 6.0 that has no this requirement.
+          //
+          // Here we do not make the DSDT and X_DSDT fields mutual exclusion conditionally
+          // by checking FADT revision, but always set both DSDT and X_DSDT fields in the FADT
+          // to have better compatibility as some OS may have assumption to only consume X_DSDT
+          // field even the DSDT address is < 4G.
+          //
+          Buffer64 = AcpiTableInstance->Fadt3->Dsdt;
         } else {
           AcpiTableInstance->Fadt3->Dsdt = 0;
           Buffer64 = (UINT64) (UINTN) AcpiTableInstance->Dsdt3;
-- 
2.7.0.windows.1