As per ACPI Spec 6.5+ Table 5-9 if xDSDT is avaialble,
it should be used first. Handle required flow when xDSDT
is abscent or present.

Test: Tested on RISCV64 Qemu platform with xDSDT and booted to
linux kernel.

Cc: Liming Gao <gaolim...@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang....@intel.com>
Cc: Dandan Bi <dandan...@intel.com>
Signed-off-by: Dhaval Sharma <dha...@rivosinc.com>
---

Notes:
    v2:
    - Added proper indentation for else if

 MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c | 22 
+++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c 
b/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c
index e09bc9b704f5..ead8376177c9 100644
--- a/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c
+++ b/MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c
@@ -1892,14 +1892,22 @@ InstallAcpiTableFromHob (
           }
         }
 
-        if (((EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE *)ChildTable)->Dsdt != 
0) {
+        //
+        // First check if xDSDT is available that is preferred as per
+        // ACPI Spec 6.5+ Table 5-9 X_DSDT definition
+        //
+        if (((EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE *)ChildTable)->XDsdt 
!= 0) {
+          TableToInstall = (VOID 
*)(UINTN)((EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE *)ChildTable)->XDsdt;
+        } else if (((EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE 
*)ChildTable)->Dsdt != 0) {
           TableToInstall = (VOID 
*)(UINTN)((EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE *)ChildTable)->Dsdt;
-          Status         = AddTableToList (AcpiTableInstance, TableToInstall, 
TRUE, Version, TRUE, &TableKey);
-          if (EFI_ERROR (Status)) {
-            DEBUG ((DEBUG_ERROR, "InstallAcpiTableFromHob: Fail to add ACPI 
table DSDT\n"));
-            ASSERT_EFI_ERROR (Status);
-            break;
-          }
+        } else {
+          break;
+        }
+        Status = AddTableToList (AcpiTableInstance, TableToInstall, TRUE, 
Version, TRUE, &TableKey);
+        if (EFI_ERROR (Status)) {
+          DEBUG ((DEBUG_ERROR, "InstallAcpiTableFromHob: Fail to add ACPI 
table DSDT\n"));
+          ASSERT_EFI_ERROR (Status);
+          break;
         }
       }
     }
-- 
2.39.2



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