MdeModulePkg/AcpiTableDxe: Prefer xDSDT over DSDT when installing tables

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

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

Cc: Liming Gao <[email protected]>
Cc: Zhiguang Liu <[email protected]>
Cc: Dandan Bi <[email protected]>
Cc: Pedro Falcato <[email protected]>
Signed-off-by: Dhaval Sharma <[email protected]>
Acked-by: Chasel Chiu <chasel.chiu@...>
Reviewed-by: Liming Gao <[email protected]>

MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c

@@ -1906,14 +1906,24 @@ InstallAcpiTableFromHob (
           }
         }
 
-        if (((EFI_ACPI_3_0_FIXED_ACPI_DESCRIPTION_TABLE *)ChildTable)->Dsdt != 0) {
+        //
+        // First check if xDSDT is available, as 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 {
+          DEBUG ((DEBUG_ERROR, "DSDT table not found\n"));
+          continue;
+        }
+
+        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;
         }
       }
     }