DynamicTablesPkg: AmlLib: AmlAddPrtEntry() to handle GSI

In ACPI 6.4, s6.2.13, _PRT objects describing PCI legacy interrupts
can be defined following 2 models.
In the first model, _PRT entries reference link devices. Link devices
then describe interrupts. This allows to dynamically modify
interrupts through _SRS and _PRS objects and to choose exactly the
interrupt type (level/edge triggered, active high/low).
In the second model, interrupt numbers are described in the _PRT entry.
The interrupt type is then assumed by the OS.

AmlAddPrtEntry() currently only handles the first model. Make
changes to also handle the second model.

Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

DynamicTablesPkg/Library/Common/AmlLib/CodeGen/AmlCodeGen.c

@@ -1,7 +1,7 @@
 /** @file
   AML Code Generation.
 
-  Copyright (c) 2020 - 2021, Arm Limited. All rights reserved.<BR>
+  Copyright (c) 2020 - 2022, Arm Limited. All rights reserved.<BR>
 
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
@@ -881,6 +881,9 @@ AmlCodeGenNameResourceTemplate (
                // interrupt, so let it to index 0.
     }
 
+  The 2 models described in ACPI 6.4, s6.2.13 "_PRT (PCI Routing Table)" can
+  be generated by this function. The example above matches the first model.
+
   The package is added at the tail of the list of the input _PRT node
   name:
     Name (_PRT, Package () {
@@ -901,8 +904,10 @@ AmlCodeGenNameResourceTemplate (
   @param [in]  Pin            PCI pin number of the device (0-INTA ... 3-INTD).
                               Must be between 0-3.
   @param [in]  LinkName       Link Name, i.e. device in the AML NameSpace
-                              describing the interrupt used.
+                              describing the interrupt used. The input string
-                              The input string is copied.
+                              is copied.
+                              If NULL, generate 0 in the 'Source' field (cf.
+                              second model, using GSIV).
   @param [in]  SourceIndex    Source index or GSIV.
   @param [in]  PrtNameNode    Prt Named node to add the object to ....
 
@@ -930,7 +935,6 @@ AmlAddPrtEntry (
   AML_DATA_NODE  *DataNode;
 
   if ((Pin > 3)                 ||
-      (LinkName == NULL)        ||
       (PrtNameNode == NULL)     ||
       (AmlGetNodeType ((AML_NODE_HANDLE)PrtNameNode) != EAmlNodeObject) ||
       (!AmlNodeHasOpCode (PrtNameNode, AML_NAME_OP, 0))                 ||
@@ -999,42 +1003,59 @@ AmlAddPrtEntry (
 
   NewElementNode = NULL;
 
-  Status = ConvertAslNameToAmlName (LinkName, &AmlNameString);
+  if (LinkName != NULL) {
-  if (EFI_ERROR (Status)) {
+    Status = ConvertAslNameToAmlName (LinkName, &AmlNameString);
-    ASSERT (0);
+    if (EFI_ERROR (Status)) {
-    goto error_handler;
+      ASSERT_EFI_ERROR (Status);
+      goto error_handler;
+    }
+
+    Status = AmlGetNameStringSize (AmlNameString, &AmlNameStringSize);
+    if (EFI_ERROR (Status)) {
+      ASSERT_EFI_ERROR (Status);
+      goto error_handler;
+    }
+
+    Status = AmlCreateDataNode (
+               EAmlNodeDataTypeNameString,
+               (UINT8 *)AmlNameString,
+               AmlNameStringSize,
+               &DataNode
+               );
+    if (EFI_ERROR (Status)) {
+      ASSERT_EFI_ERROR (Status);
+      goto error_handler;
+    }
+
+    // AmlNameString will be freed be fore returning.
+
+    Status = AmlVarListAddTail (
+               (AML_NODE_HANDLE)PackageNode,
+               (AML_NODE_HANDLE)DataNode
+               );
+    if (EFI_ERROR (Status)) {
+      ASSERT_EFI_ERROR (Status);
+      goto error_handler;
+    }
+
+    DataNode = NULL;
+  } else {
+    Status = AmlCodeGenInteger (0, &NewElementNode);
+    if (EFI_ERROR (Status)) {
+      ASSERT_EFI_ERROR (Status);
+      goto error_handler;
+    }
+
+    Status = AmlVarListAddTail (
+               (AML_NODE_HANDLE)PackageNode,
+               (AML_NODE_HANDLE)NewElementNode
+               );
+    if (EFI_ERROR (Status)) {
+      ASSERT_EFI_ERROR (Status);
+      goto error_handler;
+    }
   }
 
-  Status = AmlGetNameStringSize (AmlNameString, &AmlNameStringSize);
-  if (EFI_ERROR (Status)) {
-    ASSERT (0);
-    goto error_handler;
-  }
-
-  Status = AmlCreateDataNode (
-             EAmlNodeDataTypeNameString,
-             (UINT8 *)AmlNameString,
-             AmlNameStringSize,
-             &DataNode
-             );
-  if (EFI_ERROR (Status)) {
-    ASSERT (0);
-    goto error_handler;
-  }
-
-  // AmlNameString will be freed before returning.
-
-  Status = AmlVarListAddTail (
-             (AML_NODE_HANDLE)PackageNode,
-             (AML_NODE_HANDLE)DataNode
-             );
-  if (EFI_ERROR (Status)) {
-    ASSERT (0);
-    goto error_handler;
-  }
-
-  DataNode = NULL;
-
   Status = AmlCodeGenInteger (SourceIndex, &NewElementNode);
   if (EFI_ERROR (Status)) {
     ASSERT (0);