From c70637de12e0d5cee78ebf5a0b5d09cdb1db53c9 Mon Sep 17 00:00:00 2001
From: Phil Noh <Phil.Noh@amd.com>
Date: Thu, 25 Jun 2026 15:41:25 -0500
Subject: [PATCH] MdeModulePkg/PciBusDxe: Honor SpecificFlag for PMem64 in
 UpdatePciInfo

When UpdatePciInfo() downgrades a PciBarTypePMem64 BAR to a 32-bit type
via EFI_INCOMPATIBLE_PCI_DEVICE_SUPPORT_PROTOCOL, it unconditionally
assigns PciBarTypePMem32 regardless of SpecificFlag, placing the BAR in
the prefetchable bridge window even when the platform intended the
non-prefetchable window.

The ACPI resource descriptor's SpecificFlag field encodes the intended
prefetchability of the constrained resource, using the bit:
EFI_ACPI_MEMORY_RESOURCE_SPECIFIC_FLAG_CACHEABLE_PREFETCHABLE.

Fix this by checking the bit in SpecificFlag to select PciBarTypePMem32 or
PciBarTypeMem32, consistent with DumpPpbPaddingResource() in
PciEnumeratorSupport.c that uses the bit as the sole discriminator
between the two 32-bit BAR types.

Signed-off-by: Phil Noh <Phil.Noh@amd.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
index a0f86f2806..ae94462f60 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
@@ -4,7 +4,7 @@
 Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.<BR>
 Copyright (c) 2006 - 2021, Intel Corporation. All rights reserved.<BR>
 (C) Copyright 2015 Hewlett Packard Enterprise Development LP<BR>
-Copyright (C) 2023 Advanced Micro Devices, Inc. All rights reserved.<BR>
+Copyright (C) 2023 - 2026 Advanced Micro Devices, Inc. All rights reserved.<BR>
 SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -1595,7 +1595,14 @@ UpdatePciInfo (
             if (PciIoDevice->PciBar[BarIndex].BarType == PciBarTypePMem64) {
               switch (Ptr->AddrSpaceGranularity) {
                 case 32:
-                  PciIoDevice->PciBar[BarIndex].BarType = PciBarTypePMem32;
+                  if ((Ptr->SpecificFlag & EFI_ACPI_MEMORY_RESOURCE_SPECIFIC_FLAG_CACHEABLE_PREFETCHABLE) ==
+                      EFI_ACPI_MEMORY_RESOURCE_SPECIFIC_FLAG_CACHEABLE_PREFETCHABLE)
+                  {
+                    PciIoDevice->PciBar[BarIndex].BarType = PciBarTypePMem32;
+                  } else {
+                    PciIoDevice->PciBar[BarIndex].BarType = PciBarTypeMem32;
+                  }
+
                 case 64:
                   PciIoDevice->PciBar[BarIndex].BarTypeFixed = TRUE;
                   break;