[PATCH v2] MdeModulePkg/PciBusDxe: make OPROM BAR degradation configurable

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

The 'universal' PCI bus driver in MdeModulePkg contains a quirk to
degrade 64-bit PCI MMIO BARs to 32-bit in the presence of an option
ROM on the same PCI controller.

This quirk is highly specific to not just the X64 architecture in general,
but to the PC platform in particular, given that only X64 platforms that
require legacy PC BIOS compatibility require it. However, making the
quirk dependent on the presence of the legacy BIOS protocol met with
resistance, due to the fact that it introduces a dependency on the
IntelFrameworkModulePkg package.

So instead, make the quirk configurable, by introducing a feature flag PCD
which defaults to TRUE only for X64.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
v2: followed the suggestion of Andrew Fish to introduce a new feature flag
    PCD that controls the PCI BAR degradation behavior.

 MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf        |  1 +
 MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c | 76 ++++++++++----------
 MdeModulePkg/MdeModulePkg.dec                       | 12 ++++
 3 files changed, 52 insertions(+), 37 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf
index 330ccc8cbffc..fc49f3d9412c 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf
@@ -100,6 +100,7 @@ [FeaturePcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdPciBusHotplugDeviceSupport  ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdPciBridgeIoAlignmentProbe   ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdUnalignedPciIoEnable        ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdPciDegradeBarsForOptionRom  ## CONSUMES
 
 [Pcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdSrIovSystemPageSize         ## SOMETIMES_CONSUMES
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c
index b0632d53b82b..37dc03e90358 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c
@@ -1058,48 +1058,50 @@ DegradeResource (
   LIST_ENTRY           *NextChildNodeLink;
   PCI_RESOURCE_NODE    *ResourceNode;
 
-  //
-  // If any child device has both option ROM and 64-bit BAR, degrade its PMEM64/MEM64
-  // requests in case that if a legacy option ROM image can not access 64-bit resources.
-  //
-  ChildDeviceLink = Bridge->ChildList.ForwardLink;
-  while (ChildDeviceLink != NULL && ChildDeviceLink != &Bridge->ChildList) {
-    PciIoDevice = PCI_IO_DEVICE_FROM_LINK (ChildDeviceLink);
-    if (PciIoDevice->RomSize != 0) {
-      if (!IsListEmpty (&Mem64Node->ChildList)) {      
-        ChildNodeLink = Mem64Node->ChildList.ForwardLink;
-        while (ChildNodeLink != &Mem64Node->ChildList) {
-          ResourceNode = RESOURCE_NODE_FROM_LINK (ChildNodeLink);
-          NextChildNodeLink = ChildNodeLink->ForwardLink;
-
-          if ((ResourceNode->PciDev == PciIoDevice) &&
-              (ResourceNode->Virtual || !PciIoDevice->PciBar[ResourceNode->Bar].BarTypeFixed)
-              ) {
-            RemoveEntryList (ChildNodeLink);
-            InsertResourceNode (Mem32Node, ResourceNode);
+  if (FeaturePcdGet (PcdPciDegradeBarsForOptionRom)) {
+    //
+    // If any child device has both option ROM and 64-bit BAR, degrade its PMEM64/MEM64
+    // requests in case that if a legacy option ROM image can not access 64-bit resources.
+    //
+    ChildDeviceLink = Bridge->ChildList.ForwardLink;
+    while (ChildDeviceLink != NULL && ChildDeviceLink != &Bridge->ChildList) {
+      PciIoDevice = PCI_IO_DEVICE_FROM_LINK (ChildDeviceLink);
+      if (PciIoDevice->RomSize != 0) {
+        if (!IsListEmpty (&Mem64Node->ChildList)) {
+          ChildNodeLink = Mem64Node->ChildList.ForwardLink;
+          while (ChildNodeLink != &Mem64Node->ChildList) {
+            ResourceNode = RESOURCE_NODE_FROM_LINK (ChildNodeLink);
+            NextChildNodeLink = ChildNodeLink->ForwardLink;
+
+            if ((ResourceNode->PciDev == PciIoDevice) &&
+                (ResourceNode->Virtual || !PciIoDevice->PciBar[ResourceNode->Bar].BarTypeFixed)
+                ) {
+              RemoveEntryList (ChildNodeLink);
+              InsertResourceNode (Mem32Node, ResourceNode);
+            }
+            ChildNodeLink = NextChildNodeLink;
           }
-          ChildNodeLink = NextChildNodeLink;
-        }        
-      }
+        }
 
-      if (!IsListEmpty (&PMem64Node->ChildList)) {      
-        ChildNodeLink = PMem64Node->ChildList.ForwardLink;
-        while (ChildNodeLink != &PMem64Node->ChildList) {
-          ResourceNode = RESOURCE_NODE_FROM_LINK (ChildNodeLink);
-          NextChildNodeLink = ChildNodeLink->ForwardLink;
-
-          if ((ResourceNode->PciDev == PciIoDevice) &&
-              (ResourceNode->Virtual || !PciIoDevice->PciBar[ResourceNode->Bar].BarTypeFixed)
-              ) {
-            RemoveEntryList (ChildNodeLink);
-            InsertResourceNode (PMem32Node, ResourceNode);
+        if (!IsListEmpty (&PMem64Node->ChildList)) {
+          ChildNodeLink = PMem64Node->ChildList.ForwardLink;
+          while (ChildNodeLink != &PMem64Node->ChildList) {
+            ResourceNode = RESOURCE_NODE_FROM_LINK (ChildNodeLink);
+            NextChildNodeLink = ChildNodeLink->ForwardLink;
+
+            if ((ResourceNode->PciDev == PciIoDevice) &&
+                (ResourceNode->Virtual || !PciIoDevice->PciBar[ResourceNode->Bar].BarTypeFixed)
+                ) {
+              RemoveEntryList (ChildNodeLink);
+              InsertResourceNode (PMem32Node, ResourceNode);
+            }
+            ChildNodeLink = NextChildNodeLink;
           }
-          ChildNodeLink = NextChildNodeLink;
-        }        
-      }
+        }
 
+      }
+      ChildDeviceLink = ChildDeviceLink->ForwardLink;
     }
-    ChildDeviceLink = ChildDeviceLink->ForwardLink;
   }
 
   //
diff --git a/MdeModulePkg/MdeModulePkg.dec b/MdeModulePkg/MdeModulePkg.dec
index 8d90f169b26e..d8cb9c119598 100644
--- a/MdeModulePkg/MdeModulePkg.dec
+++ b/MdeModulePkg/MdeModulePkg.dec
@@ -749,6 +749,18 @@ [PcdsFeatureFlag]
   # @Prompt Turn on PS2 Mouse Extended Verification
   gEfiMdeModulePkgTokenSpaceGuid.PcdPs2MouseExtendedVerification|TRUE|BOOLEAN|0x00010075
 
+[PcdsFeatureFlag.X64]
+  ## Indicates whether 64-bit PCI MMIO BARs should degrade to 32-bit in the presence of an option ROM
+  #  On X64 platforms, Option ROMs may contain code that executes in the context of a legacy BIOS (CSM),
+  #  which requires that all PCI MMIO BARs are located below 4 GB
+  #   TRUE  - All PCI MMIO BARs of a device will be located below 4 GB if it has an option ROM
+  #   FALSE - PCI MMIO BARs of a device may be located above 4 GB even if it has an option ROM
+  # @Prompt Degrade 64-bit PCI MMIO BARs for legacy BIOS option ROMs
+  gEfiMdeModulePkgTokenSpaceGuid.PcdPciDegradeBarsForOptionRom|TRUE|BOOLEAN|0x0001003a
+
+[PcdsFeatureFlag.IA32, PcdsFeatureFlag.ARM, PcdsFeatureFlag.AARCH64]
+  gEfiMdeModulePkgTokenSpaceGuid.PcdPciDegradeBarsForOptionRom|FALSE|BOOLEAN|0x0001003a
+
 [PcdsFeatureFlag.IA32, PcdsFeatureFlag.X64]
   ## Indicates if DxeIpl should switch to long mode to enter DXE phase.
   #  It is assumed that 64-bit DxeCore is built in firmware if it is true; otherwise 32-bit DxeCore
-- 
2.7.4