[PATCH] MdeModulePkg/PciBusDxe: make BAR degradation dependent on OPROM presence

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

The practice of unconditionally degrading 64-bit PCI MMIO BARs to 32-bit
if the device in question happens to have an option ROM is based on
platform constraints, not architectural constraints, and really only makes
sense on Intel platforms that contain a CSM implementation.

So let's copy the OVMF code that checks for the presence of the legacy
BIOS protocol (&gEfiLegacyBiosProtocolGuid), and only perform the BAR
degradation if this protocol is installed.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.c             | 42 ++++++++++
 MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.h             |  1 +
 MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf        |  2 +
 MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c | 83 ++++++++++----------
 4 files changed, 88 insertions(+), 40 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.c
index a463bea80f3d..857f3e11b6bd 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.c
@@ -49,6 +49,39 @@ GLOBAL_REMOVE_IF_UNREFERENCED EFI_PCI_HOTPLUG_REQUEST_PROTOCOL mPciHotPlugReques
 };
 
 /**
+  Legacy BIOS installed callback
+
+  @param[in] Event      Event whose notification function is being invoked.
+  @param[in] Context    Pointer to the notification function's context.
+
+**/
+STATIC
+VOID
+EFIAPI
+LegacyBiosInstalledCallBack (
+  IN EFI_EVENT          Event,
+  IN VOID               *Context
+  )
+{
+  EFI_STATUS               Status;
+  EFI_LEGACY_BIOS_PROTOCOL *LegacyBios;
+
+  Status = gBS->LocateProtocol (&gEfiLegacyBiosProtocolGuid,
+                  NULL /* Registration */, (VOID **)&LegacyBios);
+  if (EFI_ERROR (Status)) {
+    return;
+  }
+
+  mLegacyBiosInstalled = TRUE;
+
+  //
+  // Close the event and deregister this callback.
+  //
+  Status = gBS->CloseEvent (Event);
+  ASSERT_EFI_ERROR (Status);
+}
+
+/**
   The Entry Point for PCI Bus module. The user code starts with this function.
 
   Installs driver module protocols and. Creates virtual device handles for ConIn,
@@ -72,6 +105,7 @@ PciBusEntryPoint (
 {
   EFI_STATUS  Status;
   EFI_HANDLE  Handle;
+  VOID        *Registration;
 
   //
   // Initializes PCI devices pool
@@ -91,6 +125,14 @@ PciBusEntryPoint (
              );
   ASSERT_EFI_ERROR (Status);
 
+  EfiCreateProtocolNotifyEvent (
+    &gEfiLegacyBiosProtocolGuid,
+    TPL_CALLBACK,
+    LegacyBiosInstalledCallBack,
+    NULL,
+    &Registration
+    );
+
   if (FeaturePcdGet (PcdPciBusHotplugDeviceSupport)) {
     //
     // If Hot Plug is supported, install EFI PCI Hot Plug Request protocol.
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.h b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.h
index b12d7ec5032f..2bf5695476a1 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.h
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.h
@@ -321,6 +321,7 @@ extern EFI_PCI_PLATFORM_PROTOCOL                    *gPciPlatformProtocol;
 extern EFI_PCI_OVERRIDE_PROTOCOL                    *gPciOverrideProtocol;
 extern BOOLEAN                                      mReserveIsaAliases;
 extern BOOLEAN                                      mReserveVgaAliases;
+extern BOOLEAN                                      mLegacyBiosInstalled;
 
 /**
   Macro that checks whether device is a GFX device.
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf
index 330ccc8cbffc..b843ccc49934 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciBusDxe.inf
@@ -66,6 +66,7 @@ [Sources]
 [Packages]
   MdePkg/MdePkg.dec
   MdeModulePkg/MdeModulePkg.dec
+  IntelFrameworkPkg/IntelFrameworkPkg.dec
 
 [LibraryClasses]
   PcdLib
@@ -95,6 +96,7 @@ [Protocols]
   gEfiPciRootBridgeIoProtocolGuid                 ## TO_START
   gEfiIncompatiblePciDeviceSupportProtocolGuid    ## SOMETIMES_CONSUMES
   gEfiLoadFile2ProtocolGuid                       ## SOMETIMES_PRODUCES
+  gEfiLegacyBiosProtocolGuid                      ## SOMETIMES_CONSUMES
 
 [FeaturePcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdPciBusHotplugDeviceSupport  ## CONSUMES
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c
index b0632d53b82b..6637625b210d 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciResourceSupport.c
@@ -17,9 +17,10 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 //
 // The default policy for the PCI bus driver is NOT to reserve I/O ranges for both ISA aliases and VGA aliases.
 //
-BOOLEAN mReserveIsaAliases = FALSE;
-BOOLEAN mReserveVgaAliases = FALSE;
-BOOLEAN mPolicyDetermined  = FALSE;
+BOOLEAN mReserveIsaAliases    = FALSE;
+BOOLEAN mReserveVgaAliases    = FALSE;
+BOOLEAN mPolicyDetermined     = FALSE;
+BOOLEAN mLegacyBiosInstalled  = FALSE;
 
 /**
   The function is used to skip VGA range.
@@ -1058,48 +1059,50 @@ 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 (mLegacyBiosInstalled) {
+    //
+    // 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;
   }
 
   //
-- 
2.7.4