MdeModulePkg/PciHostBridgeDxe: Ignore unsupported I/O BARs.

PCIe enumeration fails if an endpoint requests I/O space BARs
and the Root Bridge does not support I/O space. While I/O space is
traditionally supported in x86_64, platforms using an Arm
architecture may or may not support I/O space.

This change adds logic allowing the platform to detect I/O space
support for each Root Bridge and prevent submission of the required
I/O resources for allocation when unsupported. Endpoints will not
receive I/O resources, but they will continue to receive Memory
BAR resources.

Signed-off-by: Michael Escue <[email protected]>

Author: michaelescue

MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciHostBridge.c

@@ -1568,7 +1568,15 @@ SubmitResources (
 
         RootBridge->ResAllocNode[Type].Length    = Descriptor->AddrLen;
         RootBridge->ResAllocNode[Type].Alignment = Descriptor->AddrRangeMax;
-        RootBridge->ResAllocNode[Type].Status    = ResSubmitted;
+        //
+        // If the PCI root bridge does not suport IO Space, do not submit requested resources
+        // for allocation.
+        //
+        if ((Type == TypeIo) && (RootBridge->Io.Base > RootBridge->Io.Limit)) {
+          RootBridge->ResAllocNode[Type].Status = ResNone;
+        } else {
+          RootBridge->ResAllocNode[Type].Status = ResSubmitted;
+        }
       }
 
       RootBridge->ResourceSubmitted = TRUE;