[PATCH v2 1/2] MdeModulePkg: Fixed extra 1 SR-IOV reserved bus

[Foster Nong <foster.nong@intel.com>]

Below code will calculate the reserved bus number for the each PF.

Based on the VF routing ID algorithm, PFRid and LastVF in below code
already sure that "All VFs and PFs must have distinct Routing IDs".
PF will be assigned Routing ID based on secBusNumber, ReservedBusNum
will add into SubBusNumber directly. So the SR-IOV device will be
assigned bus range as SecBusNumber ~ (SubBusNumber=(SecBusNumber +
ReservedBusNum)).
Thus "+1" in below code will cause extra 1 bus, and introduce a bus hole.

 PFRid  = EFI_PCI_RID (Bus, Device, Func);
 LastVF = PFRid + FirstVFOffset + (PciIoDevice->InitialVFs - 1) * VFStride;
 PciIoDevice->ReservedBusNum = (UINT16)(EFI_PCI_BUS_OF_RID (LastVF) -
 Bus + 1);

In SR-IOV spec, there is a note in section 2.1.2:
Note: Bus Numbers are a constrained resource. Devices are strongly
encouraged to avoid leaving “holes” in their Bus Number usage to avoid
wasting Bus Numbers

So the issue can be fixed with below code change.
  PciIoDevice->ReservedBusNum = (UINT16)(EFI_PCI_BUS_OF_RID (LastVF) -
  Bus);

https://bugzilla.tianocore.org/show_bug.cgi?id=4069

Signed-off-by: Foster Nong <foster.nong@intel.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
index eb250f6f7b..bc20da1f38 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
@@ -2425,7 +2425,7 @@ CreatePciIoDevice (
         //
         // Calculate ReservedBusNum for this PF
         //
-        PciIoDevice->ReservedBusNum = (UINT16)(EFI_PCI_BUS_OF_RID (LastVF) - Bus + 1);
+        PciIoDevice->ReservedBusNum = (UINT16)(EFI_PCI_BUS_OF_RID (LastVF) - Bus);
       }
 
       DEBUG ((
-- 
2.37.1.windows.1