[PATCH] IntelSiliconPkg IntelVTdDxe: Check HeaderType if func 0 is implemented

[Star Zeng <star.zeng@intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1169

Current code checks HeaderType of Function 0 even Function 0 is not
implemented. HeaderType value will be 0xFF if Function 0 is not
implemented, then MaxFunction will be set to PCI_MAX_FUNC + 1.

The code can be optimized to only check HeaderType if Function 0 is
implemented.

Test done:
With this patch, the result is same with the result after the patch at
https://lists.01.org/pipermail/edk2-devel/2018-September/029623.html.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Rangasai V Chaganty <rangasai.v.chaganty@intel.com>
Cc: Tomson Chang <tomson.chang@intel.com>
Cc: Jenny Huang <jenny.huang@intel.com>
Cc: Amy Chan <amy.chan@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c b/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
index 305995de032c..6ae5df589c1e 100644
--- a/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
+++ b/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
@@ -231,19 +231,13 @@ ScanPciBus (
   UINT8                   HeaderType;
   UINT8                   BaseClass;
   UINT8                   SubClass;
-  UINT32                  MaxFunction;
   UINT16                  VendorID;
   UINT16                  DeviceID;
   EFI_STATUS              Status;
 
   // Scan the PCI bus for devices
-  for (Device = 0; Device < PCI_MAX_DEVICE + 1; Device++) {
-    HeaderType = PciSegmentRead8 (PCI_SEGMENT_LIB_ADDRESS(Segment, Bus, Device, 0, PCI_HEADER_TYPE_OFFSET));
-    MaxFunction = PCI_MAX_FUNC + 1;
-    if ((HeaderType & HEADER_TYPE_MULTI_FUNCTION) == 0x00) {
-      MaxFunction = 1;
-    }
-    for (Function = 0; Function < MaxFunction; Function++) {
+  for (Device = 0; Device <= PCI_MAX_DEVICE; Device++) {
+    for (Function = 0; Function <= PCI_MAX_FUNC; Function++) {
       VendorID  = PciSegmentRead16 (PCI_SEGMENT_LIB_ADDRESS(Segment, Bus, Device, Function, PCI_VENDOR_ID_OFFSET));
       DeviceID  = PciSegmentRead16 (PCI_SEGMENT_LIB_ADDRESS(Segment, Bus, Device, Function, PCI_DEVICE_ID_OFFSET));
       if (VendorID == 0xFFFF && DeviceID == 0xFFFF) {
@@ -275,6 +269,16 @@ ScanPciBus (
           }
         }
       }
+
+      if (Function == 0) {
+        HeaderType = PciSegmentRead8 (PCI_SEGMENT_LIB_ADDRESS(Segment, Bus, Device, 0, PCI_HEADER_TYPE_OFFSET));
+        if ((HeaderType & HEADER_TYPE_MULTI_FUNCTION) == 0x00) {
+          //
+          // It is not a multi-function device, do not scan other functions.
+          //
+          break;
+        }
+      }
     }
   }
 
-- 
2.7.0.windows.1