IntelSiliconPkg IntelVTdDxe: Optimize when func 0 is not implemented

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

PCI spec:
They are also required to always implement function 0 in the device.
Implementing other functions is optional and may be assigned in any
order (i.e., a two-function device must respond to function 0 but
can choose any of the other possible function numbers (1-7) for the
second function).

This patch updates ScanPciBus() to not scan other functions if
function 0 is not implemented.

Test done:
Added debug code below in the second loop of ScanPciBus(),
compared the debug logs with and without this patch, many
non-0 unimplemented functions are skipped correctly.

  DEBUG ((
    DEBUG_INFO,
    "%a() B%02xD%02xF%02x VendorId: %04x DeviceId: %04x\n",
    __FUNCTION__,
    Bus,
    Device,
    Function,
    VendorID,
    DeviceID
    ));

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>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c b/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
index 36750b3f1d..305995de03 100644
--- a/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
+++ b/IntelSiliconPkg/Feature/VTd/IntelVTdDxe/PciInfo.c
@@ -1,6 +1,6 @@
 /** @file

 

-  Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>

+  Copyright (c) 2017 - 2018, Intel Corporation. All rights reserved.<BR>

   This program and the accompanying materials

   are licensed and made available under the terms and conditions of the BSD License

   which accompanies this distribution.  The full text of the license may be found at

@@ -247,6 +247,12 @@ ScanPciBus (
       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) {

+        if (Function == 0) {

+          //

+          // If function 0 is not implemented, do not scan other functions.

+          //

+          break;

+        }

         continue;

       }