From 25a2664625f892e4a35cdb57a567e060bcde043c Mon Sep 17 00:00:00 2001
From: Joseph Shifflett <joseph.shifflett@hpe.com>
Date: Tue, 6 Oct 2015 20:55:31 +0000
Subject: MdeModulePkg: exit pci function loops early if device is not
 multi-function

When looping through all PCI functions, code should not look for functions
1-7 if function 0 is not present or if function 0 indicates the device is
not multifunction.  Prior to this fix the code would use stale data in a
buffer to determine if a device is multifunction even if function 0 is not
present.  This fixes a code bug and provides very small performance
improvements.

PCI 2.3 Specification states: They [multifunction devices] are also
required to always implement function 0 in the device. Implementing other
functions is optional and may be assigned in any order.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Joseph Shifflett <joseph.shifflett@hpe.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18574 6f19259b-4bc3-4df7-8a09-765794883524
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c        |  8 ++++++++
 MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c | 16 ++++++++++++++++
 MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c               |  8 ++++++++
 3 files changed, 32 insertions(+)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c
index 7329143136..597c0834e0 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.c
@@ -2,6 +2,7 @@
   PCI eunmeration implementation on entire PCI bus system for PCI Bus module.
 
 Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>
+(C) Copyright 2015 Hewlett Packard Enterprise Development LP<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
@@ -407,6 +408,13 @@ PciAssignBusNumber (
                 Func
                 );
 
+      if (EFI_ERROR (Status) && Func == 0) {
+        //
+        // go to next device if there is no Function 0
+        //
+        break;
+      }
+
       if (!EFI_ERROR (Status)   &&
           (IS_PCI_BRIDGE (&Pci) || IS_CARDBUS_BRIDGE (&Pci))) {
 
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
index f46025e2f6..f7aea4fd80 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
@@ -2,6 +2,7 @@
   PCI emumeration support functions implementation for PCI Bus module.
 
 Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+(C) Copyright 2015 Hewlett Packard Enterprise Development LP<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
@@ -119,6 +120,14 @@ PciPciDeviceInfoCollector (
                  (UINT8) Device,
                  (UINT8) Func
                  );
+
+      if (EFI_ERROR (Status) && Func == 0) {
+        //
+        // go to next device if there is no Function 0
+        //
+        break;
+      }
+
       if (!EFI_ERROR (Status)) {
 
         //
@@ -2597,6 +2606,13 @@ ResetAllPpbBusNumber (
                  Func
                  );
 
+      if (EFI_ERROR (Status) && Func == 0) {
+        //
+        // go to next device if there is no Function 0
+        //
+        break;
+      }
+
       if (!EFI_ERROR (Status) && (IS_PCI_BRIDGE (&Pci))) {
 
         Register  = 0;
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
index b3d91a8d30..3e275e34ec 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
@@ -2,6 +2,7 @@
   Internal library implementation for PCI Bus module.
 
 Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>
+(C) Copyright 2015 Hewlett Packard Enterprise Development LP<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
@@ -1022,6 +1023,13 @@ PciScanBus (
                 Func
                 );
 
+      if (EFI_ERROR (Status) && Func == 0) {
+        //
+        // go to next device if there is no Function 0
+        //
+        break;
+      }
+
       if (EFI_ERROR (Status)) {
         continue;
       }
-- 
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