From 68306ac2f2e7b85fc0d592248f68679139809b1a Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Tue, 14 Jul 2015 12:02:34 +0000
Subject: OvmfPkg: PciHostBridgeDxe: shorten search for extra root buses

QEMU provides an fw_cfg file called "etc/extra-pci-roots", containing a
little-endian UINT64 value that exposes the number of extra root buses. We
can use this value to terminate the scan as soon as we find the last extra
root bus.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17963 6f19259b-4bc3-4df7-8a09-765794883524
---
 OvmfPkg/PciHostBridgeDxe/PciHostBridge.c      | 22 +++++++++++++++++++++-
 OvmfPkg/PciHostBridgeDxe/PciHostBridgeDxe.inf |  2 ++
 2 files changed, 23 insertions(+), 1 deletion(-)

(limited to 'OvmfPkg')

diff --git a/OvmfPkg/PciHostBridgeDxe/PciHostBridge.c b/OvmfPkg/PciHostBridgeDxe/PciHostBridge.c
index 348664438d..efef2ed79e 100644
--- a/OvmfPkg/PciHostBridgeDxe/PciHostBridge.c
+++ b/OvmfPkg/PciHostBridgeDxe/PciHostBridge.c
@@ -15,6 +15,8 @@
 
 **/
 
+#include <Library/QemuFwCfgLib.h>
+
 #include "PciHostBridge.h"
 
 STATIC
@@ -207,6 +209,9 @@ InitializePciHostBridge (
   )
 {
   EFI_STATUS                  Status;
+  FIRMWARE_CONFIG_ITEM        FwCfgItem;
+  UINTN                       FwCfgSize;
+  UINT64                      ExtraRootBridgesLeft;
   UINTN                       LastRootBridgeNumber;
   UINTN                       RootBridgeNumber;
   PCI_HOST_BRIDGE_INSTANCE    *HostBridge;
@@ -236,6 +241,20 @@ InitializePciHostBridge (
     goto FreeHostBridge;
   }
 
+  //
+  // QEMU provides the number of extra root buses, shortening the exhaustive
+  // search below. If there is no hint, the feature is missing.
+  //
+  Status = QemuFwCfgFindFile ("etc/extra-pci-roots", &FwCfgItem, &FwCfgSize);
+  if (EFI_ERROR (Status) || FwCfgSize != sizeof ExtraRootBridgesLeft) {
+    ExtraRootBridgesLeft = 0;
+  } else {
+    QemuFwCfgSelectItem (FwCfgItem);
+    QemuFwCfgReadBytes (FwCfgSize, &ExtraRootBridgesLeft);
+    DEBUG ((EFI_D_INFO, "%a: %Lu extra root buses reported by QEMU\n",
+      __FUNCTION__, ExtraRootBridgesLeft));
+  }
+
   //
   // The "main" root bus is always there.
   //
@@ -247,7 +266,7 @@ InitializePciHostBridge (
   // alive.
   //
   for (RootBridgeNumber = 1;
-       RootBridgeNumber < 256;
+       RootBridgeNumber < 256 && ExtraRootBridgesLeft > 0;
        ++RootBridgeNumber) {
     UINTN Device;
 
@@ -271,6 +290,7 @@ InitializePciHostBridge (
       }
       InsertTailList (&HostBridge->Head, &RootBus->Link);
       LastRootBridgeNumber = RootBridgeNumber;
+      --ExtraRootBridgesLeft;
     }
   }
 
diff --git a/OvmfPkg/PciHostBridgeDxe/PciHostBridgeDxe.inf b/OvmfPkg/PciHostBridgeDxe/PciHostBridgeDxe.inf
index 40f4c3cc34..ca760b5497 100644
--- a/OvmfPkg/PciHostBridgeDxe/PciHostBridgeDxe.inf
+++ b/OvmfPkg/PciHostBridgeDxe/PciHostBridgeDxe.inf
@@ -26,6 +26,7 @@
 
 [Packages]
   MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
 
 [LibraryClasses]
   UefiDriverEntryPoint
@@ -39,6 +40,7 @@
   DevicePathLib
   IoLib
   PciLib
+  QemuFwCfgLib
 
 [Sources]
   PciHostBridge.c
-- 
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