Re: [PATCH] MdeModulePkg/PciBus: Use actual max bus # for subordinary bus #

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

The code comment "// Get next available PCI bus number" comes from PciAllocateBusNumber?
It should be updated accordingly for PciGetMaxBusNumber, right?

With the comment updated, Reviewed-by: Star Zeng <star.zeng@intel.com>.


Thanks,
Star
-----Original Message-----
From: Ni, Ruiyu 
Sent: Wednesday, May 23, 2018 11:30 AM
To: edk2-devel@lists.01.org
Cc: Zeng, Star <star.zeng@intel.com>
Subject: [PATCH] MdeModulePkg/PciBus: Use actual max bus # for subordinary bus #

Current code assumes the max bus(0xFF) is under this P2P bridge and temporarily set it as subordinate bus.
It may cause silicon hangs during PCI enumeration in some specific case.

Instead, it should get the max bus number from the bus number resources returned from
PCI_HOST_BRIDGE_RESOURCE_ALLOCATION.StartBusEnumeration() and set it as subordinate bus.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c | 39 ++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
index 976496379a..729e86b55e 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
@@ -29,6 +29,43 @@ CHAR16 *mBarTypeStr[] = {
   L"Unknow"
   };
 
+/**
+  Retrieve the max bus number that is assigned to the Root Bridge hierarchy.
+  It can support the case that there are multiple bus ranges.
+
+  @param  Bridge           Bridge device instance.
+
+  @retval                  The max bus number that is assigned to this Root Bridge hierarchy.
+
+**/
+UINT16
+PciGetMaxBusNumber (
+  IN PCI_IO_DEVICE                      *Bridge
+  )
+{
+  PCI_IO_DEVICE                      *RootBridge;
+  EFI_ACPI_ADDRESS_SPACE_DESCRIPTOR  *BusNumberRanges;
+  UINT64                             MaxNumberInRange;
+
+  //
+  // Get PCI Root Bridge device
+  //
+  RootBridge = Bridge;
+  while (RootBridge->Parent != NULL) {
+    RootBridge = RootBridge->Parent;
+  }
+  MaxNumberInRange = 0;
+  //
+  // Get next available PCI bus number
+  //
+  BusNumberRanges = RootBridge->BusNumberRanges;
+  while (BusNumberRanges->Desc != ACPI_END_TAG_DESCRIPTOR) {
+    MaxNumberInRange = BusNumberRanges->AddrRangeMin + BusNumberRanges->AddrLen - 1;
+    BusNumberRanges++;
+  }
+  return (UINT16) MaxNumberInRange;
+}
+
 /**
   Retrieve the PCI Card device BAR information via PciIo interface.
 
@@ -1193,7 +1230,7 @@ PciScanBus (
           // Temporarily initialize SubBusNumber to maximum bus number to ensure the
           // PCI configuration transaction to go through any PPB
           //
-          Register  = 0xFF;
+          Register  = PciGetMaxBusNumber (Bridge);
           Address   = EFI_PCI_ADDRESS (StartBusNumber, Device, Func, PCI_BRIDGE_SUBORDINATE_BUS_REGISTER_OFFSET);
           Status = PciRootBridgeIo->Pci.Write (
                                           PciRootBridgeIo,
--
2.16.1.windows.1