[PATCH] MdeModulePkg/PciBusDxe: Enable Bus Master on P2P bridges on demand

[Ruiyu Ni <ruiyu.ni@intel.com>]

From: Ruiyu Ni <ruiyu.ni@microsoft.com>

The patch dynamically enables Bus Master on P2P bridges only
when requested by a device driver through PciIo.Attribute() to enable
the Bus Master.

Signed-off-by: Sean Brogan <sean.brogan@microsoft.com>
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c     | 16 +++++++++++++---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c | 18 +++++++++++++++---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c                |  8 ++++----
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c
index c0227fa2b6..359b9ded6d 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciDeviceSupport.c
@@ -1,7 +1,7 @@
 /** @file
   Supporting functions implementaion for PCI devices management.
 
-Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, 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
@@ -711,7 +711,12 @@ StartPciDevicesOnBridge (
                              0,
                              &Supports
                              );
-        Supports &= (UINT64)EFI_PCI_DEVICE_ENABLE;
+        //
+        // By default every bridge's IO and MMIO spaces are enabled.
+        // Bridge's Bus Master will be enabled when any device behind it requests
+        // to enable Bus Master.
+        //
+        Supports &= (UINT64) (EFI_PCI_IO_ATTRIBUTE_IO | EFI_PCI_IO_ATTRIBUTE_MEMORY);
         PciIoDevice->PciIo.Attributes (
                              &(PciIoDevice->PciIo),
                              EfiPciIoAttributeOperationEnable,
@@ -763,7 +768,12 @@ StartPciDevicesOnBridge (
                              0,
                              &Supports
                              );
-        Supports &= (UINT64)EFI_PCI_DEVICE_ENABLE;
+        //
+        // By default every bridge's IO and MMIO spaces are enabled.
+        // Bridge's Bus Master will be enabled when any device behind it requests
+        // to enable Bus Master.
+        //
+        Supports &= (UINT64) (EFI_PCI_IO_ATTRIBUTE_IO | EFI_PCI_IO_ATTRIBUTE_MEMORY);
         PciIoDevice->PciIo.Attributes (
                              &(PciIoDevice->PciIo),
                              EfiPciIoAttributeOperationEnable,
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
index 81171c82d9..f73756a31e 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
@@ -1218,11 +1218,12 @@ DetermineDeviceAttribute (
       return Status;
     }
     //
-    // Assume the PCI Root Bridge supports DAC
+    // Assume the PCI Root Bridge supports DAC and Bus Master.
     //
     PciIoDevice->Supports |= (UINT64)(EFI_PCI_IO_ATTRIBUTE_EMBEDDED_DEVICE |
                               EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM |
-                              EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE);
+                              EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE |
+                              EFI_PCI_IO_ATTRIBUTE_BUS_MASTER);
 
   } else {
 
@@ -1233,9 +1234,16 @@ DetermineDeviceAttribute (
     //
     Command = EFI_PCI_COMMAND_IO_SPACE     |
               EFI_PCI_COMMAND_MEMORY_SPACE |
-              EFI_PCI_COMMAND_BUS_MASTER   |
               EFI_PCI_COMMAND_VGA_PALETTE_SNOOP;
 
+    //
+    // Per PCI-to-PCI Bridge Architecture all PCI-to-PCI bridges are Bus Master capable.
+    // So only test the Bus Master capability for PCI devices.
+    //
+    if (!IS_PCI_BRIDGE(&PciIoDevice->Pci)) {
+      Command |= EFI_PCI_COMMAND_BUS_MASTER;
+    }
+
     BridgeControl = EFI_PCI_BRIDGE_CONTROL_ISA | EFI_PCI_BRIDGE_CONTROL_VGA | EFI_PCI_BRIDGE_CONTROL_VGA_16;
 
     //
@@ -1245,7 +1253,11 @@ DetermineDeviceAttribute (
 
     //
     // Set the supported attributes for specified PCI device
+    // Per PCI-to-PCI Bridge Architecture all PCI-to-PCI bridges are Bus Master capable.
     //
+    if (IS_PCI_BRIDGE(&PciIoDevice->Pci)) {
+      Command |= EFI_PCI_COMMAND_BUS_MASTER;
+    }
     PciSetDeviceAttribute (PciIoDevice, Command, BridgeControl, EFI_SET_SUPPORTS);
 
     //
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c
index cc7125e4fc..659f480d71 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c
@@ -1348,7 +1348,8 @@ ModifyRootBridgeAttributes (
   //
   Attributes &= ~(UINT64)(EFI_PCI_IO_ATTRIBUTE_EMBEDDED_DEVICE |
                           EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM |
-                          EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE);
+                          EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE |
+                          EFI_PCI_IO_ATTRIBUTE_BUS_MASTER);
 
   //
   // Record the new attribute of the Root Bridge
@@ -1726,12 +1727,11 @@ PciIoAttributes (
   }
   //
   // The upstream bridge should be also set to revelant attribute
-  // expect for IO, Mem and BusMaster
+  // expect for IO and Mem
   //
   UpStreamAttributes = Attributes &
                        (~(EFI_PCI_IO_ATTRIBUTE_IO     |
-                          EFI_PCI_IO_ATTRIBUTE_MEMORY |
-                          EFI_PCI_IO_ATTRIBUTE_BUS_MASTER
+                          EFI_PCI_IO_ATTRIBUTE_MEMORY
                           )
                         );
   UpStreamBridge = PciIoDevice->Parent;
-- 
2.12.2.windows.2