[Xen-devel] [PATCH v2 3/3] OvmfPkg/XenSupport: turn off address decoding before BAR sizing

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On Xen, hvmloader firmware leaves address decoding enabled for
enumerated PCI device before jumping into OVMF. OVMF seems to
expect it to be disabled and tries to size PCI BARs in several places
without disabling it which causes BAR64, for example, being
incorrectly placed by QEMU.

Fix it by disabling PCI address decoding explicitly before the
first attempt to size BARs on Xen.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
---
Changes in v2:
* coding style issues and minor suggestions
---
 OvmfPkg/Library/PciHostBridgeLib/XenSupport.c | 35 +++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c 
b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
index f763134..67a37cd 100644
--- a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
+++ b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
@@ -55,6 +55,35 @@ PcatPciRootBridgeBarExisted (
   EnableInterrupts ();
 }
 
+#define PCI_COMMAND_DECODE ((UINT16)(EFI_PCI_COMMAND_IO_SPACE | \
+                                     EFI_PCI_COMMAND_MEMORY_SPACE))
+STATIC
+VOID
+PcatPciRootBridgeDecoding (
+  IN  UINTN                          Address,
+  IN  BOOLEAN                        Enabled,
+  OUT UINT16                         *OriginalValue
+  )
+{
+  UINT16                             Value;
+
+  //
+  // Preserve the original value
+  //
+  Value = *OriginalValue;
+  *OriginalValue = PciRead16 (Address);
+
+  if (!Enabled) {
+    if (*OriginalValue & PCI_COMMAND_DECODE) {
+      PciWrite16 (Address, *OriginalValue & ~PCI_COMMAND_DECODE);
+    }
+  } else {
+    if (Value & PCI_COMMAND_DECODE) {
+      PciWrite16 (Address, Value);
+    }
+  }
+}
+
 STATIC
 VOID
 PcatPciRootBridgeParseBars (
@@ -81,6 +110,12 @@ PcatPciRootBridgeParseBars (
   UINT64                            Limit;
   PCI_ROOT_BRIDGE_APERTURE          *MemAperture;
 
+  // Disable address decoding for every device before OVMF starts sizing it
+  PcatPciRootBridgeDecoding (
+    PCI_LIB_ADDRESS (Bus, Device, Function, PCI_COMMAND_OFFSET),
+    FALSE, (UINT16 *)&OriginalValue
+  );
+
   for (Offset = BarOffsetBase; Offset < BarOffsetEnd; Offset += sizeof 
(UINT32)) {
     PcatPciRootBridgeBarExisted (
       PCI_LIB_ADDRESS (Bus, Device, Function, Offset),
-- 
2.7.4


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