Re: [PATCH RESEND 3/3] OvmfPkg/XenSupport: turn off address decoding before BAR sizing

[Igor Druzhinin <igor.druzhinin@citrix.com>]

On 14/03/2019 17:55, Anthony PERARD wrote:
> On Wed, Mar 06, 2019 at 12:40:56PM +0000, Igor Druzhinin wrote:
>> 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@citrix.com>
>> ---
>>  OvmfPkg/Library/PciHostBridgeLib/XenSupport.c | 34 +++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>>
>> diff --git a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
>> index 408fb24..9940335 100644
>> --- a/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
>> +++ b/OvmfPkg/Library/PciHostBridgeLib/XenSupport.c
>> @@ -55,6 +55,33 @@ PcatPciRootBridgeBarExisted (
>>    EnableInterrupts ();
>>  }
>>  
>> +#define EFI_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 & EFI_PCI_COMMAND_DECODE)
>> +       PciWrite16 (Address, *OriginalValue & ~EFI_PCI_COMMAND_DECODE);
> 
> The edk2 coding style ask to always use { } with if:
> https://github.com/tianocore/tianocore.github.io/wiki/Code-Style-C
> 
>> +  } else {
>> +    if (Value & EFI_PCI_COMMAND_DECODE)
>> +      PciWrite16 (Address, Value);
> 
> here too.
> 
>> +  }
>> +}
>> +
>>  STATIC
>>  VOID
>>  PcatPciRootBridgeParseBars (
>> @@ -76,6 +103,7 @@ PcatPciRootBridgeParseBars (
>>    UINT32                            Value;
>>    UINT32                            OriginalUpperValue;
>>    UINT32                            UpperValue;
>> +  UINT16                            OriginalCommand;
>>    UINT64                            Mask;
>>    UINTN                             Offset;
>>    UINT64                            Base;
>> @@ -83,6 +111,12 @@ 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, &OriginalCommand
> 
> Is it on purpose that the original register value is stored in
> OriginalCommand, but never used again?

Those are probably remnants of extended patch version for XenServer -
will remove together with other suggestions from you and Laszlo.

Igor