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

[Anthony PERARD <anthony.perard@citrix.com>]

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?

> +  );
> +
>    for (Offset = BarOffsetBase; Offset < BarOffsetEnd; Offset += sizeof (UINT32)) {
>      PcatPciRootBridgeBarExisted (
>        PCI_LIB_ADDRESS (Bus, Device, Function, Offset),

Thanks,

-- 
Anthony PERARD