Re: [edk2-devel] [PATCH for-edk2-stable201905 3/6] Revert "OvmfPkg/PlatformPei: hoist PciBase assignment above the i440fx/q35 branching"

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 5/29/19 5:12 PM, Laszlo Ersek wrote:
> This reverts commit 9a2e8d7c65ef7f39c6754d27e52954b616bc6628.
> 
> The original fix for <https://bugzilla.tianocore.org/show_bug.cgi?id=1814>
> triggered a bug / incorrect assumption in QEMU.
> 
> QEMU assumes that the PCIEXBAR is below the 32-bit PCI window, not above
> it. When the firmware doesn't satisfy this assumption, QEMU generates an
> \_SB.PCI0._CRS object in the ACPI DSDT that does not reflect the
> firmware's 32-bit MMIO BAR assignments. This causes OSes to re-assign
> 32-bit MMIO BARs.
> 
> Working around the problem in the firmware looks less problematic than
> fixing QEMU. Revert the original changes first, before implementing an
> alternative fix.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1859
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>

> ---
>  OvmfPkg/PlatformPei/Platform.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
> index 9c013613a1a0..5e0a15484230 100644
> --- a/OvmfPkg/PlatformPei/Platform.c
> +++ b/OvmfPkg/PlatformPei/Platform.c
> @@ -181,7 +181,6 @@ MemMapInitialization (
>  
>      TopOfLowRam = GetSystemMemorySizeBelow4gb ();
>      PciExBarBase = 0;
> -    PciBase = (TopOfLowRam < BASE_2GB) ? BASE_2GB : TopOfLowRam;
>      if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
>        //
>        // The MMCONFIG area is expected to fall between the top of low RAM and
> @@ -193,6 +192,7 @@ MemMapInitialization (
>        PciBase = (UINT32)(PciExBarBase + SIZE_256MB);
>        PciSize = 0xFC000000 - PciBase;
>      } else {
> +      PciBase = (TopOfLowRam < BASE_2GB) ? BASE_2GB : TopOfLowRam;
>        PciSize = 0xFC000000 - PciBase;
>      }
>  
>