Re: [Qemu-devel] [SeaBIOS] [PATCH] acpi: hide 64-bit PCI hole for Windows XP

[Gerd Hoffmann]

On 08/08/13 10:37, Michael S. Tsirkin wrote:
> On Thu, Aug 08, 2013 at 09:57:39AM +0200, Gerd Hoffmann wrote:
>>>>   (3) mmconf xbar start (MCFG, q35 only, at 0xb0000000 now).
>>>>   (4) pmbase (FADT, at 0xb000 now).
>>>>
>>>> Especially 3+4 tend to be compile-time constants in the firmware as they
>>>> are needed very early in the setup process.
>>>
>>> So we don't need them in pci-config, just stick constant in ACPI.
>>
>> I don't want them be constant.  I want allow the firmware pick them.
>> Our mmconfig xbar is 256M and can handle 256 busses.  I'd like to have
>> the option to reduce that to 64M and place it somewhere else.
>>
>> Also coreboot and seabios use different values for pmbase.  coreboot on
>> q35 maps the pmbase below 0x1000.  Which surely makes sense.  When we
>> don't place chipset stuff at 0xb000 we can assign the 0xb000->0xbfff
>> window to a pci bridge instead.
> 
> Yes, this might be useful. But I don't think it's required to
> use linker to patch ACPI tables for this - we can write ASL code to read
> the register back from device configuration, instead.

No, we can't, because the address is in the FADT.

cheers,
  Gerd