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

[Kevin O'Connor]

On Mon, Aug 12, 2013 at 08:05:08AM +0200, Gerd Hoffmann wrote:
> We'll need some way to make sure the pmbase (also mmconf xbar) set by
> the firmware matches the pmbase address filled into the acpi tables by
> qemu ...
> 
> So the options we have are:
> 
>   (1) Hardcode the address everywhere.  This is pretty close to the
>       current state, 0xb000 is hard-coded pretty much everywhere,
>       basically because older qemu versions had the pmbase register
>       readonly with 0xb000.  I'd like to move the pmbase somewhere else
>       long-term, to free the 0xb000-0xbfff window, so I'd like to avoid
>       that.
> 
>   (2) Have qemu pick pmbase/xbar addr.  Doesn't work due to
>       initialization order issues (especially xbar for coreboot).
> 
>   (3) Have firmware pick pmbase/xbar, have fixup instructions for the
>       addresses in in the loader script, simliar to the fixup
>       instructions for table-to-table pointers.
> 
>   (4) [ new idea by mst ]  Have firmware pick pmbase/xbar, then have
>       qemu look at the hardware registers programmed by the firmware,
>       use pmbase/xbar addresses found there there when generating the
>       tables.

I don't much like option 3 or 4.

Although hardcoding (option 1) is ugly, I think that ugliness does not
justify the complexity of run-time patching (3/4).

As for option 2 - I don't see why coreboot couldn't read the values
out of fw_cfg early on for the handful of cases like this.

-Kevin