Re: [Qemu-devel] [PATCH 0/5] Extend TPM support with a QEMU-external TPM

[Kevin O'Connor]

On Mon, May 04, 2015 at 11:22:25AM -0400, Stefan Berger wrote:
> On 05/04/2015 05:16 AM, Igor Mammedov wrote:
> >On Wed, 29 Apr 2015 12:42:21 -0400
> >>2 choices now -- which one to take?
> >I'd try installing extra SSDT table first as a cleanest way (seabios only)
> >and if it fails fallback to TIS path.
> 
> I did some experiment where I tried to use AML's Store() call to see whether
> it can read from some entry in another scope, similar to what the specs show
> on page 487, so that one could read the base address that is written
> elsewhere. The problem seems to be that there is no actual searching going
> on for accessing a scope during runtime, but this seems to be done during
> compile time. So something like Store(\_SB.I2C1.Y, BUFF) from the specs
> needs to have a SCOPE(\_SB.I2C1...) available during compile time.

You can reference scopes provided by other SSDTs/DSDT using the
"External()" acpi command.

> Otherwise I am not sure how to go about this. The only way I could think of
> would be to write a unique and 'recognizeable' address into the AML,
> something like 0x12345678, try to find it in SeaBIOS and replace it with the
> actual address. It doesn't seem right, tough. The next best choice would be
> to paravirtualize the TIS with bytes that survive a reset.

I don't think it's a good idea to have SeaBIOS modify the QEMU
provided ACPI tables.  It also shouldn't be necessary.  If there's
anything that QEMU needs in the guest memory, then QEMU should be able
to build it and tell SeaBIOS to allocate it via the existing
"romfile_loader" mechanism.

-Kevin