[SeaBIOS] Seabios Xen TPM check

[Jason Andryuk]

Hi,

SeaBIOS commit 67643955c746 (make SeaBios compatible with Xen vTPM.)
made tpm_start() exit before calling tpm_startup().  The commit
message has no explanation why this change was made.  Does anyone
remember why it was made?

The code today means SeaBIOS will not populate PCRs when running on
Xen.  If I revert the patch, SeaBIOS populates PCRs as one would
expect.  This is with a QEMU-emulated TPM backed by swtpm in TPM 1.2
mode (qemu & swtpm running in a linux stubdom).

Any insight is appreciated.

Thanks,
Jason