[SeaBIOS] Long delay: WARNING - Timeout at wait_reg8:81!

[Kevin O'Connor]

On Mon, Mar 12, 2018 at 01:38:52PM -0400, Stephen Douthit wrote:
> I've got a board modded so I can jumper the TPM in and out.
> 
> What I found in the no-TPM case was that both tis_probe() and
> crb_probe() incorrectly return 1 for device present if all Fs are read.
> 
> For tis_probe() that was because rc wasn't updated to 0 if didvid was
> 0xffffffff.  For crb_probe() the last three return statements are
> inverted from what they should be, and the first 64bit address check
> returned the wrong value.  Fixing both probe functions got rid of the
> timeout for me when the TPM was disconnected.
> 
> It looks like there's a bit in the ACCESS register called Seize that
> must always read '0' for the version 1.2/1.3 interfaces.  I'd like to
> check that instead of didvid in tis_probe to handle the aborted read all
> 0s/Fs case.
> 
> I'd like to add a poll for tpmRegValidSts to crb_probe() similar to
> what's in tis_probe() to avoid potential races on real hardware.
> There's a Seize bit in TPM_LOC_CTRL_x which always reads 0 that we could
> use as a sanity check against the no device all Fs case.
> 
> Let me know if that sounds like a better way to catch the no device
> case, or if there's is some other check that would be better.

Thanks for looking at this.  It is common on x86 for invalid memory
accesses to return 0xff.  I don't know enough about the TPM hardware
to make a judgement call on the best way to test for presence.  I'd
like to hear what Stefan's thoughts are on this.

-Kevin