Re: [tpmdd-devel] tpm device not showing up in /dev anymore

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Sat, Nov 11, 2017 at 01:31:32PM -0700, Jerry Snitselaar wrote:
> On Sat Nov 11 17, Jason Gunthorpe wrote:
> > On Sat, Nov 11, 2017 at 12:12:57PM -0700, Jerry Snitselaar wrote:
> > 
> > > Before the release_locality code would only actually release the
> > > locality if the request use bit was set. So after it grabbed the
> > > locality during probe it probably never released it. The idea with the
> > > new code was to release it when it was no longer needed so another
> > > requester would be able to take the tpm without having to wait for it
> > > to be released.
> > 
> > If I recall, this was so that system level things outside linux could
> > access the TPM properly??
> > 
> 
> Yes, that is what drove this initially. I believe Jarkko was also
> thinking of the possibility in the future where something like a vm
> could request a locality as well, but that is just a hazy recollection
> of emails from back then.

This was something I recall discussing in LPC 2016 in the hallway at
least :-) A tidbit but it could make sense to tie it to VMM, not VM.

> 
> > > With the old code I think it would have to wait either
> > > until the next time release_locality was called, or attempt to seize
> > > the tpm with the seize bit in the access register. I need to read
> > > through the spec some more, but does the tpm ever force a change when
> > > the request use bit is set, or does it leave it up to the software
> > > to deal with it and only gets involved in the case where the seize
> > > bit has been set?
> > 
> > Do we handle these cases? Maybe something like that has happened..
> > 
> > Jason
> 
> If that is what happened in this case we should see the beenSeized bit
> set in the access register (assuming the chip is doing things properly),
> but it only had the tpmRegValidSts and tpmEstablishment bits set.
> 
> There is code in the interrupt handling that notices if the locality
> changes if the chip has that capability, but I don't think there is
> anything that deals with the seize bit. Another thing to be looked
> at.

For me it is hard to understand who is the 3rd party who would be using
other locality and accessing TPM after OS handover in the regression in
question.

/Jarkko