Re: [PATCH] tpm_tis: Hold locality open during probe

From: Jason Andryuk
Date: Tue Jul 12 2022 - 11:29:30 EST

On Mon, Jul 11, 2022 at 3:37 PM Jason Andryuk <jandryuk@xxxxxxxxx> wrote:
> On Sun, Jul 10, 2022 at 10:58 PM Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote:
> >
> > Can you test against
> >
> >
> I applied on top of 5.15.53, and the probe on boot still fails.
> Manually probing works intermittently.

On top of Lino Sanfilippo's patch queue, I added an additional
tpm_tis_request_locality and tpm_tis_release_locality to hold the
locality open via refcount in tpm_tis_chip_init. Similar to my patch
in this thread, it acquires the locality before the TPM_INT_ENABLE
write and holds it until after the TPM_RID read. That fixes the probe
issue on the box where I tested.

While tpm_tis_core_init is definitely a problem, I wonder if there are
other code paths that could trigger this acquire -> release ->
acquire issue. In that light, restoring a wait by reverting commit
e42acf104d6e ("tpm_tis: Clean up locality release") seems safer since
it would cover any code path. I just tested reverting that and it
still fails to probe on boot and intermittently. I'm surprised since
I expected it to solve the issue, but my original debugging was
showing TPM_ACCESS_ACTIVE_LOCALITY cleared (and never re-set) so the
driver isn't actually waiting.

All this locality acquiring and releasing seems rather redundant. If
locality 0 is all that is ever used, why not just hold it open? I
guess Trench Boot/Secure Launch wants to use locality 2
but in either case doesn't the system just stay in the assigned
locality? I haven't read the spec, so maybe that is disallowed.
There is something nice about cleaning up and releasing the locality
when not in use, but it's also causing a problem here.