My Nuvoton 6xx in a Dell XPS-13 has been intermittently failing to work
(necessitating a reboot). The problem seems to be that the TPM gets into a
state where the partial self-test doesn't return TPM_RC_SUCCESS (meaning
all tests have run to completion), but instead returns TPM_RC_TESTING
(meaning some tests are still running in the background).  There are
various theories that resending the self-test command actually causes the
tests to restart and thus triggers more TPM_RC_TESTING returns until the
timeout is exceeded.

There are several issues here: firstly being we shouldn't slow down the
boot sequence waiting for the self test to complete once the TPM
backgrounds them.  It will actually make available all functions that have
passed and if it gets a failure return TPM_RC_FAILURE to every subsequent
command.  So the fix is to kick off self tests once and if they return
TPM_RC_TESTING log that as a backgrounded self test and continue on.  In
order to prevent other tpm users from seeing any TPM_RC_TESTING returns
(which it might if they send a command that needs a TPM subsystem which is
still under test), we loop in tpm_transmit_cmd until either a timeout or we
don't get a TPM_RC_TESTING return.

Finally, there have been observations of strange returns from a partial
test. One Nuvoton is occasionally returning TPM_RC_COMMAND_CODE, so treat
any unexpected return from a partial self test as an indication we need to
run a full self test.

[jarkko.sakkinen@linux.intel.com: cleaned up some klog messages and
 dropped tpm_transmit_check() helper function from James' original
 commit.]

Fixes: 2482b1bb

 ("tpm: Trigger only missing TPM 2.0 self tests")
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com>