tpm: ibmvtpm: Wait for ready buffer before probing for TPM2 attributes

The tpm2_get_cc_attrs_tbl() call will result in TPM commands being issued,
which will need the use of the internal command/response buffer.  But,
we're issuing this *before* we've waited to make sure that buffer is
allocated.

This can result in intermittent failures to probe if the hypervisor / TPM
implementation doesn't respond quickly enough.  I find it fails almost
every time with an 8 vcpu guest under KVM with software emulated TPM.

To fix it, just move the tpm2_get_cc_attrs_tlb() call after the
existing code to wait for initialization, which will ensure the buffer
is allocated.

Fixes: 18b3670d79 ("tpm: ibmvtpm: Add support for TPM2")
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

drivers/char/tpm/tpm_ibmvtpm.c

@@ -683,13 +683,6 @@ static int tpm_ibmvtpm_probe(struct vio_dev *vio_dev,
 	if (rc)
 		goto init_irq_cleanup;
 
-	if (!strcmp(id->compat, "IBM,vtpm20")) {
-		chip->flags |= TPM_CHIP_FLAG_TPM2;
-		rc = tpm2_get_cc_attrs_tbl(chip);
-		if (rc)
-			goto init_irq_cleanup;
-	}
-
 	if (!wait_event_timeout(ibmvtpm->crq_queue.wq,
 				ibmvtpm->rtce_buf != NULL,
 				HZ)) {
@@ -697,6 +690,13 @@ static int tpm_ibmvtpm_probe(struct vio_dev *vio_dev,
 		goto init_irq_cleanup;
 	}
 
+	if (!strcmp(id->compat, "IBM,vtpm20")) {
+		chip->flags |= TPM_CHIP_FLAG_TPM2;
+		rc = tpm2_get_cc_attrs_tbl(chip);
+		if (rc)
+			goto init_irq_cleanup;
+	}
+
 	return tpm_chip_register(chip);
 init_irq_cleanup:
 	do {