tpm-be: report error instead of front-end

Backend can give more accurate error description, and lift out the job
from the frontend.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>

backends/tpm.c

@@ -54,9 +54,10 @@ enum TpmType tpm_backend_get_type(TPMBackend *s)
     return k->type;
 }
 
-int tpm_backend_init(TPMBackend *s, TPMIf *tpmif)
+int tpm_backend_init(TPMBackend *s, TPMIf *tpmif, Error **errp)
 {
     if (s->tpmif) {
+        error_setg(errp, "TPM backend '%s' is already initialized", s->id);
         return -1;
     }
 

hw/tpm/tpm_tis.c

@@ -1074,9 +1074,7 @@ static void tpm_tis_realizefn(DeviceState *dev, Error **errp)
 
     s->be_driver->fe_model = TPM_MODEL_TPM_TIS;
 
-    if (tpm_backend_init(s->be_driver, TPM_IF(s))) {
-        error_setg(errp, "tpm_tis: backend driver with id %s could not be "
-                   "initialized", s->backend);
+    if (tpm_backend_init(s->be_driver, TPM_IF(s), errp)) {
         return;
     }
 

include/sysemu/tpm_backend.h

@@ -99,12 +99,13 @@ enum TpmType tpm_backend_get_type(TPMBackend *s);
  * @s: the backend to initialized
  * @tpmif: TPM interface
  * @datacb: callback for sending data to frontend
+ * @errp: a pointer to return the #Error object if an error occurs.
  *
  * Initialize the backend with the given variables.
  *
  * Returns 0 on success.
  */
-int tpm_backend_init(TPMBackend *s, TPMIf *tpmif);
+int tpm_backend_init(TPMBackend *s, TPMIf *tpmif, Error **errp);
 
 /**
  * tpm_backend_startup_tpm: