diff --git a/backends/tpm.c b/backends/tpm.c
index cf5abf1..c409a46 100644
--- a/backends/tpm.c
+++ b/backends/tpm.c
@@ -44,13 +44,6 @@ enum TpmType tpm_backend_get_type(TPMBackend *s)
     return k->ops->type;
 }
 
-const char *tpm_backend_get_desc(TPMBackend *s)
-{
-    TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
-
-    return k->ops->desc();
-}
-
 int tpm_backend_init(TPMBackend *s, TPMState *state,
                      TPMRecvDataCB *datacb)
 {
@@ -59,7 +52,7 @@ int tpm_backend_init(TPMBackend *s, TPMState *state,
     s->tpm_state = state;
     s->recv_data_callback = datacb;
 
-    return k->ops->init(s);
+    return k->ops->init ? k->ops->init(s) : 0;
 }
 
 int tpm_backend_startup_tpm(TPMBackend *s)
@@ -73,13 +66,15 @@ int tpm_backend_startup_tpm(TPMBackend *s)
                                        NULL);
     g_thread_pool_push(s->thread_pool, (gpointer)TPM_BACKEND_CMD_INIT, NULL);
 
-    return k->ops->startup_tpm(s);
+    return k->ops->startup_tpm ? k->ops->startup_tpm(s) : 0;
 }
 
 bool tpm_backend_had_startup_error(TPMBackend *s)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
+    assert(k->ops->had_startup_error);
+
     return k->ops->had_startup_error(s);
 }
 
@@ -87,6 +82,8 @@ size_t tpm_backend_realloc_buffer(TPMBackend *s, TPMSizedBuffer *sb)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
+    assert(k->ops->realloc_buffer);
+
     return k->ops->realloc_buffer(sb);
 }
 
@@ -100,7 +97,9 @@ void tpm_backend_reset(TPMBackend *s)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
-    k->ops->reset(s);
+    if (k->ops->reset) {
+        k->ops->reset(s);
+    }
 
     tpm_backend_thread_end(s);
 }
@@ -109,6 +108,8 @@ void tpm_backend_cancel_cmd(TPMBackend *s)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
+    assert(k->ops->cancel_cmd);
+
     k->ops->cancel_cmd(s);
 }
 
@@ -116,20 +117,24 @@ bool tpm_backend_get_tpm_established_flag(TPMBackend *s)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
-    return k->ops->get_tpm_established_flag(s);
+    return k->ops->get_tpm_established_flag ?
+           k->ops->get_tpm_established_flag(s) : false;
 }
 
 int tpm_backend_reset_tpm_established_flag(TPMBackend *s, uint8_t locty)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
-    return k->ops->reset_tpm_established_flag(s, locty);
+    return k->ops->reset_tpm_established_flag ?
+           k->ops->reset_tpm_established_flag(s, locty) : 0;
 }
 
 TPMVersion tpm_backend_get_tpm_version(TPMBackend *s)
 {
     TPMBackendClass *k = TPM_BACKEND_GET_CLASS(s);
 
+    assert(k->ops->get_tpm_version);
+
     return k->ops->get_tpm_version(s);
 }
 
diff --git a/hw/tpm/tpm_passthrough.c b/hw/tpm/tpm_passthrough.c
index 815a72e..a0459a6 100644
--- a/hw/tpm/tpm_passthrough.c
+++ b/hw/tpm/tpm_passthrough.c
@@ -227,15 +227,6 @@ static void tpm_passthrough_handle_request(TPMBackend *tb, TPMBackendCmd cmd)
     }
 }
 
-/*
- * Start the TPM (thread). If it had been started before, then terminate
- * and start it again.
- */
-static int tpm_passthrough_startup_tpm(TPMBackend *tb)
-{
-    return 0;
-}
-
 static void tpm_passthrough_reset(TPMBackend *tb)
 {
     TPMPassthruState *tpm_pt = TPM_PASSTHROUGH(tb);
@@ -247,11 +238,6 @@ static void tpm_passthrough_reset(TPMBackend *tb)
     tpm_pt->had_startup_error = false;
 }
 
-static int tpm_passthrough_init(TPMBackend *tb)
-{
-    return 0;
-}
-
 static bool tpm_passthrough_get_tpm_established_flag(TPMBackend *tb)
 {
     return false;
@@ -309,11 +295,6 @@ static void tpm_passthrough_cancel_cmd(TPMBackend *tb)
     }
 }
 
-static const char *tpm_passthrough_create_desc(void)
-{
-    return "Passthrough TPM backend driver";
-}
-
 static TPMVersion tpm_passthrough_get_tpm_version(TPMBackend *tb)
 {
     TPMPassthruState *tpm_pt = TPM_PASSTHROUGH(tb);
@@ -453,10 +434,8 @@ static const QemuOptDesc tpm_passthrough_cmdline_opts[] = {
 static const TPMDriverOps tpm_passthrough_driver = {
     .type                     = TPM_TYPE_PASSTHROUGH,
     .opts                     = tpm_passthrough_cmdline_opts,
-    .desc                     = tpm_passthrough_create_desc,
+    .desc                     = "Passthrough TPM backend driver",
     .create                   = tpm_passthrough_create,
-    .init                     = tpm_passthrough_init,
-    .startup_tpm              = tpm_passthrough_startup_tpm,
     .realloc_buffer           = tpm_passthrough_realloc_buffer,
     .reset                    = tpm_passthrough_reset,
     .had_startup_error        = tpm_passthrough_get_startup_error,
diff --git a/include/sysemu/tpm_backend.h b/include/sysemu/tpm_backend.h
index 202ec8d..13311cf 100644
--- a/include/sysemu/tpm_backend.h
+++ b/include/sysemu/tpm_backend.h
@@ -75,7 +75,7 @@ struct TPMDriverOps {
     enum TpmType type;
     const QemuOptDesc *opts;
     /* get a descriptive text of the backend to display to the user */
-    const char *(*desc)(void);
+    const char *desc;
 
     TPMBackend *(*create)(QemuOpts *opts, const char *id);
 
@@ -109,14 +109,6 @@ struct TPMDriverOps {
 enum TpmType tpm_backend_get_type(TPMBackend *s);
 
 /**
- * tpm_backend_get_desc:
- * @s: the backend
- *
- * Returns a human readable description of the backend.
- */
-const char *tpm_backend_get_desc(TPMBackend *s);
-
-/**
  * tpm_backend_init:
  * @s: the backend to initialized
  * @state: TPMState
diff --git a/tpm.c b/tpm.c
index b19b1a3..db14849 100644
--- a/tpm.c
+++ b/tpm.c
@@ -62,7 +62,7 @@ static void tpm_display_backend_drivers(void)
             continue;
         }
         fprintf(stderr, "%12s   %s\n",
-                TpmType_str(i), be_drivers[i]->desc());
+                TpmType_str(i), be_drivers[i]->desc);
     }
     fprintf(stderr, "\n");
 }
