return NULL;
 }
 
-static void dump_mb(struct cx18 *cx, struct cx18_mailbox *mb, char *name)
+/* Call with buf of n*11+1 bytes */
+static char *u32arr2hex(u32 data[], int n, char *buf)
 {
-       char argstr[MAX_MB_ARGUMENTS*11+1];
        char *p;
        int i;
 
+       for (i = 0, p = buf; i < n; i++, p += 11) {
+               /* kernel snprintf() appends '\0' always */
+               snprintf(p, 12, " %#010x", data[i]);
+       }
+       *p = '\0';
+       return buf;
+}
+
+static void dump_mb(struct cx18 *cx, struct cx18_mailbox *mb, char *name)
+{
+       char argstr[MAX_MB_ARGUMENTS*11+1];
+
        if (!(cx18_debug & CX18_DBGFLG_API))
                return;
 
-       for (i = 0, p = argstr; i < MAX_MB_ARGUMENTS; i++, p += 11) {
-               /* kernel snprintf() appends '\0' always */
-               snprintf(p, 12, " %#010x", mb->args[i]);
-       }
        CX18_DEBUG_API("%s: req %#010x ack %#010x cmd %#010x err %#010x args%s"
-               "\n", name, mb->request, mb->ack, mb->cmd, mb->error, argstr);
+                      "\n", name, mb->request, mb->ack, mb->cmd, mb->error,
+                      u32arr2hex(mb->args, MAX_MB_ARGUMENTS, argstr));
 }
 
 
                                "incoming %s to EPU mailbox (sequence no. %u)"
                                "\n",
                                rpu_str[rpu], rpu_str[rpu], order_mb->request);
-               dump_mb(cx, order_mb, "incoming");
+               if (cx18_debug & CX18_DBGFLG_WARN)
+                       dump_mb(cx, order_mb, "incoming");
                order->flags = CX18_F_EWO_MB_STALE_UPON_RECEIPT;
        }
 
        struct mutex *mb_lock;
        long int timeout, ret;
        int i;
+       char argstr[MAX_MB_ARGUMENTS*11+1];
 
        if (info == NULL) {
                CX18_WARN("unknown cmd %x\n", cmd);
                return -EINVAL;
        }
 
-       if (cmd == CX18_CPU_DE_SET_MDL)
-               CX18_DEBUG_HI_API("%s\n", info->name);
-       else
-               CX18_DEBUG_API("%s\n", info->name);
+       if (cx18_debug & CX18_DBGFLG_API) { /* only call u32arr2hex if needed */
+               if (cmd == CX18_CPU_DE_SET_MDL) {
+                       if (cx18_debug & CX18_DBGFLG_HIGHVOL)
+                               CX18_DEBUG_HI_API("%s\tcmd %#010x args%s\n",
+                                               info->name, cmd,
+                                               u32arr2hex(data, args, argstr));
+               } else
+                       CX18_DEBUG_API("%s\tcmd %#010x args%s\n",
+                                      info->name, cmd,
+                                      u32arr2hex(data, args, argstr));
+       }
 
        switch (info->rpu) {
        case APU: