+ struct dz_mux *mux = to_dport(uport)->mux;
+ int map_guard;
+ int ret;
+
+ map_guard = atomic_add_return(1, &mux->map_guard);
+ if (map_guard == 1) {
+ if (!request_mem_region(uport->mapbase, dec_kn_slot_size,
+ "dz")) {
+ atomic_add(-1, &mux->map_guard);
+ printk(KERN_ERR
+ "dz: Unable to reserve MMIO resource\n");
+ return -EBUSY;
+ }
+ }
+ ret = dz_map_port(uport);
+ if (ret) {
+ map_guard = atomic_add_return(-1, &mux->map_guard);
+ if (!map_guard)
+ release_mem_region(uport->mapbase, dec_kn_slot_size);
+ return ret;
+ }