#define MEMTX_OK 0
#define MEMTX_ERROR (1U << 0) /* device returned an error */
#define MEMTX_DECODE_ERROR (1U << 1) /* nothing at that address */
+#define MEMTX_BUS_ERROR (1U << 2) /* bus returned an error */
This is kind of odd naming, because MEMTX_DECODE_ERROR already means
"bus/interconnect returned an error" and it generally translates
into what at the OS level gets called a "bus error"...
MEMTX_DECODE_ERROR is "nothing at that address". We want a name
for "there is something, but you don't have access to it".
Maybe MEMTX_ILLEGAL_ERROR?