read or write date through flash

Yes, in 99% of cases using IORD and IOWR will be more obvious and just as fast.

The only case where it might be a good idea to use the bit31 method is where you are passing a pointer to another function (such as memcpy) which wouldn't otherwise understand that it is copying from uncacheable memory.

But note that you must never use the bit31 method for accesses to native bus aligned registers, as this might not work in future.