From: Ron Mercer <redacted>
Date: Tue, 30 Dec 2008 13:12:23 -0800

Shadow registers are consistent memory locations to which the chip
echos ring indexes in little endian format.  These values need to
be endian swapped before referencing.

Note:
The register pointer declaration uses the volatile modifier which
causes warnings in checkpatch.
Per Documentation/volatile-considered-harmful.txt:
  - Pointers to data structures in coherent memory which might be modified
    by I/O devices can, sometimes, legitimately be volatile.  A ring buffer
    used by a network adapter, where that adapter changes pointers to
    indicate which descriptors have been processed, is an example of this
    type of situation.

Signed-off-by: Ron Mercer <redacted>

Applied, but still kill the volatile and use proper memory
barriers around accesses to this value instead.

Many other drivers handle exactly this situation without
having to resort to volatile.