• Linus Torvalds's avatar
    fsldma: fix very broken 32-bit ppc ioread64 functionality · 0a4c56c8
    Linus Torvalds authored
    Commit ef91bb19 ("kernel.h: Silence sparse warning in
    lower_32_bits") caused new warnings to show in the fsldma driver, but
    that commit was not to blame: it only exposed some very incorrect code
    that tried to take the low 32 bits of an address.
    That made no sense for multiple reasons, the most notable one being that
    that code was intentionally limited to only 32-bit ppc builds, so "only
    low 32 bits of an address" was completely nonsensical.  There were no
    high bits to mask off to begin with.
    But even more importantly fropm a correctness standpoint, turning the
    address into an integer then caused the subsequent address arithmetic to
    be completely wrong too, and the "+1" actually incremented the address
    by one, rather than by four.
    Which again was incorrect, since the code was reading two 32-bit values
    and trying to make a 64-bit end result of it all.  Surprisingly, the
    iowrite64() did not suffer from the same odd and incorrect model.
    This code has never worked, but it's questionable whether anybody cared:
    of the two users that actually read the 64-bit value (by way of some C
    preprocessor hackery and eventually the 'get_cdar()' inline function),
    one of them explicitly ignored the value, and the other one might just
    happen to work despite the incorrect value being read.
    This patch at least makes it not fail the build any more, and makes the
    logic superficially sane.  Whether it makes any difference to the code
    _working_ or not shall remain a mystery.
    Compile-tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Reviewed-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
fsldma.h 7.91 KB