target/linux/mvebu/patches-3.18/030-do_not_register_custom_DMA_operations_when_coherency_is_disabled.patch

   1 This patch is a partial backport of commit ef01c6c36bb8 ("ARM: mvebu:
   2 remove Armada 375 Z1 workaround for I/O coherency"). This commit was
   3 merged in v3.19, so kernel versions later than v3.19 are not affected
   4 by the problem that this commit fixes.
   5
   6 It does not make a lot of sense to backport this commit entirely,
   7 since it is mainly removing some no longer useful code. However, this
   8 commit is also making sure that the bus_register_notifier that
   9 register the custom DMA operations that should be used for HW I/O
  10 coherency does not get registered when said HW I/O coherency is not
  11 enabled.
  12
  13 This is particularly critical since we have decided to disable HW I/O
  14 coherency completely in all kernels < 4.0, to be on the safe side,
  15 while experimenting a new implementation of the HW I/O coherency in >=
  16 4.0.
  17
  18 Without this commit, kernels earlier than 3.18 have the custom DMA
  19 operations normally used for HW I/O coherency registered (they don't
  20 do cache maintenance operations), while HW I/O coherency is
  21 disabled. It essentially causes every DMA transfer to transfer
  22 garbage.
  23
  24 The issue fixed by this commit was introduced by 5ab5afd8ba83 ("ARM:
  25 mvebu: implement Armada 375 coherency workaround"), but it was not
  26 visible until now since it didn't cause any problem when HW I/O
  27 coherency is enabled.
  28
  29 Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
  30 Cc: <stable@vger.kernel.org> v3.16..v3.18
  31 ---
  32  arch/arm/mach-mvebu/coherency.c | 5 +++--
  33  1 file changed, 3 insertions(+), 2 deletions(-)
  34
  35 --- a/arch/arm/mach-mvebu/coherency.c
  36 +++ b/arch/arm/mach-mvebu/coherency.c
  37 @@ -391,8 +391,9 @@ static int __init coherency_late_init(vo
  38                         armada_375_coherency_init_wa();
  39         }
  40
  41 -       bus_register_notifier(&platform_bus_type,
  42 -                             &mvebu_hwcc_nb);
  43 +       if (coherency_available())
  44 +               bus_register_notifier(&platform_bus_type,
  45 +                                     &mvebu_hwcc_nb);
  46
  47         return 0;
  48  }