30 Nov, 2008

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01 Oct, 2008

1 commit


06 Sep, 2008

1 commit

  • This patch provides an ARM implementation of ioremap_wc().

    We use different page table attributes depending on which CPU we
    are running on:

    - Non-XScale ARMv5 and earlier systems: The ARMv5 ARM documents four
    possible mapping types (CB=00/01/10/11). We can't use any of the
    cached memory types (CB=10/11), since that breaks coherency with
    peripheral devices. Both CB=00 and CB=01 are suitable for _wc, and
    CB=01 (Uncached/Buffered) allows the hardware more freedom than
    CB=00, so we'll use that.

    (The ARMv5 ARM seems to suggest that CB=01 is allowed to delay stores
    but isn't allowed to merge them, but there is no other mapping type
    we can use that allows the hardware to delay and merge stores, so
    we'll go with CB=01.)

    - XScale v1/v2 (ARMv5): same as the ARMv5 case above, with the slight
    difference that on these platforms, CB=01 actually _does_ allow
    merging stores. (If you want noncoalescing bufferable behavior
    on Xscale v1/v2, you need to use XCB=101.)

    - Xscale v3 (ARMv5) and ARMv6+: on these systems, we use TEXCB=00100
    mappings (Inner/Outer Uncacheable in xsc3 parlance, Uncached Normal
    in ARMv6 parlance).

    The ARMv6 ARM explicitly says that any accesses to Normal memory can
    be merged, which makes Normal memory more suitable for _wc mappings
    than Device or Strongly Ordered memory, as the latter two mapping
    types are guaranteed to maintain transaction number, size and order.
    We use the Uncached variety of Normal mappings for the same reason
    that we can't use C=1 mappings on ARMv5.

    The xsc3 Architecture Specification documents TEXCB=00100 as being
    Uncacheable and allowing coalescing of writes, which is also just
    what we need.

    Signed-off-by: Lennert Buytenhek
    Signed-off-by: Russell King

    Lennert Buytenhek
     

07 Aug, 2008

1 commit


03 Aug, 2008

1 commit