1. 26 Sep, 2008 7 commits
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  4. 06 Sep, 2008 1 commit
    • Lennert Buytenhek's avatar
      [ARM] 5241/1: provide ioremap_wc() · 1ad77a87
      Lennert Buytenhek authored
      
      
      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: default avatarLennert Buytenhek <buytenh@marvell.com>
      Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      1ad77a87
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