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    [PATCH] arm: allow for arch-specific IOREMAP_MAX_ORDER · fd195c49
    Deepak Saxena 提交于
    Version 6 of the ARM architecture introduces the concept of 16MB pages
    (supersections) and 36-bit (40-bit actually, but nobody uses this) physical
    addresses.  36-bit addressed memory and I/O and ARMv6 can only be mapped
    using supersections and the requirement on these is that both virtual and
    physical addresses be 16MB aligned.  In trying to add support for ioremap()
    of 36-bit I/O, we run into the issue that get_vm_area() allows for a
    maximum of 512K alignment via the IOREMAP_MAX_ORDER constant.  To work
    around this, we can:
    
    - Allocate a larger VM area than needed (size + (1ul << IOREMAP_MAX_ORDER))
      and then align the pointer ourselves, but this ends up with 512K of
      wasted VM per ioremap().
    
    - Provide a new __get_vm_area_aligned() API and make __get_vm_area() sit
      on top of this. I did this and it works but I don't like the idea
      adding another VM API just for this one case.
    
    - My preferred solution which is to allow the architecture to override
      the IOREMAP_MAX_ORDER constant with it's own version.
    Signed-off-by: NDeepak Saxena <dsaxena@plexity.net>
    Cc: Russell King <rmk@arm.linux.org.uk>
    Signed-off-by: NAndrew Morton <akpm@osdl.org>
    Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
    fd195c49
vmalloc.c 13.0 KB