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    SubjectRe: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver
    On Fri, 13 Jul 2007, James Bottomley wrote:
    > On Fri, 2007-07-13 at 15:25 +0200, Geert Uytterhoeven wrote:
    > > kmap() just returns page_address() on ppc64, as there's no highmem.
    > > kunmap() is a no-op.
    > > So technically I could just use page_address() directly, but Christoph
    > > wanted
    > > me to keep the kmap()/kunmap() sequence because it's considered a good
    > > practice.
    > The point isn't what kmap and kunmap do ... it's the addresses they
    > return. By and large, a kernel virtual address for a page is different
    > from the user virtual address. If the cache is virtually indexed you
    > get different cache lines for the same page ... and that sets you up
    > with aliases you need to resolve. parisc is the same ... our
    > kmap/kunmap are nops as well, but our kernel virtual addresses are still
    > different from the user virtual ones.


    - flush_kernel_dcache_page() is a no-op on ppc64
    (ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE is defined on parisc only).

    - For reference, drivers/scsi/ipr.c (another ppc64 driver) just uses a plain
    kmap/memcpy/kunmap sequence

    So what should I do?

    With kind regards,

    Geert Uytterhoeven
    Software Architect

    Sony Network and Software Technology Center Europe
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