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    SubjectRe: [PATCH] asm-generic: add a dma-mapping.h file
    Arnd Bergmann wrote:
    > h8300 and m32r currently do not provide a DMA mapping API
    > and therefore cannot use the ATA drivers. This adds a
    > generic version of dma-mapping.h for architectures that
    > have none or very minimal actual support for DMA in hardware
    > and makes the two architectures use it.
    >
    > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    > ---
    > On Sunday 17 May 2009 20:05:54 Jeff Garzik wrote:
    >
    >> That's what needs to happen. We provide no-op functions for e.g. PCI
    >> and x86 DMI, for platforms where this support does not exist.
    >>
    >> Pretty much all architectures support some form of ATA. m68k, m32r,
    >> h8300 and microblaze all have IDE interface, which means that libata
    >> needs to work on that platform.
    >>
    >> The only !ATA arch in the entire kernel is s390, AFAICT.
    >
    > m68k only defines NO_DMA for Sun3 and Dragonball. Sun3 does
    > not have ATA, Dragonball could probably just enable HAS_DMA.
    >
    > ---
    > arch/h8300/Kconfig | 2 +-
    > arch/h8300/include/asm/dma-mapping.h | 1 +
    > arch/m32r/Kconfig | 2 +-
    > arch/m32r/include/asm/dma-mapping.h | 1 +
    > include/asm-generic/dma-mapping.h | 399 ++++++++++++++++++++++++++++++++++
    > 5 files changed, 403 insertions(+), 2 deletions(-)
    > create mode 100644 arch/h8300/include/asm/dma-mapping.h
    > create mode 100644 arch/m32r/include/asm/dma-mapping.h
    > create mode 100644 include/asm-generic/dma-mapping.h

    My main comment is a bit non-specific... I tend to think that all
    no-dma platforms should provide an API whose implementation always
    returns errors, e.g. an inlined version of dma-mapping-broken.h.

    That sort of setup permits the compiler's dead code elimination to work
    on these no-dma platforms, while not crapping up the libata code with a
    bunch of ifdefs.

    Jeff






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