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    SubjectRe: [PATCH 3/3] x86: restore old GART alloc_coherent behavior
    On Wed, 24 Sep 2008 20:48:37 +0900
    FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:

    > Currently, GART alloc_coherent tries to allocate pages with GFP_DMA32
    > for a device having dma_masks > 24bit < 32bits. If GART gets an
    > address that a device can't access to, GART try to map the address to
    > a virtual I/O address that the device can access to.
    >
    > But Andi pointed out, "The GART is somewhere in the 4GB range so you
    > cannot use it to map anything < 4GB. Also GART is pretty small."
    >
    > http://lkml.org/lkml/2008/9/12/43
    >
    > That is, it's possible that GART doesn't have virtual I/O address
    > space that a device can access to. The above behavior doesn't work for
    > a device having dma_masks > 24bit < 32bits.
    >
    > This patch restores old GART alloc_coherent behavior (before the
    > alloc_coherent rewrite).
    >
    > Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

    Acked-by: Alan Cox <alan@redhat.com>

    This is indeed a specific problem found with things like older AACRAID
    where control blocks must be below 31bits and the GART is above 0x80000000

    Alan


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