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    SubjectRe: [PATCH] drivers/ata: Add the SW NCQ support to sata_nv for MCP51/MCP55/MCP61
    On Fri, 18 May 2007 10:34:35 -0400
    Jeff Garzik <> wrote:

    > Alan Cox wrote:
    > >> That shouldn't be a problem, libata default DMA mask is 32 bits (which
    > >> isn't overridden with this controller) and so the block layer will
    > >> bounce any data being read/written above that point with IOMMU or
    > >> swiotlb. The comment is a bit unnecessarily scary.
    > >
    > > Adding a BUG_ON for this would be wise. Its trivial to check and a BUG
    > > rather than corruption if this assumption ever changes would be far
    > > preferable
    > The default DMA mask -everywhere- is 32 bits.
    > A lot of code will break if this assumption ever changes, not just libata.

    Little lesson from history..

    Over ten years ago someone (Eric Youngdale I guess) stuck a panic check
    for DMA over 16MBytes in the AHA 1542 ISA SCSI driver. Last year it
    triggered. The panic probably saved someone from corruption and meant the
    bug could be fixed.

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      Last update: 2007-05-18 17:11    [W:0.033 / U:60.120 seconds]
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