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    Subject[PATCH 3.16 009/254] scsi: use dma_get_cache_alignment() as minimum DMA alignment
    3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Huacai Chen <chenhc@lemote.com>

    commit 90addc6b3c9cda0146fbd62a08e234c2b224a80c upstream.

    In non-coherent DMA mode, kernel uses cache flushing operations to
    maintain I/O coherency, so scsi's block queue should be aligned to the
    value returned by dma_get_cache_alignment(). Otherwise, If a DMA buffer
    and a kernel structure share a same cache line, and if the kernel
    structure has dirty data, cache_invalidate (no writeback) will cause
    data corruption.

    Signed-off-by: Huacai Chen <chenhc@lemote.com>
    [hch: rebased and updated the comment and changelog]
    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/scsi/scsi_lib.c | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    --- a/drivers/scsi/scsi_lib.c
    +++ b/drivers/scsi/scsi_lib.c
    @@ -1671,11 +1671,13 @@ struct request_queue *__scsi_alloc_queue
    q->limits.cluster = 0;

    /*
    - * set a reasonable default alignment on word boundaries: the
    - * host and device may alter it using
    - * blk_queue_update_dma_alignment() later.
    + * Set a reasonable default alignment: The larger of 32-byte (dword),
    + * which is a common minimum for HBAs, and the minimum DMA alignment,
    + * which is set by the platform.
    + *
    + * Devices that require a bigger alignment can increase it later.
    */
    - blk_queue_dma_alignment(q, 0x03);
    + blk_queue_dma_alignment(q, max(4, dma_get_cache_alignment()) - 1);

    return q;
    }
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