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    SubjectRe: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq
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    On Fri, Feb 3, 2012 at 00:05, H. Peter Anvin <hpa@linux.intel.com> wrote:
    > On 02/01/2012 05:05 PM, James Bottomley wrote:
    >>
    >>
    >> Incidentally, the last time this came up was with mpt fusion: for a
    >> write to a 64 bit register, it didn't care about order, but it did care
    >> about interleaving as in if you write one half of a 64 bit register and
    >> then write to another register, the 64 bit register effectively gets
    >> written with zeros in the part you didn't write to, so we had to put a
    >> spin lock in the open coded writeb/w/l/q() to make sure the card didn't
    >> get interleaved writes.
    >>
    >
    > There are always going to be hardware which have specific needs, and for
    > those open-coding makes sense, but the littleendian/bigendian pair is going
    > to cover ~90% of users and make sense to can.
    >
    > I worked myself on a driver (which sadly never shipped) which had an WC
    > window and a UC window... the final write in a series had a completion bit
    > in it and would go to the UC window after setting up a whole chunk of
    > operations in the WC window (writing UC memory flushes WC memory ahead of
    > it.)
    >
    > Thus, the two-part breakdown of writeq() to the UC window had to write the
    > low half to the WC window instead.  This is clearly not generic.
    >
    >        -hpa
    >
    >

    Because of my ignorant, I don't know the words "UC window" and "WC window"
    in this context. Could you teach me?

    --
    Hitoshi Mitake
    h.mitake@gmail.com
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