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    SubjectRe: What's left over.

    On Thu, 31 Oct 2002, Chris Wedgwood wrote:
    > It's synchronous and assume everything is synchronous. Lots of
    > hardware (most) doesn't work that way.

    Think of it another way: many users will likely _require_ atomic
    encryption / decryption (done in softirq contexts etc), and thus a
    synchronous interface. Also, it simplifies the code and makes it more

    Any hardware that needs to go off and think about how to encrypt something
    sounds like it's so slow as to be unusable. I suspect that anything that
    is over the PCI bus is already so slow (even if it adds no extra cycles of
    its own) that you're better off using the CPU for the encryption rather
    than some external hardware.

    In short, from what I can tell, there is no huge actual reason to ever
    allow a asynchronous interface. Such interfaces are likely fine for things
    like network cards that can do encryption on their own on outgoing or
    incoming packets, but that is not a general-purpose encryption engine, and
    would not merit being part of an encryption library anyway.

    [ Such a card is just a way to _avoid_ using the encryption library - the
    same way we can avoid using the checksumming stuff for network cards
    that can do their own checksums ]

    We'll see. I'd rather have a simpler interface that works for all relevant
    cases today, and then if external crypto chips end up being common and
    sufficiently efficient, we can always re-consider. Are the DMA-over-PCI
    roundtrip (and resulting cache invalidations) overheads really worth the
    extra hardware?


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