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    SubjectRe: [patch 4/4] sdio: disable CD resistor
    Pierre Ossman wrote:
    > On Tue, 07 Aug 2007 13:55:59 +0100
    > David Vrabel <> wrote:
    >> sdio: disable CD resistor
    >> Disable the card detect resistor to ensure all data lines are equally
    >> loaded. Not doing this can have a negative impact on buses with
    >> marginal signal quality.
    >> Signed-off-by: David Vrabel <>
    > I'm not sure about this. I've seen several hosts which lack a
    > mechanical detect switch.

    If host is correctly designed it will have identical pull-ups on all the
    DAT lines, and therefore this internal pull-up should be disconnected.

    However, given that disabling the pull-up may cause 4 bit transfers to
    fail on hardware that omits a host-side pull-up on DAT3 I agree that the
    resistor should remain enabled.

    Is there an example driver for a host that uses pin 1/DAT3 sensing for
    card detection? I'm curious about how removal detections work.

    App Note on card detection goes into the use of this resistor in more
    detail but I don't believe this document is publicly available :(.

    David Vrabel, Software Engineer, Drivers group Tel: +44 (0)1223 692562
    CSR plc, Churchill House, Cambridge Business Park, Cowley Road, CB4 0WZ

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