Messages in this thread | | | Date | Tue, 07 Aug 2007 15:46:36 +0100 | From | David Vrabel <> | Subject | Re: [patch 4/4] sdio: disable CD resistor |
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Pierre Ossman wrote: > On Tue, 07 Aug 2007 13:55:59 +0100 > David Vrabel <david.vrabel@csr.com> 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 <david.vrabel@csr.com> > > 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 -- 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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