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    SubjectRe: [RFC] Proposal: common kernel-wide GPIO interface
    Ben Dooks wrote:
    > On Sun, Jul 30, 2006 at 03:08:11PM +0200, Robert Schwebel wrote:
    >> Chris,
    >> On Fri, Jul 28, 2006 at 09:44:40PM +0100, Chris Boot wrote:
    >>> I propose to develop a common way of registering and accessing GPIO pins on
    >>> various devices.
    >> I've attached the gpio framework we have developed a while ago; it is
    >> not ready for upstream, only tested on pxa and has probably several
    >> other drawbacks, but may be a start for your activities. One of the
    >> problems we've recently seen is that for example on PowerPCs you don't
    >> have such a clear "this is gpio pin x" nomenclature, so the question
    >> would be how to do the mapping here.
    > Right, my $0.02 worth:


    Some very interesting comments and suggestions! Thanks very much for all the
    info, that's exactly the sort of stuff I needed.

    > 3) The sysfs interface should be configurable, as systems
    > with lots of GPIO would end up with large numbers of
    > files and directories in sysfs.

    My current idea is to divide the interfaces by GPIO device and port. I've so far
    not seen a GPIO device that couldn't be divided into ports of <= 32 bits. How
    wide can a 'port' actually become?

    Somehow I think that a separate device/file for each pin or possibly even port
    might not be a wise idea. For example, twiddling individual pins on a GPIO when
    you connect an LCD, I2C, or SPI interface seems extremely inefficient...

    > 4) you probably want to ensure pull-up resistors are off if the
    > output is being driven.

    Yes, very good idea! So far I haven't managed to fry any chips by driving a
    pulled up/down output, but it's so easy to make the mistake...


    Chris Boot

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