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    SubjectRe: [PATCH 3/3] gpiolib: use chip->names for symlinks, always use gpioN for device names
    On Thu, 2009-12-10 at 20:13 -0800, David Brownell wrote:
    > On Thursday 10 December 2009, Greg KH wrote:
    > >
    > > > IMO a "good" solution in this space needs to accept that
    > > > those names are not going to be globally unique ... but
    > > > that they'll be unique within some context, of necessity.
    > > >
    > > > If Greg doesn't want to see those names under classes,
    > > > so be it ... but where should they then appear?
    > >
    > > As a sysfs file within the device directory called 'name'? Then just
    > > grep through the tree to find the right device, that also handles
    > > duplicates just fine, right?
    > I want a concrete example. Those chip->names things don't
    > seem helpful to me though...
    > If for example I were building a JTAG adapter on Linux, it
    > might consist of a spidev node (chardev) plus a handful of
    > GPIOs. So "the device directory" would be the sysfs home
    > of that spidev node (or some variant)? And inside that
    > directory would be files named after various signals that
    > are used as GPIOs ... maybe SRST, TRST, and DETECT to start
    > with? Holding some cookie that gets mapped to those GPIO's
    > sysfs entries?

    If you've got a spidev node then you've got a dev to pass to
    gpio_export_link, all's right with the world. I think the best thing
    (which I think is what Greg was thinking) would be to
    have /sys/class/gpio/gpioN/name which reads null unless the kernel has
    registered a name against that gpio.

    Now I don't like the chip->name thing as a way to hold these labels, I'd
    prefer an IDR indexed by gpio number, but that's an implementation
    detail for later.

    A concrete use case: I've got a board here, the support patch for which
    will hopefully appear in a few days. On it I've got an 8-bit uC which
    does a bunch of I/O and on certain conditions, toggles gpio lines so a
    userspace daemon knows what's going on. At the moment, I
    have /sys/class/<board name>/ which exports things like revision
    information as well as attributes telling me which gpio numbers are used
    for which purpose. My scripts therefore look something like

    echo 1 > /sys/class/gpio/gpio`cat /sys/class/<board-name>/ack-gpio`/value

    I'm actually fairly happy with that but I don't pretend it's everyone's
    cup of tea. The point is though, the microprocessor has no in-kernel
    incarnation except these few gpio so there's no convenient dev node to
    link the names through; gpio_export_link() isn't useful.

    This problem could be solved as I have, but it could equally-well be
    solved by exporting gpioN/name attributes which I could search for.


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