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    SubjectRe: [PATCH v5 2/4] gpiolib: Add ability to get GPIO direction
    On Wed, Mar 09, 2011 at 04:53:56PM -0600, Peter Tyser wrote:
    > On Tue, 2011-03-08 at 12:13 +0000, Alan Cox wrote:
    > > > I don't object to a callback hook. My objection is how it is bodged
    > > > on to work around limitations to the direction being cached in the
    > > > flags variable. I want to see a solution that either depends entirely
    > > > on the callback, or completely fixes the problems with the cached
    > > > value by allowing the driver to update it.
    > >
    > > Doing it all by callback might actually fix a lot of the problems because
    > > it can handle all kinds of 'unknowns'. If the callbacks for set/get
    > > optionally pass a char buffer as well even the /proc interface just comes
    > > out in the wash as the device can return a string to populate the status
    > > or to be parsed (obviously with most h/w using the default method which
    > > is in/out)
    > I like the callback-only implementation also.
    > > However who then does the enforcement of gpio_foo calls if the flag is
    > > not cached, does that end up in each driver or is there still a cache of
    > > some form ?
    > What enforcement are you referring to? I was envisioning no cached
    > directions at the gpiolib level, eg replace all the current references
    > that check desc->flag for direction with calls to chip->get_direction().
    > If a GPIO chip's hardware didn't support reading the direction of a pin
    > (eg the pcf857x chip), it would have to use its own caching to maintain
    > an accurate representation of its pins directions. Is this concept in
    > line with what you were picturing?

    I agree. Trash the cache in gpiolib. Make drivers do it (or use a
    stock library function if they don't have the facility).


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