Re: [RFC PATCH alt 4/4] pinctrl: at91: rework debounce configuration

[boris brezillon]

Hello Stephen,

On 16/09/2013 18:41, Stephen Warren wrote:
> On 09/14/2013 01:08 AM, boris brezillon wrote:
> > Hello Stephen,
> >
> > Le 14/09/2013 00:40, Stephen Warren a écrit :
> > > On 09/13/2013 01:53 AM, Boris BREZILLON wrote:
> > > > AT91 SoCs do not support per pin debounce time configuration.
> > > > Instead you have to configure a debounce time which will be used for all
> > > > pins of a given bank (PIOA, PIOB, ...).
> ...
> > > >    Required properties for pin configuration node:
> ...
> > > > -DEBOUNCE_VAL    (0x3fff << 17): debounce val.
> > > This change would break the DT ABI since it removes a feature that's
> > > already present.
> ...
> > > I suppose it's still up to the Atmel maintainers to decide whether this
> > > is appropriate, or whether the impact to out-of-tree DT files would be
> > > problematic.
> > >
> > > Assuming the DT ABI can be broken, I think I'd prefer to do so, rather
> > > than take "non-alt" patch 4/4, since a per-pin DEBOUNCE_VAL clearly
> > > doesn't correctly model the HW, assuming the patch description is
> > > correct. I don't think arguments re: the generic pinconf debounce
> > > property hold; if the Linux-specific/internal generic property doesn't
> > > apply, the DT binding should not be bent to adjust to it, but should
> > > rather still represent the HW itself.
> > What about the last point in my list: "reconfigure debounce after
> > startup" ?
> >
> > Here is an example that may be problematic:
> >
> > Let's say you have one device using multiple configuration of pins
> > ("default", "xxx", "yyy").
> > The "default" config needs a particular debounce time on a given pin and
> > the "xxx" and "yyy"
> > configs need different debounce time on the same pin.
> >
> > How would you solve this with this patch approach ?
> Each state has a different pin configuration node, and hence can specify
> a different debounce value. This patch has no impact on that (it just
> changes whether the state-specific node specifies the debounce value in
> a single standalone property, or encodes it into each entry in the pins
> property, all within the same node).
Actually it does: this patch removes the debounce time setting option from
the pin config description. The only thing you can do is enable or 
disable the
debounce filter.

The atmel,default-debounce-div property is not part of the pin group (or 
pin state)
node, it is a global property you define for the whole pinctrl 
controller (pinctrl node
property):

pinctrl {
        atmel,default-debounce-div=<100 /* PIOA div <=> ~3 ms */
                                                         50   /* PIOB 
div */
                                                         ...>;

        function {
            group {
                atmel,pins=<...>;
            };
        };
};

I can get the debounce time option in a separate property (as you're 
suggesting):

pinctrl {
    function {
        group {
            atmel,debounce=<1000>; /* debounce in usec */
            atmel,pins=<...>;
        };
    };
};

but it won't solve the primary issue, that is all the pin on a given 
bank (PIOA1 PIOA2, ...)
share the same debounce time.

Please tell me if I misunderstood your suggestion.

Best Regards,

Boris
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