[RFC PATCH alt 4/4] pinctrl: at91: rework debounce configuration
boris brezillon
b.brezillon at overkiz.com
Mon Sep 16 13:18:37 EDT 2013
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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