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

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Message-ID: <52373D6D.4010109@overkiz.com>
Date:	Mon, 16 Sep 2013 19:18:37 +0200
From:	boris brezillon <b.brezillon@...rkiz.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Rob Landley <rob@...dley.net>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Richard Genoud <richard.genoud@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH alt 4/4] pinctrl: at91: rework debounce configuration

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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