Messages in this thread | | | Date | Tue, 27 Aug 2013 09:42:54 +0200 | From | Nicolas Ferre <> | Subject | Re: [RFC PATCH 1/3] pinctrl: add new generic pinconf config for deglitch filter |
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On 27/08/2013 08:16, boris brezillon : > On 27/08/2013 05:55, Stephen Warren wrote: >> On 08/26/2013 11:01 AM, boris brezillon wrote: >>> Hello Stephen, >>> >>> On 26/08/2013 18:50, Stephen Warren wrote: >>>> On 08/24/2013 03:35 PM, Boris BREZILLON wrote: >>>>> Add a new parameter to support deglitch filter configuration. >>>>> A deglitch filter works like a debounce filter but with a smaller >>>>> delay (nanoseconds). >>>> Why not use the existing debounce property, just with a small delay >>>> specified. It seems like that's exactly what the property is for? >>> That's one of the question I asked in my cover letter :-) >>> >>> Indeed the at91 deglitch filter delay is not configurable and is statically >>> assigned to half a master clk cycle (if master clk = 133MHz -> 8 ns). >>> The debounce property argument is currently expressed in usecs. >>> >>> This will result in always selecting the debounce filter (which is also >>> available on at91 SoCs) over the deglitch filter. >>> >>> Could we add a flag in the deglitch argument to specify the delay unit >>> (nsecs or usecs) ? >> If the value is hard-coded in HW, why not use non-zero (or 1) to enable >> and zero to disable? > > Indeed at91 pins support both deglitch and debounce filter and I have to > choose > between the two given the argument value (in usec). > > Here's what I can do: > > if (arg >= 1/2 * slowclock) /* debounce case */ > /* choose debounce filter and configure the delay > according to the given argument value */ > else /* deglitch case */ > /* choose deglitch filter */ > > > Slow clock is running at 32KHz which gives a 30 usec clock cycle.
I am not in favor for this kind of complicated heuristic. Deglitch and Debounce filters are different features in at91 (even if they pursuit the same goal). So I do prefer to let the user choose which feature is preferred for his application and add a different flag.
>> (this kind of thing is why I'm not convinced that generic pinconf works >> so well... What if we need psecs in the future?) > > Should I keep the at91 native pinconf binding and add the missing flags > to this binding > (OUTPUT configuration flags) ? > > This was another question I asked in my cover letter: wether or not the > generic pinconf > binding should be used.
The question is: how much this "generic" pinconf is... well... generic! And it is not a answer I can give. On the other hand, if the "generic" is not going to overcome the native pinctrl, I do not feel like switching to this at the cost of changing the whole dtsi/dts entries that we already have.
So, it is more to Linus and Stephen to give us clues about this...
Bye, -- Nicolas Ferre
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