Re: [RFC PATCH 1/3] pinctrl: add new generic pinconf config for deglitchfilter

[boris brezillon]

On 27/08/2013 09:42, Nicolas Ferre wrote:
> 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...

Okay.

I'll propose a new patch series adding native support for OUTPUT 
configuration of at91 pins (add OUTPUT_HIGH/LOW),
and put this series in stand-by until a clear decision is made about 
generic pinconf.

Thanks,

Best Regards,

Boris
> Bye,
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