Re: [PATCH v1 0/3] gpio: Add gpio-delay support

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Sun, Apr 16, 2023 at 2:42 PM Krzysztof Kozlowski
<krzysztof.kozlowski@xxxxxxxxxx> wrote:
>
> On 16/04/2023 13:33, Andy Shevchenko wrote:
> > On Sun, Apr 16, 2023 at 2:21 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> >> On 16/04/2023 13:14, Andy Shevchenko wrote:
> >>> On Sun, Apr 16, 2023 at 2:04 PM Krzysztof Kozlowski
> >>> <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> >>>> On 16/04/2023 11:36, Andy Shevchenko wrote:
> >>>>> On Sun, Apr 16, 2023 at 10:42 AM Krzysztof Kozlowski
> >>>>> <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> >>>>>> On 15/04/2023 17:06, Andy Shevchenko wrote:
> >>>>>>> On Fri, Apr 14, 2023 at 9:37 AM Alexander Stein
> >>>>>>> <alexander.stein@xxxxxxxxxxxxxxx> wrote:
> >>>>>>>> Am Dienstag, 11. April 2023, 11:34:16 CEST schrieb Andy Shevchenko:
> >>>>>>>>> On Tue, Apr 11, 2023 at 10:19 AM Alexander Stein
> >>>>>>>>> <alexander.stein@xxxxxxxxxxxxxxx> wrote:
> >>>>>
> >>>>> ...
> >>>>>
> >>>>>>>>> So, taking the above into consideration, why is it GPIO property to
> >>>>>>>>> begin with? This is PCB property of the certain platform design that
> >>>>>>>>> needs to be driven by a specific driver, correct?
> >>>>>>>>
> >>>>>>>> True this is induced by the PCB, but this property applies to the GPIO,
> >>>>>>>> neither the GPIO controller output, nor the GPIO consumer is aware of.
> >>>>>>>> So it has to be added in between. The original idea to add a property for the
> >>>>>>>> consumer driver is also rejected, because this kind of behavior is not limited
> >>>>>>>> to this specific driver.
> >>>>>>>> That's why the delay is inserted in between the GPIO output and GPIO consumer.
> >>>>>>>>
> >>>>>>>>> At the very least this is pin configuration (but external to the SoC),
> >>>>>>>>> so has to be a _separate_ pin control in my opinion.
> >>>>>>>>
> >>>>>>>> Sorry, I don't get what you mean by _separate_ pin control.
> >>>>>>>
> >>>>>>> As you mentioned above this can be applied theoretically to any pin of
> >>>>>>> the SoC, That pin may or may not be a GPIO or a pin that can be
> >>>>>>> switched to the GPIO mode. Hence this entire idea shouldn't be part of
> >>>>>>> the existing _in-SoC_ pin control driver if any. This is a purely
> >>>>>>> separate entity, but at the same time it adds a property to a pin,
> >>>>>>> hence pin control.
> >>>>>>> At the same time, it's not an SoC related one, it's a PCB. Hence _separate_.
> >>>>>>
> >>>>>> I don't think that anything here is related to pin control. Pin control
> >>>>>> is specific function of some device which allows different properties or
> >>>>>> different functions of a pin.
> >>>>>
> >>>>> Sorry, but from a hardware perspective I have to disagree with you.
> >>>>> It's a property of the _pin_ and not of a GPIO. Any pin might have the
> >>>>> same property. That's why it's definitely _not_ a property of GPIO,
> >>>>> but wider than that.
> >>>>
> >>>> I did not say this is a property of GPIO. I said this is nothing to do
> >>>> with pin control, configuration and pinctrl as is.
> >>>
> >>> Ah, I see. But still is a property of the pin on the PCB level.
> >>
> >> No, it is property of a circuit, so property of two pins and a wire
> >> between them. Not a property of one pin.
> >
> > Electrically speaking -- yes, software speaking, no, this is the
> > property of the one end (platfrom abstraction in the software) and as
> > you said, consumer which may be SoC, or the device connected to the
> > SoC (depending on the signal direction), or both (like pull-up for
> > I2C).
> >
> >>> That's
> >>> why I said that it should be like a "proxy" driver that has to be a
> >>> consumer of the pins on one side and provide the pins with this
> >>> property on the other.
> >>
> >> Not sure, why do you need it for anything else than GPIOs? What is the
> >> real world use case for proxy driver of non-GPIO lines?
> >
> > I2C is an example where we have something in between, which both of
>
> Are you sure you have RC (not just resistor) in I2C?

I'm talking about an analogue. In principle the pull-up is part of PCB
and not of the SoC.

> > the ends are using and this is the property of PCB, but luckily we
> > don't need anything special in the software for that, right? But from
> > the electrical point of view it's exactly a non-GPIO property. That's
> > why "proxy".
>
> Still I do not see any reason to call it anything else than GPIO. If you
> think that there is any other usage, please bring it as an real,
> non-theoretical example.

The first, which one I found, is time-stretched ADC. The idea is that
the portion of the signal is split to the phases and each phase is
passed via time stretcher for the low-speed ADC to be digitized. So,
if we have an SoC with 4+ ADCs, on the PCB one can add an externally
clocked mux and then 4+ time stretching lines and on the SoC side it
will be ADC (note, not a GPIO!).

-- 
With Best Regards,
Andy Shevchenko