Re: [PATCH v3 12/16] pinctrl: starfive: Add pinctrl driver for StarFive SoCs

[Emil Renner Berthing <kernel@esmil.dk>]

On Tue, 9 Nov 2021 at 10:34, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> On Tue, Nov 9, 2021 at 11:21 AM Emil Renner Berthing <kernel@esmil.dk> wrote:
> > On Tue, 9 Nov 2021 at 02:01, Linus Walleij <linus.walleij@linaro.org> wrote:
> > > On Tue, Nov 2, 2021 at 9:08 PM Andy Shevchenko
> > > <andy.shevchenko@gmail.com> wrote:
>
> ...
>
> > > > Linus any comments on this code (sorry if I missed your reply)? The
> > > > idea behind above is to skip all settings from the same category and
> > > > apply only the last one, e.g. if we have "bias set to X", ..., "bias
> > > > disable", ..., "bias set to Y", the hardware will see only the last
> > > > operation, i.e. "bias set to Y". I think it may not be the best
> > > > approach (theoretically?) since the hardware definitely may behave
> > > > differently on the other side in case of such series of the
> > > > configurations (yes, I have seen some interesting implementations of
> > > > the touchpad / touchscreen GPIOs that may be affected).
> > >
> > > That sounds weird. I think we need to look at how other drivers
> > > deal with this.
> > >
> > > To me it seems more natural that
> > > starfive_padctl_rmw(sfp, group->pins[i], mask, value);
> > > would get called at the end of each iteration of the
> > > for (i = 0; i < num_configs; i++) loop.
> >
> > That would work, but when the loop is done the end result would be
> > exactly the same.
>
> It seems we interpret the term "result" differently. The result when
> we talking about GPIOs is the series of pin state changes incl.
> configuration. This is how it should be recognized when programming
> hardware.
>
> >  The only difference is that the above would rapidly
> > "blink" the different states during the loop until it arrives at the
> > result. This would certainly be different, but it can never be the
> > intended behaviour and only a side-effect on how the pinctrl framework
> > works.
>
> Is it? That's what I'm trying to get an answer to. If you may
> guarantee this (the keywords "intended behaviour" and "side effect"),
> I wouldn't object.
>
> > The order the different states are blinked depends entirely on
> > how the pinctrl framework parses the device tree. I still think it
> > would be more natural to cleanly go to the end result without this
> > blinking.

Hmm.. but if going through the different states is what you want, then
wouldn't you need the device tree to have an ordered list of the
states rather than just a single node and also a way to tune how long
time the different states are blinked?