Re: [PATCH v2 1/2] dt-bindings: gpio: introduce hog properties with less ambiguity

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Alexander,

On Wed, May 31, 2023 at 8:19 AM Alexander Stein
<alexander.stein@ew.tq-group.com> wrote:
> Am Dienstag, 30. Mai 2023, 17:19:45 CEST schrieb Uwe Kleine-König:
> > For active low lines the semantic of output-low and output-high is hard
> > to grasp because there is a double negation involved and so output-low
> > is actually a request to drive the line high (aka inactive).
> >
> > So introduce output-inactive and output-active with the same semantic as
> > output-low and output-high respectively have today, but with a more
> > sensible name.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > ---
> >  Documentation/devicetree/bindings/gpio/gpio.txt | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt
> > b/Documentation/devicetree/bindings/gpio/gpio.txt index
> > d82c32217fff..2f037bbd3ffa 100644
> > --- a/Documentation/devicetree/bindings/gpio/gpio.txt
> > +++ b/Documentation/devicetree/bindings/gpio/gpio.txt
> > @@ -209,15 +209,21 @@ Required properties:
> >  - gpios:      Store the GPIO information (id, flags, ...) for each GPIO to
> >             affect. Shall contain an integer multiple of the number of
> cells
> >             specified in its parent node (GPIO controller node).
> > +
> >  Only one of the following properties scanned in the order shown below.
> >  This means that when multiple properties are present they will be searched
> >  in the order presented below and the first match is taken as the intended
> >  configuration.
> > -- input:      A property specifying to set the GPIO direction as input.
> > -- output-low  A property specifying to set the GPIO direction as output
> > with -              the value low.
> > -- output-high A property specifying to set the GPIO direction as output
> > with -              the value high.
> > +- input:             A property specifying to set the GPIO direction as
> > input. +- output-inactive:   A property specifying to set the GPIO
> > direction as output +              with the inactive value
> (depending on the
> > line's polarity, +                 which is active-high by default)
> > +- output-active:     A property specifying to set the GPIO direction as
> > output +                   with the active value.
>
> I know this is essentially just renaming currently existing properties.
> But these mutual exclusive (boolean) properties make it impossible to change
> them in DT overlay. Any ideas how to support changing the output level onGPIO
> hogs in DT overlay?

That's a good point. And despite it not working, people do try to
stick e.g. /delete-node/ in .dtso files...

I assume you can sort of remove the existing hog subnode by adding
status = "disabled" in the DT overlay, and adding a new subnode to
configure the new output level?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds