Re: [PATCH 2/2] gpio: adg1712: add driver support

[Linus Walleij]

On Mon, Nov 10, 2025 at 1:32 PM Nuno Sá <noname.nuno@xxxxxxxxx> wrote:
> On Mon, 2025-11-10 at 11:30 +0100, Linus Walleij wrote:
> > Hi Antoniu,
> >
> > thanks for your patch!
> >
> > On Fri, Oct 31, 2025 at 5:08 PM Antoniu Miclaus
> > <antoniu.miclaus@xxxxxxxxxx> wrote:
> >
> > > Add driver support for the ADG1712, which contains four independent
> > > single-pole/single-throw (SPST) switches and operates with a
> > > low-voltage single supply range from +1.08V to +5.5V or a low-voltage
> > > dual supply range from ±1.08V to ±2.75V.
> > >
> > > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@xxxxxxxxxx>
> >
> > So tying into the binding discussion:
> >
> > GPIO means "general purpose input/output".
> >
> > I am really confused as whether this is:
> >
> > - General purpose - seems to be for the purpose of switching
> >   currents and nothing else.
> >
> > - Input/Output - It's switching something else and not inputting
> >   or outputting anything and this makes the driver look strange.
> >
> >
>
> Not the first time a part like this pops up [1]. At the time, the final
> conclusion was to go with gpiolib. Naturally you can think otherwise now :)

I think we might wanna go with gpiolib for the Linux internals, maybe
we want to add some kind of awareness or flag in gpiolib that this is
a switch and not an output we can control the level of?

I could think of this:

- Make .get() and .set() in struct gpio_chip return -ENOTIMP
  no getting and setting these "lines" because we really cannot
  control that, these lines will have the level of whatever is on
  the line we are switching.

- Implement .set_config() and implement the generic pin
  control property PIN_CONFIG_OUTPUT_ENABLE as 1
  to switch "on" and 0 for switch "off".
  See include/linux/pinctrl/pinconf-generic.h

This makes it possible to use the gpiolib in a way that is
non-ambiguous.

We might want to add consumer helpers in
include/linux/gpio/consumer.h such as:

#include <linux/pinctrl/pinconf-generic.h>

int gpiod_switch_enable(struct gpio_desc *desc)
{
   unsigned long cfg = pinconf_to_config_packed(PIN_CONFIG_OUTPUT_ENABLE, 1);

   return gpiod_set_config(desc, cfg);
}

int gpiod_switch_disable(struct gpio_desc *desc)
{
   unsigned long cfg = pinconf_to_config_packed(PIN_CONFIG_OUTPUT_ENABLE, 0);

   return gpiod_set_config(desc, cfg);
}

See e.g. rtd_gpio_set_config() in drivers/gpio/gpio-rtd.c for
an example of how the GPIO driver can unpack and handle
generic .set_config() options like this.

The binding however needs to be something separate like a proper switch binding
I think or we will confuse other operating systems.

Yours,
Linus Walleij