Re: [PATCH v3] gpio: exar: set value when external pull-up or pull-down is present

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Tue, Nov 12, 2024 at 5:09 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Tue, Nov 05, 2024 at 04:39:38PM +0200, Andy Shevchenko wrote:
> > On Tue, Nov 05, 2024 at 12:45:23PM +0530, Sai Kumar Cholleti wrote:
> > > Setting GPIO direction = high, sometimes results in GPIO value = 0.
> > >
> > > If a GPIO is pulled high, the following construction results in the
> > > value being 0 when the desired value is 1:
> > >
> > > $ echo "high" > /sys/class/gpio/gpio336/direction
> > > $ cat /sys/class/gpio/gpio336/value
> > > 0
> > >
> > > Before the GPIO direction is changed from an input to an output,
> > > exar_set_value() is called with value = 1, but since the GPIO is an
> > > input when exar_set_value() is called, _regmap_update_bits() reads a 1
> > > due to an external pull-up.  regmap_set_bits() sets force_write =
> > > false, so the value (1) is not written.  When the direction is then
> > > changed, the GPIO becomes an output with the value of 0 (the hardware
> > > default).
> > >
> > > regmap_write_bits() sets force_write = true, so the value is always
> > > written by exar_set_value() and an external pull-up doesn't affect the
> > > outcome of setting direction = high.
> > >
> > >
> > > The same can happen when a GPIO is pulled low, but the scenario is a
> > > little more complicated.
> > >
> > > $ echo high > /sys/class/gpio/gpio351/direction
> > > $ cat /sys/class/gpio/gpio351/value
> > > 1
> > >
> > > $ echo in > /sys/class/gpio/gpio351/direction
> > > $ cat /sys/class/gpio/gpio351/value
> > > 0
> > >
> > > $ echo low > /sys/class/gpio/gpio351/direction
> > > $ cat /sys/class/gpio/gpio351/value
> > > 1
> >
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
>
> Does this need to be applied, Bart?
> Seems it is missed in your branches...
>

Maybe if the author used get_maintainers.pl as they should, I would
have noticed this earlier?

I have some other fixes to pick up so I'll send this later in the merge window.

Bart