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

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

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>

-- 
With Best Regards,
Andy Shevchenko