On Mon, Nov 04, 2024 at 09:17:57PM +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
This...
> $ cat /sys/class/gpio/gpio351/value
> 1
>
> $ echo in > /sys/class/gpio/gpio351/direction
...this...
> $ cat /sys/class/gpio/gpio351/value
> 0
>
> $ echo low > /sys/class/gpio/gpio351/direction
...this...
> $ cat /sys/class/gpio/gpio351/value
> 1
> Fixes: 36fb7218e878 ("gpio: exar: switch to using regmap")
...and this lines have a trailing space.
> Signed-off-by: Sai Kumar Cholleti <skmr537@xxxxxxxxx>
> Signed-off-by: Matthew McClain <mmcclain@xxxxxxxxxxx>
Hmm... Missing Co-developed-by?
This SoB chain puzzles me a bit, the committer should go last AFAIR.
...
> + /*
> + * regmap_write_bits forces value to be written when an external
regmap_write_bits()
> + * pull up/down might otherwise indicate value was already set
Missing period at the end.
> + */
...
Other than above LGTM.
--
With Best Regards,
Andy Shevchenko
