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
