The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin that is used to reset the I2C GPIO expander. One needs to hold this pin low for at least 4us and the reset should be finished after about 100us according to the datasheet[1]. Once the reset is done, the "registers and I2C-bus state machine will be held in their default state until the RESET input is once again HIGH.". Because the logic is reset, the latch values eventually provided in the Device Tree via lines-initial-states property are inapplicable so they are simply ignored if a reset GPIO is provided. This is eventually enforced by the Device Tree binding by making sure both cannot be present at the same time. Finally, the reset-gpios property is specific to PCA9670, PCA9671, PCA9672 and PCA9673 so make it specific to those chips. [1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 and fig 22. Signed-off-by: Quentin Schulz <quentin.schulz@xxxxxxxxx> --- Quentin Schulz (2): dt-bindings: gpio: nxp,pcf8575: add reset GPIO gpio: pcf857x: add support for reset-gpios on (most) PCA967x .../devicetree/bindings/gpio/nxp,pcf8575.yaml | 33 ++++++++++++++++++++++ drivers/gpio/gpio-pcf857x.c | 29 +++++++++++++++++-- 2 files changed, 59 insertions(+), 3 deletions(-) --- base-commit: 6537cfb395f352782918d8ee7b7f10ba2cc3cbf2 change-id: 20250219-pca976x-reset-driver-c9aa95869426 Best regards, -- Quentin Schulz <quentin.schulz@xxxxxxxxx>
