Hi Quentin, Thank you for the patch. On Thu, Feb 20, 2025 at 10:56:51AM +0100, Quentin Schulz wrote: > From: Quentin Schulz <quentin.schulz@xxxxxxxxx> > > A few of the I2C GPIO expander chips supported by this binding have a > RESETN pin to be able to reset the chip. The chip is held in reset while > the pin is low, therefore the polarity of reset-gpios is expected to > reflect that, i.e. a GPIO_ACTIVE_HIGH means the GPIO will be held low > for reset and released high, GPIO_ACTIVE_LOW means the GPIO will be held > high for reset and released low. I think the convention in DT is the opposite. The DT property is "reset-gpios", no "resetn-gpio", so the polarity should indicate how to drive the GPIO to assert a logical "reset". GPIO_ACTIVE_LOW should mean that the chip will be in reset when the physical GPIO is 0. Could DT maintainers confirm this ? > Out of the supported chips, only PCA9670, PCA9671, PCA9672 and PCA9673 > show a RESETN pin in their datasheets. They all share the same reset > timings, that is 4+us reset pulse[0] and 100+us reset time[0]. > > When performing a reset, "The PCA9670 registers and I2C-bus state > machine will be held in their default state until the RESET input is > once again HIGH."[1] meaning we now know the state of each line > controlled by the GPIO expander. Therefore, setting lines-initial-states > and reset-gpios both does not make sense and their presence is XOR'ed. > > [0] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf Fig 22. > [1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 > > Signed-off-by: Quentin Schulz <quentin.schulz@xxxxxxxxx> > --- > .../devicetree/bindings/gpio/nxp,pcf8575.yaml | 33 ++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > > diff --git a/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml b/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml > index 3718103e966a13e1d77f73335ff73c18a3199469..d08d3f848f82e74de949da16d26a810dc52a74e5 100644 > --- a/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml > +++ b/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml > @@ -73,6 +73,39 @@ properties: > > wakeup-source: true > > + reset-gpios: > + maxItems: 1 > + description: > + GPIO controlling the (reset active LOW) RESET# pin. > + > + Performing a reset makes all lines initialized to their input (pulled-up) > + state. > + > +allOf: > + - if: > + properties: > + compatible: > + not: > + contains: > + enum: > + - nxp,pca9670 > + - nxp,pca9671 > + - nxp,pca9672 > + - nxp,pca9673 > + then: > + properties: > + reset-gpios: false > + > + # lines-initial-states XOR reset-gpios > + # Performing a reset reinitializes all lines to a known state which > + # may not match passed lines-initial-states > + - if: > + required: > + - lines-initial-states > + then: > + properties: > + reset-gpios: false > + > patternProperties: > "^(.+-hog(-[0-9]+)?)$": > type: object > -- Regards, Laurent Pinchart
