Re: [PATCH v2 1/2] dt-bindings: gpio: nxp,pcf8575: add reset GPIO

Laurent Pinchart
2025-02-21T16:50:01Z

On Fri, Feb 21, 2025 at 11:14:26AM +0100, Quentin Schulz wrote:
> From: Quentin Schulz <quentin.schulz@cherry.de>
>
> 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 driven high
> for reset and then driven low, GPIO_ACTIVE_LOW means the GPIO will be
> driven low for reset and then driven high. If a GPIO is directly routed
> to RESETN pin on the IC without any inverter, GPIO_ACTIVE_LOW is thus
> expected.
>
> 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
>
> Tested-by: Heiko Stuebner <heiko@sntech.de> # exclusion logic
> Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
> ---
> .../devicetree/bindings/gpio/nxp,pcf8575.yaml | 38 ++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml b/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml
> index 3718103e966a13e1d77f73335ff73c18a3199469..633ac5cfa04a10bcbb748b6580938cddae9e5596 100644
> --- a/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml
> +++ b/Documentation/devicetree/bindings/gpio/nxp,pcf8575.yaml
> @@ -73,6 +73,44 @@ properties:
>
> wakeup-source: true
>
> + reset-gpios:
> + maxItems: 1
> + description:
> + description:
> + GPIO controlling the (reset active LOW) RESET# pin.
> +
> + The active polarity of the GPIO must translate to the low state
> + of the RESET# pin on the IC, i.e. if a GPIO is directly routed
> + to the RESET# pin without any inverter, GPIO_ACTIVE_LOW is
> + expected.

I'd reflow this text to 80 columns, like the next paragraph.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +
> + 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