Re: [PATCH v4 1/3] dt-bindings: i2c-gpio: Add properties for dealing with write-only SDA/SCL w/o pullup

[Rob Herring <robh@kernel.org>]

On Tue, Jan 17, 2023 at 09:36:05PM +0100, Heiner Kallweit wrote:
> There are slave devices that understand I2C but have read-only SDA and
> SCL. Examples are FD650 7-segment LED controller and its derivatives.
> Typical board designs don't even have a pull-up for both pins.
> Therefore add properties for not using open-drain. For write-only SCL
> we have a property already, add one for write-only SDA.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
> v4:
> - add no-pullup properties
> ---
>  .../devicetree/bindings/i2c/i2c-gpio.yaml        | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
> index e0d76d5eb..67898cc52 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
> +++ b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
> @@ -33,6 +33,10 @@ properties:
>        open drain.
>      maxItems: 1
>  
> +  i2c-gpio,sda-output-only:
> +    description: sda as output only
> +    type: boolean
> +
>    i2c-gpio,scl-output-only:
>      description: scl as output only
>      type: boolean
> @@ -63,6 +67,18 @@ properties:
>        GPIO line used for SCL into open drain mode, and that something is not
>        the GPIO chip. It is essentially an inconsistency flag.
>  
> +  i2c-gpio,sda-has-no-pullup:
> +    type: boolean
> +    description: sda is used in a non-compliant way and has no pull-up.
> +      Therefore disable open-drain. This property is mutually-exclusive
> +      with i2c-gpio,sda-open-drain.
> +
> +  i2c-gpio,scl-has-no-pullup:
> +    type: boolean
> +    description: scl is used in a non-compliant way and has no pull-up.
> +      Therefore disable open-drain. This property is mutually-exclusive
> +      with i2c-gpio,scl-open-drain.

The mutual-exclusion can be expressed as a schema instead:

allOf:
  - not:
      required:
        - i2c-gpio,scl-has-no-pullup
        - i2c-gpio,scl-open-drain
  - not:
      required:
        - i2c-gpio,sda-has-no-pullup
        - i2c-gpio,sda-open-drain

Using 'dependencies' with a schema would also work.

Rob