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

[Heiner Kallweit <hkallweit1@gmail.com>]

On 18.01.2023 17:32, Rob Herring wrote:
> 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.
> 
Great, I wasn't aware of options to express mutually-exclusive properties.

I'll wait a little for other feedback regarding the series and then submit
a new version incl. the extended schema.

> Rob

Heiner