Re: [PATCH v3 1/2] dt-bindings: i2c-mux: Add property for settle time

From: Peter Rosin
Date: Mon Nov 01 2021 - 10:32:50 EST


On 2021-11-01 13:25, Horatiu Vultur wrote:
> Some HW requires some time for the signals to settle after the muxing is
> changed. Allow this time to be specified in device tree.
>
> Signed-off-by: Horatiu Vultur <horatiu.vultur@xxxxxxxxxxxxx>
> ---
> Documentation/devicetree/bindings/i2c/i2c-mux.yaml | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux.yaml b/Documentation/devicetree/bindings/i2c/i2c-mux.yaml
> index 24cac36037f5..4628ff6340c1 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-mux.yaml
> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux.yaml
> @@ -29,6 +29,12 @@ properties:
> '#size-cells':
> const: 0
>
> + settle-time-us:
> + default: 0
> + description:
> + The time required for the signals to settle. Currently only the
> + i2c-mux-gpmux driver supports this optional binding.

The information about how i2c-mux-gpmux is special is bound to go stale,
and I don't think we should mention such specific details in the binding.
What I meant was a generic warnings about optional bindings perhaps not
being supported by all drivers, along the lines of this from i2c.txt:

"These properties may not be supported by all drivers. However, if a driver
wants to support one of the below features, it should adapt these bindings."

However, I now notice that this sentence makes no sense. It looks like it
should be s/adapt/adopt/.

And, in the i2c-mux.yaml case it can simply say "Optional properties"
instead of "These properites" (which refers to a subset of properties
immediately below the text) since with a yaml binding it is always
clear which properties are optional and which are required. Lastly, I
guess this warning belongs in the description.

> +
> patternProperties:
> '^i2c@[0-9a-f]+$':
> $ref: /schemas/i2c/i2c-controller.yaml
>

Since this is the first optional property, you now need to specify what
properties are required, which is everything but settle-time-us. If you
don't, all properties are required. Which is not what we want...

Something like this should do it, I think:

required:
- compatible
- '#address-cells'
- '#size-cells'

Cheers,
Peter