Re: [PATCH 4/5] dt-bindings: media: max9286: Add reverse channel amplitude

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Hi Jacopo,

On 16/03/2020 20:27, Jacopo Mondi wrote:
> The MAX9286 chip exposes registers to control the reverse channel
> amplitude signal. The channel amplitude has to be configured according
> to the connected remote serializer settings, in order to guarantee
> reliable communications.
> 
> Serializer might be pre-programmed and initialize with their reverse
> channel noise threshold level increased. While this is intended to
> increase the signal/noise immunity ratio on the channel, the
> deserializer should be initialized accordingly, with its channel
> amplitude increased to 170mV.
> 
> Add to the bindings documentation a required property to allow DTS users
> to specify the initial setting of the deserializer reverse channel and
> accommodate different serializer models.
> 

Same comments really as the other property, that these are highly
dependent upon the serializer which is connected, so I wonder if there's
a better way to describe that association / communication requirement.

> Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
> ---
>  .../bindings/media/i2c/maxim,max9286.yaml     | 21 +++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml b/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
> index ee8e0418b3f0..a1c56734a727 100644
> --- a/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
> +++ b/Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
> @@ -54,6 +54,25 @@ properties:
>      allOf:
>        - $ref: /schemas/types.yaml#/definitions/uint32
>  
> +  maxim,reverse-channel-amplitude:
> +    description: |
> +      The reverse channel amplitude initial value, in milliVolts. If the remote

Should there be a newline after milliVolts. ? That seems like a brief,
followed by a description but all flowing together?

> +      serializer is pre-programmed with an high reverse channel noise threshold,

/an/a/

> +      the deserializer channel amplitude shall initially be increased to 170mV
> +      to allow the two to communicate reliably. Likewise, if the remote
> +      serializer probes without an increased reverse channel noise threshold,
> +      the deserializer initial reverse channel amplitude should be set to 100mV
> +      to be later increased to 170mV after serializers have increased their

/after/after the/

> +      reverse channel noise threshold.
> +    maxItems: 1
> +    allOf:
> +      - $ref: /schemas/types.yaml#/definitions/uint32
> +    # The property can be easily expanded to support more values if needed,
> +    # but that's what's supported today by the driver.

Stating "that's what's supported today" seems a bit redundant...

> +    oneOf:
> +      - const: 100
> +      - const: 170
> +
>    ports:
>      type: object
>      description: |
> @@ -155,6 +174,7 @@ required:
>    - compatible
>    - reg
>    - maxim,overlap-window
> +  - maxim,reverse-channel-amplitude
>    - ports
>    - i2c-mux
>  
> @@ -177,6 +197,7 @@ examples:
>          poc-supply = <&camera_poc_12v>;
>          enable-gpios = <&gpio 13 GPIO_ACTIVE_HIGH>;
>          maxim,overlap-window = MAX9286_OVLP_WINDOW_DISABLED;
> +        maxim,reverse-channel-amplitude = <170>;
>  
>          ports {
>            #address-cells = <1>;
> 




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