linux-kernel - Re: [PATCH v2 2/4] dt-bindings: pinctrl: qcom,tlmm-common: document i2c pull property

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Message-ID: <f6ffd433-1652-fb4f-8657-928e7407ba5f@linaro.org>
Date:   Tue, 29 Nov 2022 09:15:02 +0100
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Abel Vesa <abel.vesa@...aro.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] dt-bindings: pinctrl: qcom,tlmm-common: document
 i2c pull property

Hi Linus,

On 26/11/2022 22:53, Linus Walleij wrote:
> On Fri, Nov 25, 2022 at 1:40 PM <neil.armstrong@...aro.org> wrote:
> 
>> As I understood, it enables an "I2C resistor" on the pin, removing the need
>> of an external pull-up resistor on the line.
>>
>> I assume the classical pull-up bias is not strong enough to replace an actual
>> resistor on the PCB.
> 
> In that case I think this should be an argument to bias-pull-up like:
> 
> bias-pull-up = <360000>;
> 
> Nominally the pull up is in ohms:
> 
>    bias-pull-up:
>      oneOf:
>        - type: boolean
>        - $ref: /schemas/types.yaml#/definitions/uint32
>      description: pull up the pin. Takes as optional argument on hardware
>        supporting it the pull strength in Ohm.
> 
> Then the driver can choose to shunt in this extra I2C resistance
> from the resistance passed as argument. So no special property
> is needed, provided you can get an idea about the resistance
> provided here.

I like this alternative, I'll try to figure out if we can find a value
to match against.

Thanks,
Neil

> 
> Yours,
> Linus Walleij