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

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Date:   Thu, 15 Dec 2022 12:49:18 -0800
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Neil Armstrong <neil.armstrong@...aro.org>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        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

On Tue, Nov 29, 2022 at 09:15:02AM +0100, Neil Armstrong wrote:
> 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.

That is correct.

> > 
> > 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.
> 

The typical value for this resistor is 2.2kOhm.

Regards,
Bjorn