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

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Message-ID: <fecb2dd6-9be2-78dc-4598-cc338fbdc2a2@linaro.org>
Date:   Thu, 24 Nov 2022 14:24:10 +0100
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Abel Vesa <abel.vesa@...aro.org>
Cc:     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 24/11/2022 14:11, Linus Walleij wrote:
> On Wed, Nov 23, 2022 at 4:20 PM Abel Vesa <abel.vesa@...aro.org> wrote:
> 
>> From: Neil Armstrong <neil.armstrong@...aro.org>
>>
>> Document the new i2c_pull property introduced for SM8550 setting
>> an I2C specific pull mode on I2C able pins.
>>
>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> (...)
>> +      qcom,i2c-pull:
>> +        type: boolean
>> +        description: enable bias pull feature designed for I2C on pin
> 
> But what is this?
> 
> I2C buses are usually just plain old bias-high-impedance, high-z
> or open drain, wire-or or whatever you want to call it.
> 
> But now there is some special i2c mode, huh?
> 
> The description is pretty much "it is what it is"... can we have
> some explanation about what this means electrically speaking
> and why you cannot use bias-high-impedance?

I'll try to get some more info, but so far I only found what I wrote in the bindings.

Neil

> 
> Yours,
> Linus Walleij