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

From: Linus Walleij <linus.walleij@linaro.org>
To: neil.armstrong@linaro.org
Cc: Abel Vesa <abel.vesa@linaro.org>, Andy Gross <agross@kernel.org>,
	Bjorn Andersson <andersson@kernel.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	"linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>
Subject: Re: [PATCH v2 2/4] dt-bindings: pinctrl: qcom,tlmm-common: document i2c pull property
Date: Sat, 26 Nov 2022 22:53:57 +0100	[thread overview]
Message-ID: <CACRpkdbqjNJH_QvWyEPceUUxRQ2tOpErNOWA0rg5GNwq7PfUFQ@mail.gmail.com> (raw)
In-Reply-To: <8602cacd-f552-e843-5c17-681b099069a3@linaro.org>

On Fri, Nov 25, 2022 at 1:40 PM <neil.armstrong@linaro.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.

Yours,
Linus Walleij