linux-kernel - RE: [PATCH 1/3] arm64: dts: imx8mm: Correct WDOG

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Message-ID: <DB3PR0402MB3916DF1213556C1187F5EB32F5070@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Mon, 12 Oct 2020 12:38:34 +0000
From:   Anson Huang <anson.huang@....com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "aford173@...il.com" <aford173@...il.com>,
        Daniel Baluta <daniel.baluta@....com>,
        "S.j. Wang" <shengjiu.wang@....com>,
        Peter Chen <peter.chen@....com>,
        "alifer.wsdm@...il.com" <alifer.wsdm@...il.com>,
        Abel Vesa <abel.vesa@....com>, Robin Gong <yibin.gong@....com>,
        Jun Li <jun.li@....com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 1/3] arm64: dts: imx8mm: Correct WDOG_B pin configuration

Hi, Krzysztof

> Subject: Re: [PATCH 1/3] arm64: dts: imx8mm: Correct WDOG_B pin
> configuration
> 
> On Fri, 9 Oct 2020 at 09:52, Anson Huang <Anson.Huang@....com> wrote:
> >
> > Different revision of i.MX8MM EVK boards may have different external
> > pull up registor design, some are enabled while some are NOT, to make
> > sure the WDOG_B pin works properly, better to enable internal pull up
> > resistor. Since enabling internal pull up resistor is NOT harmful and
> > having benefit of flexibility on different board design, just enable
> > it for all i.MX8MM boards.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > ---
> >  arch/arm64/boot/dts/freescale/imx8mm-beacon-som.dtsi | 2 +-
> >  arch/arm64/boot/dts/freescale/imx8mm-evk.dtsi        | 2 +-
> >  arch/arm64/boot/dts/freescale/imx8mm-var-som.dtsi    | 2 +-
> >  3 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/boot/dts/freescale/imx8mm-beacon-som.dtsi
> > b/arch/arm64/boot/dts/freescale/imx8mm-beacon-som.dtsi
> > index 6de86a4..a941301 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8mm-beacon-som.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8mm-beacon-som.dtsi
> > @@ -398,7 +398,7 @@
> >
> >                 pinctrl_wdog: wdoggrp {
> >                         fsl,pins = <
> > -
> MX8MM_IOMUXC_GPIO1_IO02_WDOG1_WDOG_B            0xc6
> > +
> MX8MM_IOMUXC_GPIO1_IO02_WDOG1_WDOG_B            0x166
> 
> Enabling pull up makes sense but you change other bits - disable Schmitt input
> and enable open drain. This change is not documented / explained in commit
> msg.

The Schmitt input is NOT necessary for WDOG_B pin which is for output ONLY.
The open drain is to let pull up voltage to decide the actual output voltage,
so it is NOT harmful for WDOG_B pin, hence we set it together.
I will send a V2 patch to add these info in commit msg.

Thanks,
Anson