linux-kernel - Re: [PATCH v7 3/5] ARM: dts: stm32: Add I2C1 support for STM32F429 SoC

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Message-ID: <CAOAejn1zHMFNiGc-wVbbkC1-JFzG3sjnnUJogtCp9EeAkWsV5A@mail.gmail.com>
Date:   Fri, 23 Dec 2016 14:09:21 +0100
From:   "M'boumba Cedric Madianga" <cedric.madianga@...il.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Patrice Chotard <patrice.chotard@...com>,
        linux@...linux.org.uk, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/5] ARM: dts: stm32: Add I2C1 support for STM32F429 SoC

Hi,


2016-12-22 20:11 GMT+01:00 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>:
> Hello,
>
> On Thu, Dec 22, 2016 at 02:35:02PM +0100, M'boumba Cedric Madianga wrote:
>> @@ -337,6 +350,16 @@
>>                                       slew-rate = <2>;
>>                               };
>>                       };
>> +
>> +                     i2c1_pins_b: i2c1@0 {
>> +                             pins1 {
>> +                                     pinmux = <STM32F429_PB9_FUNC_I2C1_SDA>;
>> +                                     drive-open-drain;
>> +                             };
>> +                             pins2 {
>> +                                     pinmux = <STM32F429_PB6_FUNC_I2C1_SCL>;
>> +                             };
>
> the second doesn't need the open-drain property? Why?
I thought that open-drain was only needed for SDA line.
But after double-checking I2C specification, it seems that SDA and SCL
lines need open-drain or open-collector to perform the wired-AND
function.
I will do some trials with this config and will fix it in the V8.
Thanks

>
>> +                     };
>>               };
>
> Best regards
> Uwe
>
> --
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |