On Fri, Dec 23, 2016 at 2:09 PM, M'boumba Cedric Madianga <cedric.madia...@gmail.com> wrote: > 2016-12-22 20:11 GMT+01:00 Uwe Kleine-König <u.kleine-koe...@pengutronix.de>: >> 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 think I2C SDA/SCL must be open drain by definition. It also requires pull-up resistors, I guess you have these mounted on the board so you do not need pull-up from the pin controller? Yours, Linus Walleij