linux-kernel - RE: [PATCH v5 10/10] arm: dts: genmai: Add ethernet pin group

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Date:   Fri, 28 Apr 2017 13:50:32 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>
CC:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh+dt@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 10/10] arm: dts: genmai: Add ethernet pin group

On Friday, April 28, 2017, Linus Walleij wrote:
> > Add pin configuration subnode for ETHER ethernet controller.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> (...)
> > +               pins_bidir {
> > +                       pinmux = <RZA1_PINMUX(3, 3, 2)>;/* P3_3 =
> ET_MDIO  */
> > +                       bi-directional;
> > +               };
> 
> So I'm against merging this until someone explains what "bi-directional"
> actually means, electrically speaking. What happens physically on this
> pin?
> 
> I think this just means open drain.
> 
> It is dangerous to merge things we don't understand.
> 
> Surely someone inside Renesas can answer this question.

I don't think this has anything to do with open drain because you need it for any pin that the peripheral IP block needs to transmit and receive over the same line, regardless of if it's a SDHI, I2C, Ethernet MDIO, etc...
It's more about of allowing the internal IP block signals to get hooked up to the IO pad signals.

Chris