linux-kernel - Re: [PATCH v3 3/7] arm: dts: dt-bindings: Add Renesas RZ pinctrl header

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Date:   Thu, 30 Mar 2017 10:15:05 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Chris Brandt <Chris.Brandt@...esas.com>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        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 v3 3/7] arm: dts: dt-bindings: Add Renesas RZ pinctrl header

On Wed, Mar 29, 2017 at 4:55 PM, Chris Brandt <Chris.Brandt@...esas.com> wrote:
> On Wednesday, March 29, 2017, Linus Walleij wrote:
>> On Fri, Mar 24, 2017 at 4:22 PM, Jacopo Mondi <jacopo+renesas@...ndi.org>
>> wrote:
>>
>> > Add dt-bindings for Renesas r7s72100 pin controller header file.
>> >
>> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
>>
>> > +/*
>> > + * Pin is bi-directional.
>> > + * An alternate function that needs both input/output functionalities
>> > +shall
>> > + * be configured as bidirectional.
>> > + * Eg. SDA/SCL pins of an I2c interface.
>> > + */
>> > +#define BI_DIR                 (1 << 3)
>>
>> Any specific reason why this should not simply be added to
>> include/linux/pinctrl/pinconf-generic.h
>> as PIN_CONFIG_BIDIRECTIONAL and parsed in drivers/pinctrl/pinconf-
>> generic.c from the (new) DT property "bidirectional" simply?
>
> I see your point. It would cut down from every driver out there
> inventing some new property or config instead of everyone just sharing
> a fixed set.
> Maybe someone else out there will end up having a need for a
> "bidirectional" option.

I was thinking about that one. It is a bit weird electrically, like what
kind of electronics is really bidirectional?

It seems like a fancy name for open drain/open source, what we
call "single ended" configuration. (See docs in
Documentation/gpio/driver.txt)

It would be great if you could check if that is what they mean,
actually.

> But, what do we do for Ethernet? All the pins are "normal" except just
> the MDIO pin needs to be bidirectional.

I see Geert clarified what we could do here.

Yours,
Linus Walleij