linux-kernel - RE: [PATCH v2 2/7] dt-bindings: pinctrl: Add RZ/A1 bindings doc

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Message-ID: <SG2PR06MB1165276F957CE63DBE0A55268A350@SG2PR06MB1165.apcprd06.prod.outlook.com>
Date:   Wed, 29 Mar 2017 12:38:21 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     jacopo <jacopo@...ndi.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     Jacopo Mondi <jacopo+renesas@...ndi.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 v2 2/7] dt-bindings: pinctrl: Add RZ/A1 bindings doc

Adding my 2 cents here:

On Wednesday, March 29, 2017, jacopo wrote:
> > > If you really do we may need to go for u64 but ... really? Is there
> > > a rational reason for that other than "we did it like this first"?
> > >
> > > I do not understand the notion of "flags" here. I hope that is not
> > > referring
> >
> > Flags refers to BI_DIR, SWIO_IN, and SWIO_OUT, from
> > https://patchwork.kernel.org/patch/9643047/
> >
> > 32-bit should be enough to cover pins, function, and flags.
> >
> 
> Geert already replied, but to avoid any confusion I'll try to remove from
> driver the use of "pin config" when referring to this three flags, which
> are just additional informations the pin controller needs to perform pin
> muxing properly. They're not related the standard pin config properties
> (pull-up/down, bias etc.. actually our hardware does not even support
> these natively)
> 
> > > to pin config, because I expect that to use the standard pin config
> > > bindings outside of the pinmux value which should just define the
> > > pin+function combo:
> > >
> > > node {
> > >     pinmux = <PIN_NUMBER_PINMUX>;
> > >     GENERIC_PINCONFIG;
> > > };
> > >
> > > Example from Mediatek:
> > >
> > > i2c1_pins_a: i2c1@0 {
> > >     pins {
> > >         pinmux = <MT8135_PIN_195_SDA1__FUNC_SDA1>,
> > >                         <MT8135_PIN_196_SCL1__FUNC_SCL1>;
> >
> > If we follow this example, then we can list all combinations in
> > include/dt-bindings/pinctrl/r7s72100-pinctrl.h, instead of creating
> > the value by combining the bits using a macro where we need it in the
> DTS.
> >
> > It's gonna be a long list, though...
> >
> 
> I'm strongly in favour of something like
>     pinmux = <PIN(1, 4) | FUNC# | FLAGS>, .... ;
> 
> opposed to
>     pinmux = <PIN1_4_FUNC#_FLAGS>, ... ;


I agree. I like "<PIN(1, 4) | FUNC# | FLAGS>".



> Not only because it will save use from having a loong list(*) of macros
> that has to be kept up to date when/if new RZ hardware will arrive, but
> also because of readability and simplicity for down-stream and BSP users.
> Speaking of which, I would like to know what does Chris think of this.

The list of macros would be very long, especially against the different
packaging version of the RZ/A1 series. 11 ports, 16-pins for each port, 8 different
function options for each pin....2 different package/pin variations.

And at the end of the day....there is no benefit for the user over just using
a macro.


A little about "this controller" for the RZ/A1: In my opinion it's a one-shot usage.
I don't foresee future RZ/A SoCs using this exact pin controller.
The reason for the "FLAGS" is to work around a quirky hardware design (in my opinion).

However, future RZ/A SoCs will use a 'similar' type controller where each pin has 8 function
options (but the FLAGs won't be needed anymore...as far as I can see...).

So I foresee the DT interface staying more or less the same, but the underlying register
setup in the driver Will change (become more simple).


Now...if we can only convince the R-Car guys to move to a more simple pin-mux controller...


Chris