linux-kernel - Re: [PATCH v2 3/4] dt-bindings: Add pinctrl bindings for mt65xx/mt81xx.

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Date:	Thu, 2 Oct 2014 16:00:32 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	"Hongzhou.Yang" <srv_hongzhou.yang@...iatek.com>
Cc:	Rob Herring <robh+dt@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	srv_heupstream@...iatek.com, Sascha Hauer <kernel@...gutronix.de>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Hongzhou Yang <hongzhou.yang@...iatek.com>,
	"Joe.C" <yingjoe.chen@...iatek.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Vladimir Murzin <vladimir.murzin@....com>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, dandan.he@...iatek.com
Subject: Re: [PATCH v2 3/4] dt-bindings: Add pinctrl bindings for mt65xx/mt81xx.

On Tue, Sep 23, 2014 at 5:39 AM, Hongzhou.Yang
<srv_hongzhou.yang@...iatek.com> wrote:

> From: Hongzhou Yang <hongzhou.yang@...iatek.com>
>
> Add devicetree bindings for Mediatek SoC pinctrl driver.
>
> Signed-off-by: Hongzhou Yang <hongzhou.yang@...iatek.com>

I have worked on generic pin control bindings a bit because it
is getting out of hand with all these custom bindings.

See:
http://marc.info/?l=devicetree&m=141223584006648&w=2

Especially.

> +- mediatek,pinfunc: List of gpio number and function to mux.

A "GPIO number" and a "pin number" is not the same thing at all,
this is very confusing. Those are two separate number spaces.
This is likely about the pin numbers.

> +The mediatek,pinfunc can use defines directly,
> +which are already defind in boot/dts/mt8135-pinfunc.h.
> +
> +Optional subnode-properties:
> +- generic pin configuration option to use, bias-disable, bias-pull-down,
> +  bias-pull,up, output-low and output-high are valid.
> +  Example :
> +       i2c0_pins_a {
> +               mediatek,pinfunc = <MT8135_PIN_195_SDA1__FUNC_SDA1>;
> +               bias-disable;
> +       };

I don't like this approach at all.

I prefer that pins are put into groups named by strings, like "i2c0-pos0"
inside the driver and then connected to function with a certain
device-related name, such as "i2c0".

Then put the pin configuration (bias etc) in a separate node in the same
state definition like that:

i2c0_pins_a {
         function = "i2c0";
         groups = "i2c0-pos0";
};
i2c0_pins_b {
         bias-disable;
};

Yours,
Linus Walleij
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