linux-kernel - Re: [PATCH v5 1/3] dt-bindings: pinctrl: Add bindings for pinctrl-microchip-sgpio driver

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Message-ID: <CACRpkdaFYoXFUuWow5s9TitrRDhMW=wiaxgfMcY6sQkYYgC-Lw@mail.gmail.com>
Date:   Fri, 9 Oct 2020 11:44:35 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Lars Povlsen <lars.povlsen@...rochip.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH v5 1/3] dt-bindings: pinctrl: Add bindings for
 pinctrl-microchip-sgpio driver

Hi Lars!

This is overall looking fine. Except for the 3 cell business. I just can't
wrap my head around why that is needed.

On Thu, Oct 8, 2020 at 3:05 PM Lars Povlsen <lars.povlsen@...rochip.com> wrote:

> +      '#gpio-cells':
> +        const: 3

So at the very least needs a description making it crystal clear why each
cell is needed, and used for since the standard bindings are not used.

+      sgpio_in2: gpio@0 {
+        reg = <0>;
+        compatible = "microchip,sparx5-sgpio-bank";
+        gpio-controller;
+        #gpio-cells = <3>;
+        ngpios = <96>;
+      };

So here reg = 0 and the out port has reg 1. Isn't that what you also put
in the second cell of the GPIO phandle? Then why? The driver
can very well just parse its own reg property and fill that in.

When you obtain a phandle like that:

gpios = <&sgpio_in2 11 0 GPIO_OUT_LOW>;

Isn't that 0 just duplicating the "reg"? Just parse reg when you set up
your driver state and put it as variable in the state container for your
driver state for this particular gpio_chip. No need to get it from
the phandle.

Yours,
Linus Walleij