linux-kernel - Re: [PATCH 1/3] dt-bindings: pinctrl: Add bindings for mscc,ocelot-sgpio

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Date:   Tue, 26 May 2020 11:20:44 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Lars Povlsen <lars.povlsen@...rochip.com>
Cc:     SoC Team <soc@...nel.org>, 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 1/3] dt-bindings: pinctrl: Add bindings for mscc,ocelot-sgpio

On Mon, May 25, 2020 at 4:38 PM Lars Povlsen <lars.povlsen@...rochip.com> wrote:

> Yes, the problem is they're not in sequence. F.ex. you could have ports
> 0,1 enabled, skip 2,3,4 and have 5,6,7 enabled.

Just use disabled nodes.

That would look like this in my idea of a device tree:

pinctrl@nnn {
    gpio0: gpio@0 {
        compatible = "foo";
        status = "ok";
        ....
    };
    gpio1: gpio@1 {
        compatible = "foo";
        status = "ok";
        ....
    };
    gpio2: gpio@2 {
        compatible = "foo";
        status = "disabled";
        ....
    };
    gpio3: gpio@3 {
        compatible = "foo";
        status = "disabled";
        ....
    };
    gpio4: gpio@4 {
        compatible = "foo";
        status = "disabled";
        ....
    };
    gpio5: gpio@5 {
        compatible = "foo";
        status = "ok";
        ....
    };
    gpio6: gpio@6 {
        compatible = "foo";
        status = "ok";
        ....
    };
    gpio7: gpio@7 {
        compatible = "foo";
        status = "ok";
        ....
    };
};

It is common to use the status to enable/disable nodes like this.

In the Linux kernel is is possible to iterate over these subnodes and
check which ones are enabled and disabled while keeping the
index by using something like:

i = 0;
struct device_node *np, *child;
for_each_child_of_node(np, child) {
    if (of_device_is_available(child)) {
        pr_info("populating device %d\n", i);
    }
    i++;
}

Certainly you can use i in the above loop to populate your registers
etc from an indexed array.

This way the consumers can pick their GPIO from the right port
and everything just using e.g.
my-gpios = <&gpio6 4 GPIO_OUT_LOW>;

Yours,
Linus Walleij