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

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Message-ID: <87pnappzun.fsf@soft-dev15.microsemi.net>
Date:   Wed, 27 May 2020 10:05:20 +0200
From:   Lars Povlsen <lars.povlsen@...rochip.com>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     Lars Povlsen <lars.povlsen@...rochip.com>,
        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


Linus Walleij writes:

> 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>;
>

Linux, thank you for your input, it is much appreciated. I will use the
pattern in the driver in the next revision.

The only issue is that the gpios on the same "port" have restrictions on
their status - they can only be enabled "all" or "none" for gpios that
map to the same port. F.ex. gpio0, gpio32, gpio64 and gpio96 must all be
enabled or disabled because at the hardware level you control the
_port_. But as I noted earlier, that could just be the driver enforcing
this.

Thanks again.

---Lars

> Yours,
> Linus Walleij

-- 
Lars Povlsen,
Microchip