linux-kernel - Re: [PATCH][RFC][resend after bogus] gpio-syscon: do not report bogus error

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Date: Fri, 12 Apr 2024 12:44:34 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: linus.walleij@...aro.org, brgl@...ev.pl, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC][resend after bogus] gpio-syscon: do not report bogus error

Hi Etienne,

thanks for your patch!

On Thu, Apr 11, 2024 at 5:35 PM Etienne Buira <etienne.buira@...e.fr> wrote:

> Do not call dev_err when gpio,syscon-dev is not set albeit unneeded.
> gpio-syscon is used with rk3328 chip, but this iomem region is
> documented in
> Documentation/devicetree/bindings/gpio/rockchip,rk3328-grf-gpio.yaml and
> does not look like to require gpio,syscon-dev setting.
>
> Signed-off-by: Etienne Buira <etienne.buira@...e.fr>
> X-Prefers: kind explanations over rotten tomatoes

If you look in drivers/gpio/gpio-syscon.c you see this:

        priv->syscon = syscon_regmap_lookup_by_phandle(np, "gpio,syscon-dev");
        if (IS_ERR(priv->syscon) && np->parent)
                priv->syscon = syscon_node_to_regmap(np->parent);

So the driver will attempt to grab the syscon from the parent if
it can't be located from a gpio,syscon-dev node.

But it's not optional, look in arch/arm64/boot/dts/rockchip/rk3328.dtsi:

        grf: syscon@...00000 {
                compatible = "rockchip,rk3328-grf", "syscon", "simple-mfd";
                reg = <0x0 0xff100000 0x0 0x1000>;
(...)
                grf_gpio: gpio {
                        compatible = "rockchip,rk3328-grf-gpio";
                        gpio-controller;
                        #gpio-cells = <2>;
                };

So indeed the parent is a sycon, and syscon_node_to_regmap(np->parent) will
be used to populate priv->syscon on RK3328.

So what you could do insteaf of the kludge is something like:

bool has_parent_syscon = false;

priv->syscon = syscon_regmap_lookup_by_phandle(np, "gpio,syscon-dev");
if (IS_ERR(priv->syscon) && np->parent) {
        priv->syscon = syscon_regmap_lookup_by_phandle(np, "gpio,syscon-dev");
        has_parent_syscon = true;
}
if (IS_ERR(priv->syscon))
        return PTR_ERR(priv->syscon);

Then when you get to the code you disable for the flag instead of:

if (!(priv->data->flags & GPIO_SYSCON_FEAT_NODEV)) {
(...)

instead do:

if (!has_parent_syscon) {
(...)

What do you think about this?

Yours,
Linus Walleij