Re: [PATCH] gpiolib: tolerate gpio-hogs lacking a hogging state

[Andy Shevchenko]

On Tue, Jul 14, 2026 at 12:30:53AM +0100, Daniel Golle wrote:
> Commit d1d564ec4992 ("gpio: move hogs into GPIO core") made
> gpiochip_add_hog() return -EINVAL for hog nodes lacking any of the
> 'input', 'output-low' or 'output-high' properties. The error is
> propagated by gpiochip_hog_lines() and fails registration of the
> whole GPIO chip.
> 
> The previous OF-specific implementation tolerated such nodes:
> of_parse_own_gpio() warned "no hogging state specified, bailing out"
> and of_gpiochip_add_hog() stopped processing the node without failing
> chip registration.
> 
> Some boards deliberately ship hog nodes without a hogging state in
> their base devicetree and supply the state via overlay, e.g. the PCIe
> slot key selection hogs on the BananaPi R4 Pro added in
> commit e309fa232d12 ("arm64: dts: mediatek: mt7988a-bpi-r4pro: rework
> pcie gpio-hog handling"), as the polarity set in the base devicetree
> could not be overridden from an overlay.
> 
> Booting such a board without an overlay applied now fails to register
> the gpiochip. On the BananaPi R4 Pro this means the MT7988A pinctrl
> device fails to probe, all peripherals including the console UART
> defer forever, and the board finally hangs when clk_disable_unused()
> gates the clocks of the UART still in use by earlycon:
> 
>   gpiochip_add_data_with_key: GPIOs 512..595 (pinctrl_moore) failed to register, -22
>   mt7988-pinctrl 1001f000.pinctrl: error -EINVAL: Failed to add gpio_chip
>   ...
>   clk: Disabling unused clocks
>   (hangs)
> 
> Restore the previous behaviour by warning about hog nodes lacking a
> hogging state and skipping them instead of failing the registration
> of the whole GPIO chip.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

...

> -	if (fwnode_property_present(fwnode, "input"))
> +	if (fwnode_property_present(fwnode, "input")) {
>  		dflags |= GPIOD_IN;
> -	else if (fwnode_property_present(fwnode, "output-low"))
> +	} else if (fwnode_property_present(fwnode, "output-low")) {
>  		dflags |= GPIOD_OUT_LOW;
> -	else if (fwnode_property_present(fwnode, "output-high"))
> +	} else if (fwnode_property_present(fwnode, "output-high")) {
>  		dflags |= GPIOD_OUT_HIGH;

For a fix I would make it less invasive and yes, break the style, by just
replacing

> -	else
> -		return -EINVAL;

with

	else {
		gpiochip_warn(gc, "%pfwP: no hogging state specified, bailing out\n",
			      fwnode);
		return 0;
	}

> +	} else {
> +		gpiochip_warn(gc, "%pfwP: no hogging state specified, bailing out\n",
> +			      fwnode);
> +		return 0;
> +	}

This leads patch directly to the point. The style can be modified later on.

-- 
With Best Regards,
Andy Shevchenko