gpiolib: Handle no pin_ranges in gpiochip_generic_config()

Similar to gpiochip_generic_request() and gpiochip_generic_free() the
gpiochip_generic_config() function needs to handle the case where there
are no pinctrl pins mapped to the GPIOs, usually through the gpio-ranges
device tree property.

Commit f34fd6e ("gpio: dwapb: Use generic request, free and
set_config") set the .set_config callback to gpiochip_generic_config()
in the dwapb GPIO driver so the GPIO API can set pinctrl configuration
for the corresponding pins. Most boards using the dwapb driver do not
set the gpio-ranges device tree property though, and in this case
gpiochip_generic_config() would return -EPROPE_DEFER rather than the
previous -ENOTSUPP return value. This in turn makes
gpio_set_config_with_argument_optional() fail and propagate the error to
any driver requesting GPIOs.

Fixes: 2956b5d ("pinctrl / gpio: Introduce .set_config() callback for GPIO chips")
Reported-by: Jisheng Zhang <jszhang@kernel.org>
Closes: https://lore.kernel.org/linux-gpio/ZdC_g3U4l0CJIWzh@xhacker/
Tested-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: esmil

drivers/gpio/gpiolib.c

@@ -2042,6 +2042,11 @@ EXPORT_SYMBOL_GPL(gpiochip_generic_free);
 int gpiochip_generic_config(struct gpio_chip *gc, unsigned int offset,
 			    unsigned long config)
 {
+#ifdef CONFIG_PINCTRL
+	if (list_empty(&gc->gpiodev->pin_ranges))
+		return -ENOTSUPP;
+#endif
+
 	return pinctrl_gpio_set_config(gc, offset, config);
 }
 EXPORT_SYMBOL_GPL(gpiochip_generic_config);