gpiolib: of: Introduce hook for missing gpio-ranges

Since commit 2ab73c6d83 ("gpio: Support GPIO controllers without pin-ranges")
the device tree nodes of GPIO controller need the gpio-ranges property to
handle gpio-hogs. Unfortunately it's impossible to guarantee that every new
kernel is shipped with an updated device tree binary.

In order to provide backward compatibility with those older DTB, we need a
callback within of_gpiochip_add_pin_range() so the relevant platform driver
can handle this case.

Fixes: 2ab73c6d83 ("gpio: Support GPIO controllers without pin-ranges")
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>
Link: https://lore.kernel.org/r/20220409095129.45786-2-stefan.wahren@i2se.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-of.c

@@ -931,6 +931,11 @@ static int of_gpiochip_add_pin_range(struct gpio_chip *chip)
 	if (!np)
 		return 0;
 
+	if (!of_property_read_bool(np, "gpio-ranges") &&
+	    chip->of_gpio_ranges_fallback) {
+		return chip->of_gpio_ranges_fallback(chip, np);
+	}
+
 	group_names = of_find_property(np, group_names_propname, NULL);
 
 	for (;; index++) {

include/linux/gpio/driver.h

@@ -492,6 +492,18 @@ struct gpio_chip {
 	 */
 	int (*of_xlate)(struct gpio_chip *gc,
 			const struct of_phandle_args *gpiospec, u32 *flags);
+
+	/**
+	 * @of_gpio_ranges_fallback:
+	 *
+	 * Optional hook for the case that no gpio-ranges property is defined
+	 * within the device tree node "np" (usually DT before introduction
+	 * of gpio-ranges). So this callback is helpful to provide the
+	 * necessary backward compatibility for the pin ranges.
+	 */
+	int (*of_gpio_ranges_fallback)(struct gpio_chip *gc,
+				       struct device_node *np);
+
 #endif /* CONFIG_OF_GPIO */
 };