gpiolib: Don't probe gpio_device if it's not the primary device

Dmitry reported[1] boot error messages caused by
commit 4731210c ("gpiolib: Bind gpio_device to a driver to enable fw_devlink=on by default").

gpio-1022 (cpu-pwr-req-hog): hogged as input
max77620-pinctrl max77620-pinctrl: pin gpio4 already requested by max77620-pinctrl; cannot claim for gpiochip1
max77620-pinctrl max77620-pinctrl: pin-4 (gpiochip1) status -22
max77620-pinctrl max77620-pinctrl: could not request pin 4 (gpio4) from group gpio4  on device max77620-pinctrl
gpio_stub_drv gpiochip1: Error applying setting, reverse things back
gpio_stub_drv: probe of gpiochip1 failed with error -22

This happens because when we try to probe a device, driver core calls
into pinctrl to set up the pins. However, if the GPIO DT node already
has a proper device created and probed, trying to probe the gpio_device
with a stub driver makes the pins be claimed twice. pinctrl doesn't like
this and throws an error.

So, this patch makes sure the gpio_stub_drv doesn't match with a
gpio_device if it's not the primary device for the fwnode.

[1] - https://lore.kernel.org/lkml/544ad0e4-0954-274c-8e77-866aaa5661a8@gmail.com/

Fixes: 4731210c ("gpiolib: Bind gpio_device to a driver to enable fw_devlink=on by default")
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20210205020730.1746354-1-saravanak@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpiolib.c

@@ -56,8 +56,10 @@
 static DEFINE_IDA(gpio_ida);
 static dev_t gpio_devt;
 #define GPIO_DEV_MAX 256 /* 256 GPIO chip devices supported */
+static int gpio_bus_match(struct device *dev, struct device_driver *drv);
 static struct bus_type gpio_bus_type = {
 	.name = "gpio",
+	.match = gpio_bus_match,
 };
 
 /*
@@ -4199,6 +4201,18 @@ void gpiod_put_array(struct gpio_descs *descs)
 }
 EXPORT_SYMBOL_GPL(gpiod_put_array);
 
+
+static int gpio_bus_match(struct device *dev, struct device_driver *drv)
+{
+	/*
+	 * Only match if the fwnode doesn't already have a proper struct device
+	 * created for it.
+	 */
+	if (dev->fwnode && dev->fwnode->dev != dev)
+		return 0;
+	return 1;
+}
+
 static int gpio_stub_drv_probe(struct device *dev)
 {
 	/*