gpiolib: fix up emulated open drain outputs

gpiolib has a corner case with open drain outputs that are emulated.
When such outputs are outputting a logic 1, emulation will set the
hardware to input mode, which will cause gpiod_get_direction() to
report that it is in input mode. This is different from the behaviour
with a true open-drain output.

Unify the semantics here.

Cc: <stable@vger.kernel.org>
Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpiolib.c

@@ -220,6 +220,14 @@ int gpiod_get_direction(struct gpio_desc *desc)
 	chip = gpiod_to_chip(desc);
 	offset = gpio_chip_hwgpio(desc);
 
+	/*
+	 * Open drain emulation using input mode may incorrectly report
+	 * input here, fix that up.
+	 */
+	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags) &&
+	    test_bit(FLAG_IS_OUT, &desc->flags))
+		return 0;
+
 	if (!chip->get_direction)
 		return -ENOTSUPP;