gpio: fix locking open drain IRQ lines

We provided the right semantics on open drain lines being
by definition output but incidentally the irq set up function
would only allow IRQs on lines that were "not output".

Fix the semantics to allow output open drain lines to be used
for IRQs.

Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Tested-by: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Russell King <linux@armlinux.org.uk>
Cc: stable@vger.kernel.org # v5.3+
Link: https://lore.kernel.org/r/20200527140758.162280-1-linus.walleij@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Author: Linus Walleij

drivers/gpio/gpiolib.c

@@ -4220,7 +4220,9 @@ int gpiochip_lock_as_irq(struct gpio_chip *gc, unsigned int offset)
 		}
 	}
 
-	if (test_bit(FLAG_IS_OUT, &desc->flags)) {
+	/* To be valid for IRQ the line needs to be input or open drain */
+	if (test_bit(FLAG_IS_OUT, &desc->flags) &&
+	    !test_bit(FLAG_OPEN_DRAIN, &desc->flags)) {
 		chip_err(gc,
 			 "%s: tried to flag a GPIO set as output for IRQ\n",
 			 __func__);
@@ -4283,7 +4285,12 @@ void gpiochip_enable_irq(struct gpio_chip *gc, unsigned int offset)
 
 	if (!IS_ERR(desc) &&
 	    !WARN_ON(!test_bit(FLAG_USED_AS_IRQ, &desc->flags))) {
-		WARN_ON(test_bit(FLAG_IS_OUT, &desc->flags));
+		/*
+		 * We must not be output when using IRQ UNLESS we are
+		 * open drain.
+		 */
+		WARN_ON(test_bit(FLAG_IS_OUT, &desc->flags) &&
+			!test_bit(FLAG_OPEN_DRAIN, &desc->flags));
 		set_bit(FLAG_IRQ_IS_ENABLED, &desc->flags);
 	}
 }