gpiolib: don't allow OPEN_DRAIN & OPEN_SOURCE flags simultaneously

Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
the hardware actually supports enabling both at the same time the
electrical result would be disastrous.

Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -459,6 +459,15 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
 	if (lflags & ~GPIOHANDLE_REQUEST_VALID_FLAGS)
 		return -EINVAL;
 
+	/*
+	 * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
+	 * the hardware actually supports enabling both at the same time the
+	 * electrical result would be disastrous.
+	 */
+	if ((lflags & GPIOHANDLE_REQUEST_OPEN_DRAIN) &&
+	    (lflags & GPIOHANDLE_REQUEST_OPEN_SOURCE))
+		return -EINVAL;
+
 	/* OPEN_DRAIN and OPEN_SOURCE flags only make sense for output mode. */
 	if (!(lflags & GPIOHANDLE_REQUEST_OUTPUT) &&
 	    ((lflags & GPIOHANDLE_REQUEST_OPEN_DRAIN) ||