gpiolib: Don't prevent IRQ usage of output GPIOs

Upstream Linux deems using output GPIOs to generate IRQs as a bogus
use case, even though the BCM2835 GPIO controller is capable of doing
so. A number of users would like to make use of this facility, so
disable the checks.

See: #2527

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

drivers/gpio/gpiolib.c

@@ -50,6 +50,8 @@
  * GPIOs can sometimes cost only an instruction or two per bit.
  */
 
+#define dont_test_bit(b,d) (0)
+
 /* Device and char device-related information */
 static DEFINE_IDA(gpio_ida);
 static dev_t gpio_devt;
@@ -2745,8 +2747,8 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
 		value = !!value;
 
 	/* GPIOs used for enabled IRQs shall not be set as output */
-	if (test_bit(FLAG_USED_AS_IRQ, &flags) &&
-	    test_bit(FLAG_IRQ_IS_ENABLED, &flags)) {
+	if (dont_test_bit(FLAG_USED_AS_IRQ, &flags) &&
+	    dont_test_bit(FLAG_IRQ_IS_ENABLED, &flags)) {
 		gpiod_err(desc,
 			  "%s: tried to set a GPIO tied to an IRQ as output\n",
 			  __func__);
@@ -3657,8 +3659,8 @@ int gpiochip_lock_as_irq(struct gpio_chip *gc, unsigned int offset)
 	}
 
 	/* 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)) {
+	if (dont_test_bit(FLAG_IS_OUT, &desc->flags) &&
+	    !dont_test_bit(FLAG_OPEN_DRAIN, &desc->flags)) {
 		chip_err(gc,
 			 "%s: tried to flag a GPIO set as output for IRQ\n",
 			 __func__);