gpio: flush direction status in gpiochip_lock_as_irq()

As irqchip and gpiochip functions are orthogonal, the IRQ
set-up or something else can have changed the direction of
the GPIO line from what the GPIO descriptor knows when we
get into gpiochip_lock_as_irq(). Make sure to re-read the
direction setting if we have the .get_direction() callback
enabled for the chip.

Else we get problems like this:

iio iio:device2: interrupts on the rising edge
gpio gpiochip2: (8012e080.gpio): gpiochip_lock_as_irq:
  tried to flag a GPIO set as output for IRQ
gpio gpiochip2: (8012e080.gpio): unable to lock HW IRQ 0 for IRQ
genirq: Failed to request resources for l3g4200d-trigger
  (irq 111) on irqchip nmk1-32-63
iio iio:device2: failed to request trigger IRQ.
st-gyro-i2c: probe of 2-0068 failed with error -22

Fixes: 72d320006177 ("gpio: set up initial state from .get_direction()")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -2066,17 +2066,30 @@ EXPORT_SYMBOL_GPL(gpiod_to_irq);
  */
 int gpiochip_lock_as_irq(struct gpio_chip *chip, unsigned int offset)
 {
-	if (offset >= chip->ngpio)
-		return -EINVAL;
+	struct gpio_desc *desc;
+
+	desc = gpiochip_get_desc(chip, offset);
+	if (IS_ERR(desc))
+		return PTR_ERR(desc);
+
+	/* Flush direction if something changed behind our back */
+	if (chip->get_direction) {
+		int dir = chip->get_direction(chip, offset);
+
+		if (dir)
+			clear_bit(FLAG_IS_OUT, &desc->flags);
+		else
+			set_bit(FLAG_IS_OUT, &desc->flags);
+	}
 
-	if (test_bit(FLAG_IS_OUT, &chip->gpiodev->descs[offset].flags)) {
+	if (test_bit(FLAG_IS_OUT, &desc->flags)) {
 		chip_err(chip,
 			  "%s: tried to flag a GPIO set as output for IRQ\n",
 			  __func__);
 		return -EIO;
 	}
 
-	set_bit(FLAG_USED_AS_IRQ, &chip->gpiodev->descs[offset].flags);
+	set_bit(FLAG_USED_AS_IRQ, &desc->flags);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiochip_lock_as_irq);