gpio: Introduce struct gpio_irq_chip.first

Some GPIO chips cannot support sparse IRQ numbering and therefore need
to manually allocate their interrupt descriptors statically. For these
cases, a driver can pass the first allocated IRQ via the struct
gpio_irq_chip's "first" field and thereby cause the IRQ domain to map
all IRQs during initialization.

Suggested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 389257f..6d5c366 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1778,7 +1778,8 @@ static int gpiochip_add_irqchip(struct gpio_chip *gpiochip)
 		ops = &gpiochip_domain_ops;
 
 	gpiochip->irq.domain = irq_domain_add_simple(np, gpiochip->ngpio,
-						     0, ops, gpiochip);
+						     gpiochip->irq.first,
+						     ops, gpiochip);
 	if (!gpiochip->irq.domain)
 		return -EINVAL;