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: NGrygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>
Acked-by: NGrygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

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;
 

include/linux/gpio/driver.h

@@ -128,6 +128,14 @@ struct gpio_irq_chip {
 	 * in IRQ domain of the chip.
 	 */
 	unsigned long *valid_mask;
+
+	/**
+	 * @first:
+	 *
+	 * Required for static IRQ allocation. If set, irq_domain_add_simple()
+	 * will allocate and map all IRQs during initialization.
+	 */
+	unsigned int first;
 };
 
 static inline struct gpio_irq_chip *to_gpio_irq_chip(struct irq_chip *chip)