gpio: ixp4xx: Make irqchip immutable

This turns the IXP4xx GPIO irqchip into an immutable
irqchip, a bit different from the standard template due
to being hierarchical.

Tested on the IXP4xx which uses drivers/ata/pata_ixp4xx_cf.c
for a rootfs on compact flash with IRQs from this GPIO
block to the CF ATA controller.

Cc: Marc Zyngier <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Acked-by: Marc Zyngier <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-ixp4xx.c

···
 	__raw_writel(BIT(d->hwirq), g->base + IXP4XX_REG_GPIS);
 }
 
+static void ixp4xx_gpio_mask_irq(struct irq_data *d)
+{
+	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
+
+	irq_chip_mask_parent(d);
+	gpiochip_disable_irq(gc, d->hwirq);
+}
+
 static void ixp4xx_gpio_irq_unmask(struct irq_data *d)
 {
 	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
···
 	if (!(g->irq_edge & BIT(d->hwirq)))
 		ixp4xx_gpio_irq_ack(d);
 
+	gpiochip_enable_irq(gc, d->hwirq);
 	irq_chip_unmask_parent(d);
 }
 
···
 	return irq_chip_set_type_parent(d, IRQ_TYPE_LEVEL_HIGH);
 }
 
-static struct irq_chip ixp4xx_gpio_irqchip = {
+static const struct irq_chip ixp4xx_gpio_irqchip = {
 	.name = "IXP4GPIO",
 	.irq_ack = ixp4xx_gpio_irq_ack,
-	.irq_mask = irq_chip_mask_parent,
+	.irq_mask = ixp4xx_gpio_mask_irq,
 	.irq_unmask = ixp4xx_gpio_irq_unmask,
 	.irq_set_type = ixp4xx_gpio_irq_set_type,
+	.flags = IRQCHIP_IMMUTABLE,
+	GPIOCHIP_IRQ_RESOURCE_HELPERS,
 };
 
 static int ixp4xx_gpio_child_to_parent_hwirq(struct gpio_chip *gc,
···
 	g->gc.owner = THIS_MODULE;
 
 	girq = &g->gc.irq;
-	girq->chip = &ixp4xx_gpio_irqchip;
+	gpio_irq_chip_set_chip(girq, &ixp4xx_gpio_irqchip);
 	girq->fwnode = g->fwnode;
 	girq->parent_domain = parent;
 	girq->child_to_parent_hwirq = ixp4xx_gpio_child_to_parent_hwirq;