[PATCH 6/9] gpio: Add support for hierarchical IRQ domains

[Thierry Reding <thierry.reding@xxxxxxxxx>]

From: Thierry Reding <treding@xxxxxxxxxx>

Hierarchical IRQ domains can be used to stack different IRQ controllers
on top of each other. One specific use-case where this can be useful is
if a power management controller has top-level controls for wakeup
interrupts. In such cases, the power management controller can be a
parent to other interrupt controllers and program additional registers
when an IRQ has its wake capability enabled or disabled.

Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
 drivers/gpio/gpiolib.c      | 15 +++++++++++----
 include/linux/gpio/driver.h |  6 ++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index a53d17745d21..94146093ee95 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1918,7 +1918,9 @@ static int gpiochip_add_irqchip(struct gpio_chip *gpiochip,
 		type = IRQ_TYPE_NONE;
 	}
 
-	gpiochip->to_irq = gpiochip_to_irq;
+	if (!gpiochip->to_irq)
+		gpiochip->to_irq = gpiochip_to_irq;
+
 	gpiochip->irq.default_type = type;
 	gpiochip->irq.lock_key = lock_key;
 	gpiochip->irq.request_key = request_key;
@@ -1928,9 +1930,14 @@ static int gpiochip_add_irqchip(struct gpio_chip *gpiochip,
 	else
 		ops = &gpiochip_domain_ops;
 
-	gpiochip->irq.domain = irq_domain_add_simple(np, gpiochip->ngpio,
-						     gpiochip->irq.first,
-						     ops, gpiochip);
+	if (gpiochip->irq.parent_domain)
+		gpiochip->irq.domain = irq_domain_add_hierarchy(gpiochip->irq.parent_domain,
+								0, gpiochip->ngpio,
+								np, ops, gpiochip);
+	else
+		gpiochip->irq.domain = irq_domain_add_simple(np, gpiochip->ngpio,
+							     gpiochip->irq.first,
+							     ops, gpiochip);
 	if (!gpiochip->irq.domain)
 		return -EINVAL;
 
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index d8dcd0e44cab..fcd09a396d76 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -47,6 +47,12 @@ struct gpio_irq_chip {
 	 */
 	const struct irq_domain_ops *domain_ops;
 
+	/**
+	 * @parent_domain:
+	 *
+	 */
+	struct irq_domain *parent_domain;
+
 	/**
 	 * @handler:
 	 *
-- 
2.19.0