irqdomain: Handle domain hierarchy parent in irq_domain_instantiate()

To use irq_domain_instantiate() from irq_domain_create_hierarchy(),
irq_domain_instantiate() needs to handle the domain hierarchy parent.

Add the required functionality.
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240614173232.1184015-9-herve.codina@bootlin.com

include/linux/irqdomain.h

@@ -276,6 +276,12 @@ struct irq_domain_info {
 	int					direct_max;
 	const struct irq_domain_ops		*ops;
 	void					*host_data;
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+	/**
+	 * @parent: Pointer to the parent irq domain used in a hierarchy domain
+	 */
+	struct irq_domain			*parent;
+#endif
 };
 
 struct irq_domain *irq_domain_instantiate(const struct irq_domain_info *info);

kernel/irq/irqdomain.c

@@ -265,6 +265,13 @@ struct irq_domain *irq_domain_instantiate(const struct irq_domain_info *info)
 
 	domain->flags |= info->domain_flags;
 
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+	if (info->parent) {
+		domain->root = info->parent->root;
+		domain->parent = info->parent;
+	}
+#endif
+
 	__irq_domain_publish(domain);
 
 	return domain;