irqdomain: Add irq_domain_{push,pop}_irq() functions

For an already existing irqdomain hierarchy, as might be obtained via
a call to pci_enable_msix_range(), a PCI driver wishing to add an
additional irqdomain to the hierarchy needs to be able to insert the
irqdomain to that already initialized hierarchy.  Calling
irq_domain_create_hierarchy() allows the new irqdomain to be created,
but no existing code allows for initializing the associated irq_data.

Add a couple of helper functions (irq_domain_push_irq() and
irq_domain_pop_irq()) to initialize the irq_data for the new
irqdomain added to an existing hierarchy.

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Link: http://lkml.kernel.org/r/1503017616-3252-6-git-send-email-david.daney@cavium.com

include/linux/irqdomain.h

@@ -460,6 +460,9 @@ extern void irq_domain_free_irqs_common(struct irq_domain *domain,
 extern void irq_domain_free_irqs_top(struct irq_domain *domain,
 				     unsigned int virq, unsigned int nr_irqs);
 
+extern int irq_domain_push_irq(struct irq_domain *domain, int virq, void *arg);
+extern int irq_domain_pop_irq(struct irq_domain *domain, int virq);
+
 extern int irq_domain_alloc_irqs_parent(struct irq_domain *domain,
 					unsigned int irq_base,
 					unsigned int nr_irqs, void *arg);

kernel/irq/irqdomain.c

@@ -1449,6 +1449,175 @@ int __irq_domain_alloc_irqs(struct irq_domain *domain, int irq_base,
 	return ret;
 }
 
+/* The irq_data was moved, fix the revmap to refer to the new location */
+static void irq_domain_fix_revmap(struct irq_data *d)
+{
+	void **slot;
+
+	if (d->hwirq < d->domain->revmap_size)
+		return; /* Not using radix tree. */
+
+	/* Fix up the revmap. */
+	mutex_lock(&revmap_trees_mutex);
+	slot = radix_tree_lookup_slot(&d->domain->revmap_tree, d->hwirq);
+	if (slot)
+		radix_tree_replace_slot(&d->domain->revmap_tree, slot, d);
+	mutex_unlock(&revmap_trees_mutex);
+}
+
+/**
+ * irq_domain_push_irq() - Push a domain in to the top of a hierarchy.
+ * @domain:	Domain to push.
+ * @virq:	Irq to push the domain in to.
+ * @arg:	Passed to the irq_domain_ops alloc() function.
+ *
+ * For an already existing irqdomain hierarchy, as might be obtained
+ * via a call to pci_enable_msix(), add an additional domain to the
+ * head of the processing chain.  Must be called before request_irq()
+ * has been called.
+ */
+int irq_domain_push_irq(struct irq_domain *domain, int virq, void *arg)
+{
+	struct irq_data *child_irq_data;
+	struct irq_data *root_irq_data = irq_get_irq_data(virq);
+	struct irq_desc *desc;
+	int rv = 0;
+
+	/*
+	 * Check that no action has been set, which indicates the virq
+	 * is in a state where this function doesn't have to deal with
+	 * races between interrupt handling and maintaining the
+	 * hierarchy.  This will catch gross misuse.  Attempting to
+	 * make the check race free would require holding locks across
+	 * calls to struct irq_domain_ops->alloc(), which could lead
+	 * to deadlock, so we just do a simple check before starting.
+	 */
+	desc = irq_to_desc(virq);
+	if (!desc)
+		return -EINVAL;
+	if (WARN_ON(desc->action))
+		return -EBUSY;
+
+	if (domain == NULL)
+		return -EINVAL;
+
+	if (WARN_ON(!irq_domain_is_hierarchy(domain)))
+		return -EINVAL;
+
+	if (domain->parent != root_irq_data->domain)
+		return -EINVAL;
+
+	if (!root_irq_data)
+		return -EINVAL;
+
+	child_irq_data = kzalloc_node(sizeof(*child_irq_data), GFP_KERNEL,
+				      irq_data_get_node(root_irq_data));
+	if (!child_irq_data)
+		return -ENOMEM;
+
+	mutex_lock(&irq_domain_mutex);
+
+	/* Copy the original irq_data. */
+	*child_irq_data = *root_irq_data;
+
+	/*
+	 * Overwrite the root_irq_data, which is embedded in struct
+	 * irq_desc, with values for this domain.
+	 */
+	root_irq_data->parent_data = child_irq_data;
+	root_irq_data->domain = domain;
+	root_irq_data->mask = 0;
+	root_irq_data->hwirq = 0;
+	root_irq_data->chip = NULL;
+	root_irq_data->chip_data = NULL;
+
+	/* May (probably does) set hwirq, chip, etc. */
+	rv = irq_domain_alloc_irqs_hierarchy(domain, virq, 1, arg);
+	if (rv) {
+		/* Restore the original irq_data. */
+		*root_irq_data = *child_irq_data;
+		goto error;
+	}
+
+	irq_domain_fix_revmap(child_irq_data);
+	irq_domain_set_mapping(domain, root_irq_data->hwirq, root_irq_data);
+
+error:
+	mutex_unlock(&irq_domain_mutex);
+
+	return rv;
+}
+EXPORT_SYMBOL_GPL(irq_domain_push_irq);
+
+/**
+ * irq_domain_pop_irq() - Remove a domain from the top of a hierarchy.
+ * @domain:	Domain to remove.
+ * @virq:	Irq to remove the domain from.
+ *
+ * Undo the effects of a call to irq_domain_push_irq().  Must be
+ * called either before request_irq() or after free_irq().
+ */
+int irq_domain_pop_irq(struct irq_domain *domain, int virq)
+{
+	struct irq_data *root_irq_data = irq_get_irq_data(virq);
+	struct irq_data *child_irq_data;
+	struct irq_data *tmp_irq_data;
+	struct irq_desc *desc;
+
+	/*
+	 * Check that no action is set, which indicates the virq is in
+	 * a state where this function doesn't have to deal with races
+	 * between interrupt handling and maintaining the hierarchy.
+	 * This will catch gross misuse.  Attempting to make the check
+	 * race free would require holding locks across calls to
+	 * struct irq_domain_ops->free(), which could lead to
+	 * deadlock, so we just do a simple check before starting.
+	 */
+	desc = irq_to_desc(virq);
+	if (!desc)
+		return -EINVAL;
+	if (WARN_ON(desc->action))
+		return -EBUSY;
+
+	if (domain == NULL)
+		return -EINVAL;
+
+	if (!root_irq_data)
+		return -EINVAL;
+
+	tmp_irq_data = irq_domain_get_irq_data(domain, virq);
+
+	/* We can only "pop" if this domain is at the top of the list */
+	if (WARN_ON(root_irq_data != tmp_irq_data))
+		return -EINVAL;
+
+	if (WARN_ON(root_irq_data->domain != domain))
+		return -EINVAL;
+
+	child_irq_data = root_irq_data->parent_data;
+	if (WARN_ON(!child_irq_data))
+		return -EINVAL;
+
+	mutex_lock(&irq_domain_mutex);
+
+	root_irq_data->parent_data = NULL;
+
+	irq_domain_clear_mapping(domain, root_irq_data->hwirq);
+	irq_domain_free_irqs_hierarchy(domain, virq, 1);
+
+	/* Restore the original irq_data. */
+	*root_irq_data = *child_irq_data;
+
+	irq_domain_fix_revmap(root_irq_data);
+
+	mutex_unlock(&irq_domain_mutex);
+
+	kfree(child_irq_data);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(irq_domain_pop_irq);
+
 /**
  * irq_domain_free_irqs - Free IRQ number and associated data structures
  * @virq:	base IRQ number