[PATCH 2/3] irq_domain: eliminate slow-path revmap lookups

[Grant Likely <grant.likely@secretlab.ca>]

With the current state of irq_domain, the reverse map is always updated
when new IRQs get mapped.  This means that the irq_find_mapping() function
can be simplified to always execute the revmap-specific lookup function.

This patch adds lookup functions for the revmaps that don't yet have one
and removes the slow path lookup code path.

v6: Remove the slow path entirely.  The only place where the slow path
    could get called is for a linear mapping if the hwirq number is larger
    than the linear revmap size.
v5: rewrite to not use a ->revmap() callback.  It is simpler, smaller,
    safer and faster to open code each of the revmap lookups directly into
    irq_find_mapping() via a switch statement.
v4: Fix build failure on incorrect variable reference.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Milton Miller <miltonm@bga.com>
---
 arch/powerpc/sysdev/xics/icp-hv.c      |    2 +-
 arch/powerpc/sysdev/xics/icp-native.c  |    2 +-
 arch/powerpc/sysdev/xics/xics-common.c |    3 -
 include/linux/irqdomain.h              |    4 -
 kernel/irq/irqdomain.c                 |  129 ++++++++++----------------------
 5 files changed, 43 insertions(+), 97 deletions(-)

diff --git a/arch/powerpc/sysdev/xics/icp-hv.c b/arch/powerpc/sysdev/xics/icp-hv.c
index 253dce9..14469cf 100644
--- a/arch/powerpc/sysdev/xics/icp-hv.c
+++ b/arch/powerpc/sysdev/xics/icp-hv.c
@@ -111,7 +111,7 @@ static unsigned int icp_hv_get_irq(void)
 	if (vec == XICS_IRQ_SPURIOUS)
 		return NO_IRQ;
 
-	irq = irq_radix_revmap_lookup(xics_host, vec);
+	irq = irq_find_mapping(xics_host, vec);
 	if (likely(irq != NO_IRQ)) {
 		xics_push_cppr(vec);
 		return irq;
diff --git a/arch/powerpc/sysdev/xics/icp-native.c b/arch/powerpc/sysdev/xics/icp-native.c
index 4c79b6f..48861d3 100644
--- a/arch/powerpc/sysdev/xics/icp-native.c
+++ b/arch/powerpc/sysdev/xics/icp-native.c
@@ -119,7 +119,7 @@ static unsigned int icp_native_get_irq(void)
 	if (vec == XICS_IRQ_SPURIOUS)
 		return NO_IRQ;
 
-	irq = irq_radix_revmap_lookup(xics_host, vec);
+	irq = irq_find_mapping(xics_host, vec);
 	if (likely(irq != NO_IRQ)) {
 		xics_push_cppr(vec);
 		return irq;
diff --git a/arch/powerpc/sysdev/xics/xics-common.c b/arch/powerpc/sysdev/xics/xics-common.c
index ea5e204..1d7067d 100644
--- a/arch/powerpc/sysdev/xics/xics-common.c
+++ b/arch/powerpc/sysdev/xics/xics-common.c
@@ -330,9 +330,6 @@ static int xics_host_map(struct irq_domain *h, unsigned int virq,
 
 	pr_devel("xics: map virq %d, hwirq 0x%lx\n", virq, hw);
 
-	/* Insert the interrupt mapping into the radix tree for fast lookup */
-	irq_radix_revmap_insert(xics_host, virq, hw);
-
 	/* They aren't all level sensitive but we just don't really know */
 	irq_set_status_flags(virq, IRQ_LEVEL);
 
diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
index ac17b9b..7a7af17 100644
--- a/include/linux/irqdomain.h
+++ b/include/linux/irqdomain.h
@@ -149,10 +149,6 @@ extern void irq_dispose_mapping(unsigned int virq);
 extern unsigned int irq_find_mapping(struct irq_domain *host,
 				     irq_hw_number_t hwirq);
 extern unsigned int irq_create_direct_mapping(struct irq_domain *host);
-extern void irq_radix_revmap_insert(struct irq_domain *host, unsigned int virq,
-				    irq_hw_number_t hwirq);
-extern unsigned int irq_radix_revmap_lookup(struct irq_domain *host,
-					    irq_hw_number_t hwirq);
 extern unsigned int irq_linear_revmap(struct irq_domain *host,
 				      irq_hw_number_t hwirq);
 
diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 041710d..df92a34 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -314,7 +314,8 @@ unsigned int irq_create_direct_mapping(struct irq_domain *domain)
 		domain = irq_default_domain;
 
 	BUG_ON(domain == NULL);
-	WARN_ON(domain->revmap_type != IRQ_DOMAIN_MAP_NOMAP);
+	if (WARN_ON(domain->revmap_type != IRQ_DOMAIN_MAP_NOMAP))
+		return 0;
 
 	virq = irq_alloc_desc_from(1, 0);
 	if (!virq) {
@@ -385,11 +386,22 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
 	}
 
 	if (irq_setup_virq(domain, virq, hwirq)) {
-		if (domain->revmap_type != IRQ_DOMAIN_MAP_LEGACY)
-			irq_free_desc(virq);
+		irq_free_desc(virq);
 		return 0;
 	}
 
+	switch(domain->revmap_type) {
+	case IRQ_DOMAIN_MAP_LINEAR:
+		if (hwirq < domain->revmap_data.linear.size)
+			domain->revmap_data.linear.revmap[hwirq] = virq;
+		break;
+	case IRQ_DOMAIN_MAP_TREE:
+		mutex_lock(&revmap_trees_mutex);
+		radix_tree_insert(&domain->revmap_data.tree, hwirq,
+				  irq_get_irq_data(virq));
+		mutex_unlock(&revmap_trees_mutex);
+		break;
+	}
 	pr_debug("irq: irq %lu on domain %s mapped to virtual irq %u\n",
 		hwirq, domain->of_node ? domain->of_node->full_name : "null", virq);
 
@@ -510,8 +522,7 @@ EXPORT_SYMBOL_GPL(irq_dispose_mapping);
 unsigned int irq_find_mapping(struct irq_domain *domain,
 			      irq_hw_number_t hwirq)
 {
-	unsigned int i;
-	struct irq_desc *desc;
+	struct irq_data *data;
 
 	/* Look for default domain if nececssary */
 	if (domain == NULL)
@@ -519,107 +530,49 @@ unsigned int irq_find_mapping(struct irq_domain *domain,
 	if (domain == NULL)
 		return 0;
 
-	/* legacy -> bail early */
-	if (domain->revmap_type == IRQ_DOMAIN_MAP_LEGACY)
+	switch (domain->revmap_type) {
+	case IRQ_DOMAIN_MAP_LEGACY:
 		return irq_domain_legacy_revmap(domain, hwirq);
-
-	/* Slow path does a linear search of the map */
-	for_each_irq_desc(i, desc)  {
-		struct irq_data *data = irq_get_irq_data(i);
+	case IRQ_DOMAIN_MAP_LINEAR:
+		return irq_linear_revmap(domain, hwirq);
+	case IRQ_DOMAIN_MAP_TREE:
+		rcu_read_lock();
+		data = radix_tree_lookup(&domain->revmap_data.tree, hwirq);
+		rcu_read_unlock();
+		if (data)
+			return data->irq;
+		break;
+	case IRQ_DOMAIN_MAP_NOMAP:
+		data = irq_get_irq_data(hwirq);
 		if (data && (data->domain == domain) && (data->hwirq == hwirq))
-			return i;
+			return hwirq;
+		break;
 	}
+
+	WARN(1, "ERROR: irq revmap went horribly wrong. revmap_type=%i\n",
+		domain->revmap_type);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(irq_find_mapping);
 
 /**
- * irq_radix_revmap_lookup() - Find a linux irq from a hw irq number.
- * @domain: domain owning this hardware interrupt
- * @hwirq: hardware irq number in that domain space
- *
- * This is a fast path, for use by irq controller code that uses radix tree
- * revmaps
- */
-unsigned int irq_radix_revmap_lookup(struct irq_domain *domain,
-				     irq_hw_number_t hwirq)
-{
-	struct irq_data *irq_data;
-
-	if (WARN_ON_ONCE(domain->revmap_type != IRQ_DOMAIN_MAP_TREE))
-		return irq_find_mapping(domain, hwirq);
-
-	/*
-	 * Freeing an irq can delete nodes along the path to
-	 * do the lookup via call_rcu.
-	 */
-	rcu_read_lock();
-	irq_data = radix_tree_lookup(&domain->revmap_data.tree, hwirq);
-	rcu_read_unlock();
-
-	/*
-	 * If found in radix tree, then fine.
-	 * Else fallback to linear lookup - this should not happen in practice
-	 * as it means that we failed to insert the node in the radix tree.
-	 */
-	return irq_data ? irq_data->irq : irq_find_mapping(domain, hwirq);
-}
-
-/**
- * irq_radix_revmap_insert() - Insert a hw irq to linux irq number mapping.
- * @domain: domain owning this hardware interrupt
- * @virq: linux irq number
- * @hwirq: hardware irq number in that domain space
- *
- * This is for use by irq controllers that use a radix tree reverse
- * mapping for fast lookup.
- */
-void irq_radix_revmap_insert(struct irq_domain *domain, unsigned int virq,
-			     irq_hw_number_t hwirq)
-{
-	struct irq_data *irq_data = irq_get_irq_data(virq);
-
-	if (WARN_ON(domain->revmap_type != IRQ_DOMAIN_MAP_TREE))
-		return;
-
-	if (virq) {
-		mutex_lock(&revmap_trees_mutex);
-		radix_tree_insert(&domain->revmap_data.tree, hwirq, irq_data);
-		mutex_unlock(&revmap_trees_mutex);
-	}
-}
-
-/**
  * irq_linear_revmap() - Find a linux irq from a hw irq number.
  * @domain: domain owning this hardware interrupt
  * @hwirq: hardware irq number in that domain space
  *
- * This is a fast path, for use by irq controller code that uses linear
- * revmaps. It does fallback to the slow path if the revmap doesn't exist
- * yet and will create the revmap entry with appropriate locking
+ * This is a fast path that can be called directly by irq controller code to
+ * save a handful of instructions.
  */
 unsigned int irq_linear_revmap(struct irq_domain *domain,
 			       irq_hw_number_t hwirq)
 {
-	unsigned int *revmap;
-
-	if (WARN_ON_ONCE(domain->revmap_type != IRQ_DOMAIN_MAP_LINEAR))
-		return irq_find_mapping(domain, hwirq);
+	BUG_ON(domain->revmap_type != IRQ_DOMAIN_MAP_LINEAR);
 
-	/* Check revmap bounds */
-	if (unlikely(hwirq >= domain->revmap_data.linear.size))
-		return irq_find_mapping(domain, hwirq);
-
-	/* Check if revmap was allocated */
-	revmap = domain->revmap_data.linear.revmap;
-	if (unlikely(revmap == NULL))
-		return irq_find_mapping(domain, hwirq);
-
-	/* Fill up revmap with slow path if no mapping found */
-	if (unlikely(!revmap[hwirq]))
-		revmap[hwirq] = irq_find_mapping(domain, hwirq);
+	/* Check revmap bounds; complain if exceeded */
+	if (WARN_ON(hwirq >= domain->revmap_data.linear.size))
+		return 0;
 
-	return revmap[hwirq];
+	return domain->revmap_data.linear.revmap[hwirq];
 }
 
 #ifdef CONFIG_IRQ_DOMAIN_DEBUG
-- 
1.7.9.1