irq_domain: Add support for base irq and hwirq in legacy mappings

Add support for a legacy mapping where irq = (hwirq - first_hwirq + first_irq)
so that a controller driver can allocate a fixed range of irq_descs and use
a simple calculation to translate back and forth between linux and hw irq
numbers. This is needed to use an irq_domain with many of the ARM interrupt
controller drivers that manage their own irq_desc allocations. Ultimately
the goal is to migrate those drivers to use the linear revmap, but doing it
this way allows each driver to be converted separately which makes the
migration path easier.

This patch generalizes the IRQ_DOMAIN_MAP_LEGACY method to use
(first_irq-first_hwirq) as the offset between hwirq and linux irq number,
and adds checks to make sure that the hwirq number does not exceed range
assigned to the controller.

Signed-off-by: Grant Likely <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Milton Miller <[e-mail]>
Tested-by: Olof Johansson <[e-mail]>

arch/powerpc/include/asm/irq.h

···
 /* Total number of virq in the platform */
 #define NR_IRQS		CONFIG_NR_IRQS
 
-/* Number of irqs reserved for the legacy controller */
-#define NUM_ISA_INTERRUPTS	16
-
 /* Same thing, used by the generic IRQ code */
 #define NR_IRQS_LEGACY		NUM_ISA_INTERRUPTS
 

arch/powerpc/sysdev/i8259.c

···
 	raw_spin_unlock_irqrestore(&i8259_lock, flags);
 
 	/* create a legacy host */
-	i8259_host = irq_domain_add_legacy(node, &i8259_host_ops, NULL);
+	i8259_host = irq_domain_add_legacy_isa(node, &i8259_host_ops, NULL);
 	if (i8259_host == NULL) {
 		printk(KERN_ERR "i8259: failed to allocate irq host !\n");
 		return;

arch/powerpc/sysdev/tsi108_pci.c

···
 {
 	DBG("Tsi108_pci_int_init: initializing PCI interrupts\n");
 
-	pci_irq_host = irq_domain_add_legacy(node, &pci_irq_domain_ops, NULL);
+	pci_irq_host = irq_domain_add_legacy_isa(node, &pci_irq_domain_ops, NULL);
 	if (pci_irq_host == NULL) {
 		printk(KERN_ERR "pci_irq_host: failed to allocate irq domain!\n");
 		return;

include/linux/irqdomain.h

···
 struct irq_domain;
 struct of_device_id;
 
+/* Number of irqs reserved for a legacy isa controller */
+#define NUM_ISA_INTERRUPTS	16
+
 /* This type is the placeholder for a hardware interrupt number. It has to
  * be big enough to enclose whatever representation is used by a given
  * platform.
···
 	union {
 		struct {
 			unsigned int size;
+			unsigned int first_irq;
+			irq_hw_number_t first_hwirq;
+		} legacy;
+		struct {
+			unsigned int size;
 			unsigned int *revmap;
 		} linear;
 		struct radix_tree_root tree;
···
 #ifdef CONFIG_IRQ_DOMAIN
 #ifdef CONFIG_PPC
 struct irq_domain *irq_domain_add_legacy(struct device_node *of_node,
+					 unsigned int size,
+					 unsigned int first_irq,
+					 irq_hw_number_t first_hwirq,
 					 struct irq_domain_ops *ops,
 					 void *host_data);
 struct irq_domain *irq_domain_add_linear(struct device_node *of_node,
···
 					 struct irq_domain_ops *ops,
 					 void *host_data);
 
-
 extern struct irq_domain *irq_find_host(struct device_node *node);
 extern void irq_set_default_host(struct irq_domain *host);
 extern void irq_set_virq_count(unsigned int count);
 
+static inline struct irq_domain *irq_domain_add_legacy_isa(
+				struct device_node *of_node,
+				struct irq_domain_ops *ops,
+				void *host_data)
+{
+	return irq_domain_add_legacy(of_node, NUM_ISA_INTERRUPTS, 0, 0, ops,
+				     host_data);
+}
 
 extern unsigned int irq_create_mapping(struct irq_domain *host,
 				       irq_hw_number_t hwirq);

kernel/irq/irqdomain.c

···
 #include <linux/smp.h>
 #include <linux/fs.h>
 
-#define IRQ_DOMAIN_MAP_LEGACY 0 /* legacy 8259, gets irqs 1..15 */
+#define IRQ_DOMAIN_MAP_LEGACY 0 /* driver allocated fixed range of irqs.
+				 * ie. legacy 8259, gets irqs 1..15 */
 #define IRQ_DOMAIN_MAP_NOMAP 1 /* no fast reverse mapping */
 #define IRQ_DOMAIN_MAP_LINEAR 2 /* linear map of interrupts */
 #define IRQ_DOMAIN_MAP_TREE 3 /* radix tree */
···
 		 domain->revmap_type, domain);
 }
 
+static unsigned int irq_domain_legacy_revmap(struct irq_domain *domain,
+					     irq_hw_number_t hwirq)
+{
+	irq_hw_number_t first_hwirq = domain->revmap_data.legacy.first_hwirq;
+	int size = domain->revmap_data.legacy.size;
+
+	if (WARN_ON(hwirq < first_hwirq || hwirq >= first_hwirq + size))
+		return 0;
+	return hwirq - first_hwirq + domain->revmap_data.legacy.first_irq;
+}
+
 /**
  * irq_domain_add_legacy() - Allocate and register a legacy revmap irq_domain.
  * @of_node: pointer to interrupt controller's device tree node.
+ * @size: total number of irqs in legacy mapping
+ * @first_irq: first number of irq block assigned to the domain
+ * @first_hwirq: first hwirq number to use for the translation. Should normally
+ *               be '0', but a positive integer can be used if the effective
+ *               hwirqs numbering does not begin at zero.
  * @ops: map/unmap domain callbacks
  * @host_data: Controller private data pointer
  *
···
  * a legacy controller).
  */
 struct irq_domain *irq_domain_add_legacy(struct device_node *of_node,
+					 unsigned int size,
+					 unsigned int first_irq,
+					 irq_hw_number_t first_hwirq,
 					 struct irq_domain_ops *ops,
 					 void *host_data)
 {
-	struct irq_domain *domain, *h;
+	struct irq_domain *domain;
 	unsigned int i;
 
 	domain = irq_domain_alloc(of_node, IRQ_DOMAIN_MAP_LEGACY, ops, host_data);
 	if (!domain)
 		return NULL;
 
+	domain->revmap_data.legacy.first_irq = first_irq;
+	domain->revmap_data.legacy.first_hwirq = first_hwirq;
+	domain->revmap_data.legacy.size = size;
+
 	mutex_lock(&irq_domain_mutex);
-	/* Make sure only one legacy controller can be created */
-	list_for_each_entry(h, &irq_domain_list, link) {
-		if (WARN_ON(h->revmap_type == IRQ_DOMAIN_MAP_LEGACY)) {
+	/* Verify that all the irqs are available */
+	for (i = 0; i < size; i++) {
+		int irq = first_irq + i;
+		struct irq_data *irq_data = irq_get_irq_data(irq);
+
+		if (WARN_ON(!irq_data || irq_data->domain)) {
 			mutex_unlock(&irq_domain_mutex);
 			of_node_put(domain->of_node);
 			kfree(domain);
 			return NULL;
 		}
 	}
-	list_add(&domain->link, &irq_domain_list);
+
+	/* Claim all of the irqs before registering a legacy domain */
+	for (i = 0; i < size; i++) {
+		struct irq_data *irq_data = irq_get_irq_data(first_irq + i);
+		irq_data->hwirq = first_hwirq + i;
+		irq_data->domain = domain;
+	}
 	mutex_unlock(&irq_domain_mutex);
 
-	/* setup us as the domain for all legacy interrupts */
-	for (i = 1; i < NUM_ISA_INTERRUPTS; i++) {
-		struct irq_data *irq_data = irq_get_irq_data(i);
-		irq_data->hwirq = i;
-		irq_data->domain = domain;
+	for (i = 0; i < size; i++) {
+		int irq = first_irq + i;
+		int hwirq = first_hwirq + i;
+
+		/* IRQ0 gets ignored */
+		if (!irq)
+			continue;
 
 		/* Legacy flags are left to default at this point,
 		 * one can then use irq_create_mapping() to
 		 * explicitly change them
 		 */
-		ops->map(domain, i, i);
+		ops->map(domain, irq, hwirq);
 
 		/* Clear norequest flags */
-		irq_clear_status_flags(i, IRQ_NOREQUEST);
+		irq_clear_status_flags(irq, IRQ_NOREQUEST);
 	}
+
+	irq_domain_add(domain);
 	return domain;
 }
 
···
 	}
 
 	/* Get a virtual interrupt number */
-	if (domain->revmap_type == IRQ_DOMAIN_MAP_LEGACY) {
-		/* Handle legacy */
-		virq = (unsigned int)hwirq;
-		if (virq == 0 || virq >= NUM_ISA_INTERRUPTS)
-			return 0;
-		return virq;
-	} else {
-		/* Allocate a virtual interrupt number */
-		hint = hwirq % irq_virq_count;
-		if (hint == 0)
-			hint++;
-		virq = irq_alloc_desc_from(hint, 0);
-		if (!virq)
-			virq = irq_alloc_desc_from(1, 0);
-		if (!virq) {
-			pr_debug("irq: -> virq allocation failed\n");
-			return 0;
-		}
+	if (domain->revmap_type == IRQ_DOMAIN_MAP_LEGACY)
+		return irq_domain_legacy_revmap(domain, hwirq);
+
+	/* Allocate a virtual interrupt number */
+	hint = hwirq % irq_virq_count;
+	if (hint == 0)
+		hint++;
+	virq = irq_alloc_desc_from(hint, 0);
+	if (!virq)
+		virq = irq_alloc_desc_from(1, 0);
+	if (!virq) {
+		pr_debug("irq: -> virq allocation failed\n");
+		return 0;
 	}
 
 	if (irq_setup_virq(domain, virq, hwirq)) {
···
 
 	/* legacy -> bail early */
 	if (domain->revmap_type == IRQ_DOMAIN_MAP_LEGACY)
-		return hwirq;
+		return irq_domain_legacy_revmap(domain, hwirq);
 
 	/* Slow path does a linear search of the map */
 	if (hint == 0)