[PATCH v3 1/5] irq: Add CONFIG_GENERIC_IRQ_MULTI_HANDLER

[Palmer Dabbelt <palmer@sifive.com>]

It looks like the arm irqchip registration mechanism has been copied
into a handful of ports, including arm64 and openrisc.  I want to use
this in the RISC-V port, so I thought it would be good to make this
generic instead.

This patch copies the arm definition of CONFIG_MULTI_IRQ_HANDLER into
kernel/irq under CONFIG_GENERIC_MULTI_IRQ_HANDLER.  This patch is
currently all dead code, but it will be enabled in the various other
architectures in subsequent patches.

Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
---
 include/linux/irq.h | 18 ++++++++++++++++++
 kernel/irq/Kconfig  |  5 +++++
 kernel/irq/handle.c | 15 +++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index a0231e96a578..77e97872a13e 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -1170,4 +1170,22 @@ int __ipi_send_mask(struct irq_desc *desc, const struct cpumask *dest);
 int ipi_send_single(unsigned int virq, unsigned int cpu);
 int ipi_send_mask(unsigned int virq, const struct cpumask *dest);
 
+#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
+/*
+ * Registers a generic IRQ handling function as the top-level IRQ handler in
+ * the system, which is generally the first C code called from an assembly
+ * architecture-specific interrupt handler.
+ *
+ * Returns 0 on success, or -EBUSY if an IRQ handler has already been
+ * registered.
+ */
+int __init set_handle_irq(void (*handle_irq)(struct pt_regs *));
+
+/*
+ * Allows interrupt handlers to find the irqchip that's been registered as the
+ * top-level IRQ handler.
+ */
+extern void (*handle_arch_irq)(struct pt_regs *) __ro_after_init;
+#endif
+
 #endif /* _LINUX_IRQ_H */
diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index 6fc87ccda1d7..116a6972f124 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -132,3 +132,8 @@ config GENERIC_IRQ_DEBUGFS
 	  If you don't know what to do here, say N.
 
 endmenu
+
+config GENERIC_IRQ_MULTI_HANDLER
+	bool
+	help
+	  Allow each machine to specify it's own IRQ handler at run time.
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 79f987b942b8..3570c715c3e7 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -20,6 +20,10 @@
 
 #include "internals.h"
 
+#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
+void (*handle_arch_irq)(struct pt_regs *) __ro_after_init;
+#endif
+
 /**
  * handle_bad_irq - handle spurious and unhandled irqs
  * @desc:      description of the interrupt
@@ -207,3 +211,14 @@ irqreturn_t handle_irq_event(struct irq_desc *desc)
 	irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
 	return ret;
 }
+
+#ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
+int __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
+{
+	if (handle_arch_irq)
+		return -EBUSY;
+
+	handle_arch_irq = handle_irq;
+	return 0;
+}
+#endif
-- 
2.16.1