From c891de13b385afb3e4b2c97ac5bbea7e2d97252f Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Fri, 4 Dec 2015 17:41:50 +0000
Subject: [PATCH 005/232] irq-bcm2836: Prevent spurious interrupts, and trap
 them early

The old arch-specific IRQ macros included a dsb to ensure the
write to clear the mailbox interrupt completed before returning
from the interrupt. The BCM2836 irqchip driver needs the same
precaution to avoid spurious interrupts.

Spurious interrupts are still possible for other reasons,
though, so trap them early.
---
 drivers/irqchip/irq-bcm2836.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/irqchip/irq-bcm2836.c
+++ b/drivers/irqchip/irq-bcm2836.c
@@ -170,9 +170,10 @@ __exception_irq_entry bcm2836_arm_irqchi
 		u32 ipi = ffs(mbox_val) - 1;
 
 		writel(1 << ipi, mailbox0);
+		dsb();
 		handle_IPI(ipi, regs);
 #endif
-	} else {
+	} else if (stat) {
 		u32 hwirq = ffs(stat) - 1;
 
 		handle_IRQ(irq_linear_revmap(intc.domain, hwirq), regs);