[ARM] Fix Neponset IRQ handling

While testing the genirq code on ARM, a condition was found whereby
the Neponset IRQ handler was being re-entered, causing the system
to deadlock.

Under the ARM IRQ code, this would not have been a visible problem
because the "simple" IRQ handling had no re-entrancy protection.

Resolve this by acknowledging the parent interrupt after we mask it
when we are going to handle one of our "special" level-based sources
(from ethernet or USAR chip.)

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/arm/mach-sa1100/neponset.c b/arch/arm/mach-sa1100/neponset.c
index 9e02bc3712a0..af6d2775cf82 100644
--- a/arch/arm/mach-sa1100/neponset.c
+++ b/arch/arm/mach-sa1100/neponset.c
@@ -59,6 +59,14 @@ neponset_irq_handler(unsigned int irq, struct irqdesc *desc, struct pt_regs *reg
                 if (irr & (IRR_ETHERNET | IRR_USAR)) {
                         desc->chip->mask(irq);
 
+                        /*
+                         * Ack the interrupt now to prevent re-entering
+                         * this neponset handler.  Again, this is safe
+                         * since we'll check the IRR register prior to
+                         * leaving.
+                         */
+                        desc->chip->ack(irq);
+
                         if (irr & IRR_ETHERNET) {
                                 d = irq_desc + IRQ_NEPONSET_SMC9196;
                                 desc_handle_irq(IRQ_NEPONSET_SMC9196, d, regs);