genirq: Prevent spurious detection for unconditionally polled interrupts

On a 68k platform a couple of interrupts are demultiplexed and
"polled" from a top level interrupt. Unfortunately there is no way to
determine which of the sub interrupts raised the top level interrupt,
so all of the demultiplexed interrupt handlers need to be
invoked. Given a high enough frequency this can trigger the spurious
interrupt detection mechanism, if one of the demultiplex interrupts
returns IRQ_NONE continuously. But this is a false positive as the
polling causes this behaviour and not buggy hardware/software.

Introduce IRQ_POLLED which can be set at interrupt chip setup time via
irq_set_status_flags(). The flag excludes the interrupt from the
spurious detector and from all core polling activities.

Reported-and-tested-by: Michael Schmitz <schmitzmic@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-m68k@vger.kernel.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1311061149250.23353@ionos.tec.linutronix.de

2 files changed, 16 insertions, 3 deletions

diff --git a/kernel/irq/settings.h b/kernel/irq/settings.h
index 1162f1030f18..3320b84cc60f 100644
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -14,6 +14,7 @@ enum {
         _IRQ_NO_BALANCING       = IRQ_NO_BALANCING,
         _IRQ_NESTED_THREAD      = IRQ_NESTED_THREAD,
         _IRQ_PER_CPU_DEVID      = IRQ_PER_CPU_DEVID,
+        _IRQ_IS_POLLED          = IRQ_IS_POLLED,
         _IRQF_MODIFY_MASK       = IRQF_MODIFY_MASK,
 };
 
@@ -26,6 +27,7 @@ enum {
 #define IRQ_NOAUTOEN            GOT_YOU_MORON
 #define IRQ_NESTED_THREAD       GOT_YOU_MORON
 #define IRQ_PER_CPU_DEVID       GOT_YOU_MORON
+#define IRQ_IS_POLLED           GOT_YOU_MORON
 #undef IRQF_MODIFY_MASK
 #define IRQF_MODIFY_MASK        GOT_YOU_MORON
 
@@ -147,3 +149,8 @@ static inline bool irq_settings_is_nested_thread(struct irq_desc *desc)
 {
         return desc->status_use_accessors & _IRQ_NESTED_THREAD;
 }
+
+static inline bool irq_settings_is_polled(struct irq_desc *desc)
+{
+        return desc->status_use_accessors & _IRQ_IS_POLLED;
+}
diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index 7b5f012bde9d..a1d8cc63b56e 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -67,8 +67,13 @@ static int try_one_irq(int irq, struct irq_desc *desc, bool force)
 
         raw_spin_lock(&desc->lock);
 
-        /* PER_CPU and nested thread interrupts are never polled */
-        if (irq_settings_is_per_cpu(desc) || irq_settings_is_nested_thread(desc))
+        /*
+         * PER_CPU, nested thread interrupts and interrupts explicitely
+         * marked polled are excluded from polling.
+         */
+        if (irq_settings_is_per_cpu(desc) ||
+            irq_settings_is_nested_thread(desc) ||
+            irq_settings_is_polled(desc))
                 goto out;
 
         /*
@@ -268,7 +273,8 @@ try_misrouted_irq(unsigned int irq, struct irq_desc *desc,
 void note_interrupt(unsigned int irq, struct irq_desc *desc,
                     irqreturn_t action_ret)
 {
-        if (desc->istate & IRQS_POLL_INPROGRESS)
+        if (desc->istate & IRQS_POLL_INPROGRESS ||
+            irq_settings_is_polled(desc))
                 return;
 
         /* we get here again via the threaded handler */