[PATCH 02/11] m68k/irq: Add handle_polled_irq() for timer based soft interrupts

[Michael Schmitz <schmitzmic@gmail.com>]

Experimental hack to avoid unhandled interrupt timer to fire
on EtherNEC/NetUSBee cards that have no hardware interrupt
and need to be polled from a timer interrupt.

This patch adds a special 'polled interrupt' handler for timer based
software interrupts.

handle_simple_irq() will respond to excessive unhandled interrupts
(as are expected for a polling timer interrupt) by disabling the
apparently unhandled interrupt source.

handle_polled_irq() prevents this by setting the IRQS_POLL_INPROGRESS
flag which will cause the unhandled interrupt events to be ignored.

This is a temporary hack to allow timer based polling of the Atari ROM
port network and USB cards only. Suggestions on how to properly handle
this in the normal interrupt framework are most welcome.

Signed-off-by: Michael Schmitz <schmitz@debian.org>
---
 include/linux/irq.h |    1 +
 kernel/irq/chip.c   |   36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index bc4e066..5064385 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -407,6 +407,7 @@ extern void handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_edge_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_edge_eoi_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_simple_irq(unsigned int irq, struct irq_desc *desc);
+extern void handle_polled_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_percpu_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_percpu_devid_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_bad_irq(unsigned int irq, struct irq_desc *desc);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index cbd97ce..667e4c1 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -353,6 +353,42 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(handle_simple_irq);
 
+/**
+ *	handle_polled_irq - Simple and software-decoded IRQs.
+ *	@irq:	the interrupt number
+ *	@desc:	the interrupt description structure for this irq
+ *
+ *	Polled interrupts are sent from a demultiplexing software interrupt
+ *	handler, where no interrupt hardware control is necessary.
+ */
+void
+handle_polled_irq(unsigned int irq, struct irq_desc *desc)
+{
+	raw_spin_lock(&desc->lock);
+
+	if (unlikely(irqd_irq_inprogress(&desc->irq_data)))
+		if (!irq_check_poll(desc))
+			goto out_unlock;
+
+	desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);
+	kstat_incr_irqs_this_cpu(irq, desc);
+
+	if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
+		desc->istate |= IRQS_PENDING;
+		goto out_unlock;
+	}
+
+	desc->istate |= IRQS_POLL_INPROGRESS;
+
+	handle_irq_event(desc);
+
+	desc->istate &= ~(IRQS_POLL_INPROGRESS);
+
+out_unlock:
+	raw_spin_unlock(&desc->lock);
+}
+EXPORT_SYMBOL_GPL(handle_polled_irq);
+
 /*
  * Called unconditionally from handle_level_irq() and only for oneshot
  * interrupts from handle_fasteoi_irq()
-- 
1.7.0.4