genirq: Add untracked irq handler

This adds a software irq handler for controllers that multiplex
interrupts from multiple devices, but don't know which device generated
the interrupt. For these devices, the irq handler that demuxes must
check every action for every software irq using the same h/w irq in order
to find out which device generated the interrupt. This will inevitably
trigger spurious interrupt detection if we are noting the irq.

The new irq handler does not track the handling for spurious interrupt
detection. An irq that uses this also won't get stats tracked since it
didn't generate the interrupt, nor added to randomness since they are
not random.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org
Cc: Jon Derrick <jonathan.derrick@intel.com>
Link: http://lkml.kernel.org/r/1466200821-29159-1-git-send-email-keith.busch@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 43 insertions, 0 deletions

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index ad8131473774..b4c1bc7c9ca2 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -426,6 +426,49 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(handle_simple_irq);
 
+/**
+ *      handle_untracked_irq - Simple and software-decoded IRQs.
+ *      @desc:  the interrupt description structure for this irq
+ *
+ *      Untracked interrupts are sent from a demultiplexing interrupt
+ *      handler when the demultiplexer does not know which device it its
+ *      multiplexed irq domain generated the interrupt. IRQ's handled
+ *      through here are not subjected to stats tracking, randomness, or
+ *      spurious interrupt detection.
+ *
+ *      Note: Like handle_simple_irq, the caller is expected to handle
+ *      the ack, clear, mask and unmask issues if necessary.
+ */
+void handle_untracked_irq(struct irq_desc *desc)
+{
+        unsigned int flags = 0;
+
+        raw_spin_lock(&desc->lock);
+
+        if (!irq_may_run(desc))
+                goto out_unlock;
+
+        desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);
+
+        if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
+                desc->istate |= IRQS_PENDING;
+                goto out_unlock;
+        }
+
+        desc->istate &= ~IRQS_PENDING;
+        irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);
+        raw_spin_unlock(&desc->lock);
+
+        __handle_irq_event_percpu(desc, &flags);
+
+        raw_spin_lock(&desc->lock);
+        irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
+
+out_unlock:
+        raw_spin_unlock(&desc->lock);
+}
+EXPORT_SYMBOL_GPL(handle_untracked_irq);
+
 /*
  * Called unconditionally from handle_level_irq() and only for oneshot
  * interrupts from handle_fasteoi_irq()