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-rw-r--r--Documentation/power/suspend-and-interrupts.txt16
1 files changed, 13 insertions, 3 deletions
diff --git a/Documentation/power/suspend-and-interrupts.txt b/Documentation/power/suspend-and-interrupts.txt
index 50493c9284b4..8afb29a8604a 100644
--- a/Documentation/power/suspend-and-interrupts.txt
+++ b/Documentation/power/suspend-and-interrupts.txt
@@ -112,8 +112,9 @@ any special interrupt handling logic for it to work.
IRQF_NO_SUSPEND and enable_irq_wake()
-------------------------------------
-There are no valid reasons to use both enable_irq_wake() and the IRQF_NO_SUSPEND
-flag on the same IRQ.
+There are very few valid reasons to use both enable_irq_wake() and the
+IRQF_NO_SUSPEND flag on the same IRQ, and it is never valid to use both for the
+same device.
First of all, if the IRQ is not shared, the rules for handling IRQF_NO_SUSPEND
interrupts (interrupt handlers are invoked after suspend_device_irqs()) are
@@ -122,4 +123,13 @@ handlers are not invoked after suspend_device_irqs()).
Second, both enable_irq_wake() and IRQF_NO_SUSPEND apply to entire IRQs and not
to individual interrupt handlers, so sharing an IRQ between a system wakeup
-interrupt source and an IRQF_NO_SUSPEND interrupt source does not make sense.
+interrupt source and an IRQF_NO_SUSPEND interrupt source does not generally
+make sense.
+
+In rare cases an IRQ can be shared between a wakeup device driver and an
+IRQF_NO_SUSPEND user. In order for this to be safe, the wakeup device driver
+must be able to discern spurious IRQs from genuine wakeup events (signalling
+the latter to the core with pm_system_wakeup()), must use enable_irq_wake() to
+ensure that the IRQ will function as a wakeup source, and must request the IRQ
+with IRQF_COND_SUSPEND to tell the core that it meets these requirements. If
+these requirements are not met, it is not valid to use IRQF_COND_SUSPEND.