genirq: Introduce effective affinity mask

There is currently no way to evaluate the effective affinity mask of a
given interrupt. Many irq chips allow only a single target CPU or a subset
of CPUs in the affinity mask.

Updating the mask at the time of setting the affinity to the subset would
be counterproductive because information for cpu hotplug about assigned
interrupt affinities gets lost. On CPU hotplug it's also pointless to force
migrate an interrupt, which is not targeted at the CPU effectively. But
currently the information is not available.

Provide a seperate mask to be updated by the irq_chip->irq_set_affinity()
implementations. Implement the read only proc files so the user can see the
effective mask as well w/o trying to deduce it from /proc/interrupts.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235446.247834245@linutronix.de

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index 8d9498e51585..fcbb1d6d51cb 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -21,6 +21,10 @@ config GENERIC_IRQ_SHOW
 config GENERIC_IRQ_SHOW_LEVEL
        bool
 
+# Supports effective affinity mask
+config GENERIC_IRQ_EFFECTIVE_AFF_MASK
+       bool
+
 # Facility to allocate a hardware interrupt. This is legacy support
 # and should not be used in new code. Use irq domains instead.
 config GENERIC_IRQ_LEGACY_ALLOC_HWIRQ