irqchip: Add include guard to irq-partition-percpu.h

Add a header include guard just in case.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 234

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation this program is
distributed in the hope that it will be useful but without any
warranty without even the implied warranty of merchantability or
fitness for a particular purpose see the gnu general public license
for more details you should have received a copy of the gnu general
public license along with this program if not see http www gnu org
licenses

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 503 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Enrico Weigelt <info@metux.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190602204653.811534538@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

irqchip: Add per-cpu interrupt partitioning library

We've unfortunately started seeing a situation where percpu interrupts
are partitioned in the system: one arbitrary set of CPUs has an
interrupt connected to a type of device, while another disjoint
set of CPUs has the same interrupt connected to another type of device.

This makes it impossible to have a device driver requesting this interrupt
using the current percpu-interrupt abstraction, as the same interrupt number
is now potentially claimed by at least two drivers, and we forbid interrupt
sharing on per-cpu interrupt.

A solution to this is to turn things upside down. Let's assume that our
system describes all the possible partitions for a given interrupt, and
give each of them a unique identifier. It is then possible to create
a namespace where the affinity identifier itself is a form of interrupt
number. At this point, it becomes easy to implement a set of partitions
as a cascaded irqchip, each affinity identifier being the HW irq.

This allows us to keep a number of nice properties:
- Each partition results in a separate percpu-interrupt (with a restrictied
affinity), which keeps drivers happy.
- Because the underlying interrupt is still per-cpu, the overhead of
the indirection can be kept pretty minimal.
- The core code can ignore most of that crap.

For that purpose, we implement a small library that deals with some of
the boilerplate code, relying on platform-specific drivers to provide
a description of the affinity sets and a set of callbacks.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Link: http://lkml.kernel.org/r/1460365075-7316-4-git-send-email-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>