[RFC PATCH 0/6] ARM: augment cache flushing API

[Lorenzo Pieralisi]

This patch series provides an update of a previous posting:

http://www.spinics.net/lists/arm-kernel/msg169075.html

Main changes:
 - Changed the new API to Level of Unification Inner Shareable (LoUIS)
 - Fixed a pointer bug in __cpu_suspend_save code update
 - Added patches to update __cpu_disable and __v7_setup to LoUIS API
 - Changed the v7 dcache level function to make it clean/invalidate a specific
   level instead of up to a certain level

v7 ARM architecture introduced the concept of cache levels and relative
control registers to manage them. Cache operations that operate on set/way
require to define the cache level at which maintenance operations are carried
out by using coprocessor registers.

Processors like A7/A15 integrates a unified L2 that is part of the cache
level hierarchy; this implies that cache operations operating on all levels
also end up cleaning the L2 unified cache which is a very time consuming
operation and it is not needed for some power-down operations like single CPU
shutdown.

For v7, flush_kern_all() cleans all the cache levels up to the Level of
Coherency which includes L2 in it. This is suboptimal for code paths that end
up shutting-down a single processor like CPU hotplug and CPU idle, where only
per-CPU cache state (ie L1 integrated cache) has to be cleaned and invalidated.

To fix this performance issue this patchset introduces cache LoUIS (Level of
Unification Inner Shareable) maintenance operations in the kernel.

A new cache operations pointer is added to cpu_cache_fns

void (*flush_kern_cache_louis)(void);

that allows to clean and invalidate all data cache levels up to the LoUIS and
invalidate the instruction cache. This new API should provide a sufficiently
optimized API to be used in generic C code in the kernel for power management
operations on most v7 systems.

For architecture versions previous to v7, flush_kern_cache_louis() falls back
to flush_kern_all() leaving the current behaviour unchanged.

In order to allow finer grain operations on cache levels, this series also
defines an assembly stub for v7 that allows to clean and invalidate a specific
data cache level and it is provided for completeness.

For A9/A5 processors Level of Unification Inner Shareable and Level of
Coherency are equivalent hence this patch should not affect current kernel
behaviour in any way when run on A9/A5 based systems, but should nonetheless
be thoroughly tested on them.

Tested on:
  - OMAP4 (S2R, cpuidle and hotplug)
  - OMAP5 (out of tree code) (S2R, cpuidle and hotplug)
  - TC2 big.LITTLE testchip (out of tree code) (cpuidle, on both A7 and A15
    clusters)

Lorenzo Pieralisi (4):
  ARM: mm: define LoUIS API for cache maintenance ops
  ARM: mm: add v7 cache LoUIS API implementation
  ARM: kernel: update cpu_suspend code to use cache LoUIS operations
  ARM: kernel: update __cpu_disable to use cache LoUIS maintenance API

Santosh Shilimkar (2):
  ARM: mm: add v7 dcache level API
  ARM: mm: update __v7_setup() to the new LoUIS cache maintenance API

 arch/arm/include/asm/cacheflush.h | 17 +++++++++++
 arch/arm/kernel/smp.c             |  5 +++-
 arch/arm/kernel/suspend.c         | 17 ++++++++++-
 arch/arm/mm/cache-v7.S            | 62 +++++++++++++++++++++++++++++++++++++--
 arch/arm/mm/proc-macros.S         |  7 ++++-
 arch/arm/mm/proc-v7.S             |  2 +-
 6 files changed, 103 insertions(+), 7 deletions(-)

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1.7.12