[RFC PATCH v4] ARM hibernation/suspend-to-disk support

Hi,

time for another round on this one...

This got quite a bit cleaned up now.

There's now no more need for a "swsusp context" at all. The code uses cpu_suspend/resume and keeps the snapshot state on the stack while writing it out.

There are a few dependencies this patch brings in:

* due to the use of cpu_suspend / cpu_resume, it'll only apply as-is
  to kernels no older than f6b0fa02e8b0708d17d631afce456524eadf87ff,
  where Russell King introduced the generic interface.
  Patching these into older kernels is a little work.

* it temporarily uses swapper_pg_dir and establishes 1:1 mappings there
  for a MMU-off transition, which is necessary before resume.
  In order to tear these down afterwards, identity_mapping_del() needs
  to be called; for some reason that's #ifdef CONFIG_SMP ...

* it needs to "catch" sleep_save_sp after cpu_suspend() so that resume
  can be provided with the proper starting point.
  This requires an ENTRY(sleep_save_sp) in arch/arm/kernel/sleep.S so
  that the symbol becomes public.

* it assumes cpu_reset will disable the MMU. cpu_v6_reset/cpu_v7_reset
  are currently not doing so (amongst some other minor chip types).

* there's kind of a circular dependency between CONFIG_HIBERNATION and
  CONFIG_PM_SLEEP, on ARM. The latter is necessary so that cpu_suspend
  and cpu_resume are compiled in, but it cannot be selected via
  ARCH_HIBERNATION_POSSIBLE because CONFIG_PM_SLEEP depends on
  CONFIG_HIBERNATION_INTERFACE - selected by CONFIG_HIBERNATION.

  Consequence is that right now, both CONFIG_PM_SLEEP and ...HIBERNATION
  must be set in your defconfig file to be able to compile.

  (my head swirls from writing this ...)

Otherwise, this is by far the cleanest in the series yet.


I've tested this on ARM1176; still need to do OMAP3 (Cortex-A8), will report on that.


Please let me know what you think,
FrankH.