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

On Tuesday, June 07, 2011, Frank Hofmann wrote:

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.

In fact, CONFIG_PM_SLEEP = CONFIG_SUSPEND || CONFIG_HIBERNATE_CALLBACKS, so it
should be sufficient to set HIBERNATION.  ARCH_HIBERNATION_POSSIBLE only
causes HIBERNATION to become a valid option (that may or may not be set).

   (my head swirls from writing this ...)

What problem exactly did you have with those settings?

Rafael