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

[Rafael J. Wysocki]

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