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

[Frank Hofmann]

On Thu, 9 Jun 2011, Russell King - ARM Linux wrote:

> On Tue, Jun 07, 2011 at 05:48:17PM +0100, Frank Hofmann wrote:
>> 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.
>
> Another issue is that it uses PHYS_OFFSET in assembly code which is not
> permissible with P2V patching.
>

Would calling something like:

unsigned long __swsusp_arch_get_vpoffset(void *addr)
{
         return (virt_to_phys(addr) - (unsigned long)addr);
}

from the assembly be ok ?

(That's what I've gone for at the moment to address this; a generic func 
somewhere to query for this would obviously be ok as well)

FrankH.