linux-kernel - Re: [PATCH] ARM: suspend: use flush range instead of flush all

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Date:	Wed, 12 Sep 2012 14:40:45 +0530
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	wzch <wzch@...vell.com>, Dave Martin <dave.martin@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH] ARM: suspend: use flush range instead of flush all

On Wed, Sep 12, 2012 at 2:24 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Wed, Sep 12, 2012 at 01:13:33PM +0530, Shilimkar, Santosh wrote:
>> On Wed, Sep 12, 2012 at 12:48 PM, wzch <wzch@...vell.com> wrote:
>> >  void __cpu_suspend_save(u32 *ptr, u32 ptrsz, u32 sp, u32 *save_ptr)
>> >  {
>> > +       u32 *ptr_orig = ptr;
>> >         *save_ptr = virt_to_phys(ptr);
>> >
>> >         /* This must correspond to the LDM in cpu_resume() assembly */
>> > @@ -26,7 +27,8 @@ void __cpu_suspend_save(u32 *ptr, u32 ptrsz, u32 sp, u32 *save_ptr)
>> >
>> >         cpu_do_suspend(ptr);
>> >
>> > -       flush_cache_all();
>> Lorenzo's patch was limiting above flush to local cache (LOUs) instead
>> of dropping it completely.
>
> Err, that is wrong.  Normally, when CPUs go into suspend, the L1 cache is
> lost entirely.  This is the only flush which many CPUs see of the L1
> cache.
>
> So removing this flush _will_ break suspend to RAM on existing CPUs.

As mentioned, keeping that flush till inner shareability domain(L1) should be
enough. In fact if that part gets pushed down to the finisher() which any
way needs to take care of the cache maintenance, we can get rid of completely.

At least limiting the flush to local cache instead of all cache levels should
be fixed.

Regards
Santosh
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