Re: [PATCH 03/11] ARM: pm: some ARMv7 requires a dsb in resume to ensure correctness

[Catalin Marinas <catalin.marinas@arm.com>]

On 7 September 2011 17:19, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Wed, Sep 07, 2011 at 04:41:32PM +0100, Catalin Marinas wrote:
>> On 1 September 2011 13:49, Russell King - ARM Linux
>> <linux@arm.linux.org.uk> wrote:
>> > Add a dsb after the isb to ensure that the previous writes to the
>> > CP15 registers take effect before we enable the MMU.
>> >
>> > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
>> > ---
>> >  arch/arm/mm/proc-v7.S |    1 +
>> >  1 files changed, 1 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
>> > index dec72ee..a773f4e 100644
>> > --- a/arch/arm/mm/proc-v7.S
>> > +++ b/arch/arm/mm/proc-v7.S
>> > @@ -255,6 +255,7 @@ ENTRY(cpu_v7_do_resume)
>> >        mcr     p15, 0, r4, c10, c2, 0  @ write PRRR
>> >        mcr     p15, 0, r5, c10, c2, 1  @ write NMRR
>> >        isb
>> > +       dsb
>>
>> Isn't an ISB enough here? We usually have the DSB for some background
>> operations like cache maintenance.
>
> That depends whether you're including the effects of the cache
> maintanence instructions in this.  The ARM ARM tells me that
> a DSB is required to ensure that all cache maintanence is issued
> before the dsb is complete at the point that the dsb is executed.

Another minor point, in general we would use the DSB before the ISB
(but that's when the I-cache is enabled).

-- 
Catalin
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