[PATCH] ARM: formalize an IPI for CPU wake-ups

[ccross@google.com (Colin Cross)]

On Wed, Aug 1, 2012 at 2:42 AM, Kukjin Kim <kgene.kim@samsung.com> wrote:
> Stephen Boyd wrote:
>>
>> On 07/10/12 23:34, Kukjin Kim wrote:
>> > Stephen Boyd wrote:
>> >> Great. Kukjin Kim, can exynos use SGI0? It looks like exynos is the
>> only
>> >> one left to move to SGI0.
>> >>
>> > Yeah, EXYNOS can use SGI0 instead of SGI1 :)
>> >
>> >
>>
>> Russell, can we apply something like this?
>>
> Please feel free to add my ack on following change.
>
> Acked-by: Kukjin Kim <kgene.kim@samsung.com>
>

When testing coupled cpuidle on Exynos5, I found that sending an IPI
does not successfully wake up CPU1.  CPU1 is in a wfe with interrupts
masked, not a wfi, so an interrupt is not able to wake it up.  It
tends to wake up anyways because the next time a spin lock is
unlocked, often during a timer interrupt on CPU0, CPU0 executes an sev
which wakes up CPU1.  You can see that the IPI is unnecessary by
removing the gic_raise_softirq and replacing it with dsb_sev().