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

[Shilimkar, Santosh]

On Tue, Aug 7, 2012 at 10:30 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Mon, Aug 06, 2012 at 01:41:06PM -0700, Colin Cross wrote:
>> 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().
>
> That's good news; that supports my assertion that the SMP bringup code
> we see on various platforms as copies from the Realview code was done
> without much thought about what is actually required.
>
> It's good that you're looking into this, and fixing the code on the CPUs
> you have access to.  I rather wish we'd made it a requirement for people
> to _document_ the actual bringup conditions in the kernel for their
> hardware before we accepted their SMP support code.
>
Movement to SGI0 for all ARM platform was also discussed when I
was trying to fix the "Unknown IPI message 0x1" warning with patch [1]

For OMAP too, the SGI0 works.

Regards
Santosh

[1 ] http://lists.infradead.org/pipermail/linux-arm-kernel/2011-January/038430.html