Subject: [PATCH 9/9] ARM: smp: Add runtime PM support for CPU hotplug

From: [email-masked] (Kevin Hilman)
Date: Wed, 12 Aug 2015 13:28:06 -0700

Lina Iyer <[email-masked]> writes:

> Enable runtime PM for CPU devices. Do a runtime get of the CPU device
> when the CPU is hotplugged in and a runtime put of the CPU device when
> the CPU is hotplugged off. When all the CPUs in a domain are hotplugged
> off, the domain may also be powered off and cluster_pm_enter/exit()
> notifications are be sent out.
>
> Cc: Catalin Marinas <[email-masked]>
> Cc: Mark Rutland <[email-masked]>
> Cc: Lorenzo Pieralisi <[email-masked]>
> Signed-off-by: Lina Iyer <[email-masked]>

How does the runtiem PM usage with hotplug work with the runtime PM
usage in idle?

IIUC, when a CPU is hotplugged in, it will always have a usecount of at
least 1, right?  and if it's not idle, it will have done a _get() so it
will have a usecount of at least 2.   So I'm not quite seeing how the
usecount will ever go to zero in idle and allow the domain to power_off.

Kevin