From mboxrd@z Thu Jan  1 00:00:00 1970
From: khilman@kernel.org (Kevin Hilman)
Date: Wed, 12 Aug 2015 13:28:06 -0700
Subject: [PATCH 9/9] ARM: smp: Add runtime PM support for CPU hotplug
In-Reply-To: <1438731339-58317-10-git-send-email-lina.iyer@linaro.org> (Lina
 Iyer's message of "Tue, 4 Aug 2015 17:35:39 -0600")
References: <1438731339-58317-1-git-send-email-lina.iyer@linaro.org>
 <1438731339-58317-10-git-send-email-lina.iyer@linaro.org>
Message-ID: <7hoaicmeuh.fsf@deeprootsystems.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Lina Iyer <lina.iyer@linaro.org> 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 <catalin.marinas@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Signed-off-by: Lina Iyer <lina.iyer@linaro.org>

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