linux-kernel - Re: [PATCH v2 0/5] CPU PM notifiers

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Message-ID: <4E6AFB3E.3020902@ti.com>
Date:	Sat, 10 Sep 2011 11:23:02 +0530
From:	Santosh <santosh.shilimkar@...com>
To:	Kevin Hilman <khilman@...com>
CC:	linux-arm-kernel@...ts.infradead.org, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org, rjw@...k.pl, ccross@...roid.com
Subject: Re: [PATCH v2 0/5] CPU PM notifiers

On Friday 09 September 2011 11:30 PM, Kevin Hilman wrote:
> Santosh Shilimkar<santosh.shilimkar@...com>  writes:
>
> [...]
>
>> This patch set tries to address concerns with platform pm code
>> calling into the driver for every block in the Cortex A9s
>> during idle, hotplug, and suspend.  The first patch adds cpu pm
>> notifiers that can be called by platform code, the second uses
>> the notifier to save and restore the GIC state, and the third
>> saves the VFP state.
>>
>> The notifiers are used for two types of events, CPU PM events and
>> CPU cluster PM events.  CPU PM events are used to save and restore
>> per-cpu context when a single CPU is preparing to enter or has
>> just exited a low power state.  For example, the VFP saves the
>> last thread context, and the GIC saves banked CPU registers.
>>
>> CPU cluster events are used after all the CPUs in a power domain
>> have been prepared for the low power state.  The GIC uses these
>> events to save global register state.
>
> Stepping back from my earlier objections, I think I had a fundamental
> misunderstanding about what these notifiers should be used for.
>
> The current assumptions/goals seem to be
>
> 1) used only for devices in the same power domain as the CPU (cluster)
> 2) use only for one specific power state of the CPU (cluster): off.
>
> For awhile now, we've been discussing how to better coordinate CPU PM
> transitions (CPUidle) with non-CPU PM transitions (runtime PM) for
> devices that are tightly coupled to the CPU, but not necessarily in the
> same powerdomain.
>
> I was assuming (and hoping) that CPU PM notifiers could be used to do
> that, but the more I think about it, I don't think we can achieve the
> current CPU PM goals and the coordination with runtime PM with this
> series.
>
> I think it's more likely that we'll need to do some work with Rafael's
> new PM domains to make that work correctly.
>
> So, I'll retract my objections to this series, and feel free to add
>
> Reviewed-by: Kevin Hilman<khilman@...com>
>
Will add.
Thanks for the review Kevin.

Regards
Santosh

Regards

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