linux-kernel - Re: [PATCH v4 05/18] ARM64 / ACPI: Introduce sleep-arm.c

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Date:	Fri, 12 Sep 2014 17:10:32 -0400
From:	Jon Masters <jcm@...hat.com>
To:	Graeme Gregory <gg@...mlogic.co.uk>
CC:	Hanjun Guo <hanjun.guo@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <mark.rutland@....com>,
	Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>, linaro-acpi@...ts.linaro.org,
	Marc Zyngier <marc.zyngier@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Robert Moore <robert.moore@...el.com>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	Mark Brown <broonie@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, Charles.Garcia-Tobin@....com
Subject: Re: [PATCH v4 05/18] ARM64 / ACPI: Introduce sleep-arm.c

On 09/12/2014 04:03 PM, Graeme Gregory wrote:
> On Fri, Sep 12, 2014 at 03:43:36PM -0400, Jon Masters wrote:
>> On 09/12/2014 10:00 AM, Hanjun Guo wrote:
>>> From: Graeme Gregory <graeme.gregory@...aro.org>
>>>
>>> ACPI 5.1 does not currently support S states for ARM64 hardware but
>>> ACPI code will call acpi_target_system_state() for device power
>>> managment, so introduce sleep-arm.c to allow other drivers to function
>>> until S states are defined.
>>
>> Aside: ACPI5.1 does define the Platform Communication Channel and CPC
>> (Collaborative Processor Performance Control). Some details need to be
>> fleshed out there for practical 64-bit ARMv8 server systems, but the
>> underpinnings and mechanisms are in place in the 5.1 specification that
>> can be built upon over time to achieve practical S-State equivalence.
                                                    ^ meant C/P sorry

> Disagree, S-States are about going to sleep or hibernating, that is
> nothing to do with CPU Performance.

Correct. In replying to the above, I was thinking about power and
performance management of components  - CPU (C/P), and device (D)
specific power/performance states - not the overall system (S) state,
and I went off on a tangent. That was off-topic. For the actual topic at
hand, that of global sleep, you are correct that only G0 (S0) and S5 are
really defined today. Though I do think that the PCC might be used to
actually implement overall system sleep state transitions later.

Jon.

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