linux-kernel - Re: [PATCH v3 00/17] Introduce ACPI for ARM64 based on ACPI 5.1

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Message-ID: <20140911160627.GU6558@xora-haswell.xora.org.uk>
Date:	Thu, 11 Sep 2014 17:06:27 +0100
From:	Graeme Gregory <gg@...mlogic.co.uk>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Mark Rutland <Mark.Rutland@....com>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Will Deacon <Will.Deacon@....com>,
	Lv Zheng <lv.zheng@...el.com>, Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Robert Moore <robert.moore@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Mark Brown <broonie@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v3 00/17] Introduce ACPI for ARM64 based on ACPI 5.1

On Thu, Sep 11, 2014 at 04:57:24PM +0100, Sudeep Holla wrote:
> 
> 
> On 11/09/14 16:37, Catalin Marinas wrote:
> >On Thu, Sep 11, 2014 at 02:29:34PM +0100, Grant Likely wrote:
> >>Regarding the requests to refactor ACPICA to work better for ARM. I
> >>completely agree that it should be done, but I do not think it should be
> >>a prerequisite to getting this core support merged. That kind of
> >>refactoring is far easier to justify when it has immediate improvement
> >>on the mainline codebase, and it gives us a working baseline to test
> >>against. Doing it the other way around just makes things harder.
> >
> >I have to disagree here. As I said, I'm perfectly fine with refactoring
> >happening later but I'm not happy with compiling in code with undefined
> >behaviour on ARM that may actually be executed at run-time.
> >
> >I'm being told one of the main advantages of ACPI is forward
> >compatibility: running older kernels on newer hardware (potentially with
> >newer ACPI version tables). ACPI 5.1 includes partial support for ARM
> >but the S and C states are not defined yet. We therefore assume that
> >hardware vendors deploying servers using ACPI would not provide such
> >yet to be defined information in ACPI 5.1 tables.
> >
> >What if in a year time we get ACPI 5.2 or 6 (or an errata update)
> >covering the S and C states for ARM? I would expect hardware vendors
> >to take advantage and provide such information in ACPI tables. Can we
> >guarantee that a kernel with the current ACPI patches wouldn't blow up
> >when it tries to interpret the new tables? If we can't guarantee this,
> >we rather fix it now. Some suggestions:
> >
> >a) Make sure code which doesn't have a clear behaviour on ARM is not
> >    compiled in and doesn't even try to interpret such tables on ARM (you
> >    could just go for the latter but I'm not sure how feasible it is)
> 
> This what we have suggested in past especially for this S-state support.
> Currently the core acpi code compiles in sleep support unconditionally.
> That doesn't mean we need to do the same on ARM64, we can easily make
> sure that's not enabled for ARM64 until we have clarification on how to
> support them on ARM in ACPI specification.
> 
> I just pointed out at one "out of spec" workaround done for x86
> "unconditionally" in the code just to tell that it won't work on ARM.
> That shouldn't be misunderstood as demand for refactoring as we have no
> clue how S-state would look on ARM to take up any such task.
> 
For the sleep.c case I worked on this and sent some updates to Hanjun so
it should be compiled out in the next version of the patches.

Graeme

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