linux-kernel - Re: [PATCH v3 02/17] ARM64 / ACPI: Get RSDP and ACPI boot-time tables

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Date:	Tue, 09 Sep 2014 12:41:51 -0400
From:	Jon Masters <jcm@...hat.com>
To:	Catalin Marinas <catalin.marinas@....com>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <Mark.Rutland@....com>,
	Olof Johansson <olof@...om.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Will Deacon <Will.Deacon@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	linux-acpi@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 02/17] ARM64 / ACPI: Get RSDP and ACPI boot-time tables

On 09/09/2014 12:26 PM, Catalin Marinas wrote:
> On Mon, Sep 01, 2014 at 03:57:40PM +0100, Hanjun Guo wrote:
>> diff --git a/arch/arm64/include/asm/acenv.h b/arch/arm64/include/asm/acenv.h
>> new file mode 100644
>> index 0000000..3899ee6
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/acenv.h
>> @@ -0,0 +1,18 @@
>> +/*
>> + * ARM64 specific ACPICA environments and implementation
>> + *
>> + * Copyright (C) 2014, Linaro Ltd.
>> + *   Author: Hanjun Guo <hanjun.guo@...aro.org>
>> + *   Author: Graeme Gregory <graeme.gregory@...aro.org>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#ifndef _ASM_ACENV_H
>> +#define _ASM_ACENV_H
>> +
>> +#define ACPI_FLUSH_CPU_CACHE() WARN_ONCE(1, "Not currently supported on ARM64")
> 
> Does this mean that it will be supported at some point? Looking at the
> places where this function is called, I don't really see how this would
> ever work on ARM. Which means that we add such macro just to be able to
> compile code that would never be used on arm64. I would rather see the
> relevant ACPI files only compiled on x86/IA-64 rather than arm64.

That specific cache behavior is a part of e.g. ACPI C3 state support
(e.g. ACPI5.1 8.1.4 Processor Power State C3). As you note, it's not
going to work on 64-bit ARM as it does on x86, but it's optional to
implement C3 and early 64-bit ARM systems should not report Wbindv flags
in the FADT anyway. They can also set FADT.P_LVL3_LAT > 1000, which has
the effect of disabling C3 support, while also allowing for use of _CST
objects to define more flexible C-States later on.

Jon.

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