From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v3 02/17] ARM64 / ACPI: Get RSDP and ACPI boot-time tables
Date: Tue, 9 Sep 2014 17:54:45 +0100
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To: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: "hanjun.guo@linaro.org" <hanjun.guo@linaro.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Olof Johansson <olof@lixom.net>, "grant.likely@linaro.org" <grant.likely@linaro.org>, "graeme.gregory@linaro.org" <graeme.gregory@linaro.org>, Arnd Bergmann <arnd@arndb.de>, Sudeep Holla <Sudeep.Holla@arm.com>, Will Deacon <Will.Deacon@arm.com>, Jason Cooper <jason@lakedaemon.net>, Marc Zyngier <Marc.Zyngier@arm.com>, Bjorn Helgaas <bhelgaas@google.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, Mark Brown <broonie@kernel.org>, Rob Herring <robh@kernel.org>, Robert Richter <rric@kernel.org>, Lv Zheng <lv.zheng@intel.com>, Robert Moore <robert.moore@intel.com>, Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>, Liviu Dudau <Liviu.Dudau@arm.com>, Randy Dunlap <rdunlap@infradead.org>, Charles Garcia-Tobin <Charles.Garcia-Tobin@arm.com>, "linux-acpi@vger.kernel.org" <linux-acpi@vge>

On Tue, Sep 09, 2014 at 05:26:49PM +0100, 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@linaro.org>
> > + *   Author: Graeme Gregory <graeme.gregory@linaro.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?

>>From what I recall it's impossible to support as we have no equivalent
of WBINVD -- the possibility migration of dirty cache lines renders it
impossible to guarantee that the caches remain empty (or that data even
left the local caches in the first place).

> 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.

Agreed.

It looks like include/acpi/platform/acenv.h defines an empty
ACPI_FLUSH_CPU_CACHE() stub, so something else should probably be done
to turn the use of ACPI_FLUSH_CPU_CACHE() into a build-time bug on
arm64.

Mark.