linux-kernel - Re: [PATCH v3 8/9] ACPI: arm64: use an arch-specific ACPI

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Message-ID: <20150305101705.GB5287@arm.com>
Date:	Thu, 5 Mar 2015 10:17:05 +0000
From:	Will Deacon <will.deacon@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Al Stone <al.stone@...aro.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"robert.moore@...el.com" <robert.moore@...el.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"devel@...ica.org" <devel@...ica.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>
Subject: Re: [PATCH v3 8/9] ACPI: arm64: use an arch-specific ACPI _OSI
 method and ACPI blacklist

On Wed, Mar 04, 2015 at 11:14:50PM +0000, Rafael J. Wysocki wrote:
> On Monday, March 02, 2015 12:00:21 PM Al Stone wrote:
> > On 03/02/2015 10:29 AM, Will Deacon wrote:
> > > On Wed, Feb 25, 2015 at 12:36:24AM +0000, al.stone@...aro.org wrote:
> > >> diff --git a/arch/arm64/kernel/acpi-blacklist.c b/arch/arm64/kernel/acpi-blacklist.c
> > >> new file mode 100644
> > >> index 0000000..1be6a56
> > >> --- /dev/null
> > >> +++ b/arch/arm64/kernel/acpi-blacklist.c
> > >> @@ -0,0 +1,20 @@
> > >> +/*
> > >> + *  ARM64 Specific ACPI Blacklist Support
> > >> + *
> > >> + *  Copyright (C) 2015, Linaro Ltd.
> > >> + *	Author: Al Stone <al.stone@...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.
> > >> + */
> > >> +
> > >> +#define pr_fmt(fmt) "ACPI: " fmt
> > >> +
> > >> +#include <linux/acpi.h>
> > >> +
> > >> +/* The arm64 ACPI blacklist is currently empty.  */
> > >> +int __init acpi_blacklisted(void)
> > >> +{
> > >> +	return 0;
> > >> +}
> > >> diff --git a/arch/arm64/kernel/acpi-osi.c b/arch/arm64/kernel/acpi-osi.c
> > >> new file mode 100644
> > >> index 0000000..bb351f4
> > >> --- /dev/null
> > >> +++ b/arch/arm64/kernel/acpi-osi.c
> > >> @@ -0,0 +1,25 @@
> > >> +/*
> > >> + *  ARM64 Specific ACPI _OSI Support
> > >> + *
> > >> + *  Copyright (C) 2015, Linaro Ltd.
> > >> + *	Author: Al Stone <al.stone@...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.
> > >> + */
> > >> +
> > >> +#define pr_fmt(fmt) "ACPI: " fmt
> > >> +
> > >> +#include <linux/acpi.h>
> > >> +
> > >> +/*
> > >> + * Consensus is to deprecate _OSI for all new ACPI-supported architectures.
> > >> + * So, for arm64, reduce _OSI to a warning message, and tell the firmware
> > >> + * nothing of value.
> > >> + */
> > >> +u32 acpi_osi_handler(acpi_string interface, u32 supported)
> > >> +{
> > >> +	pr_warn("_OSI was called, but is deprecated for this architecture.\n");
> > >> +	return false;
> > >> +}
> > > 
> > > This kinda feels backwards to me. If _OSI is going away, then the default
> > > should be "the architecture doesn't need to do anything", rather than have
> > > new architectures defining a bunch of empty, useless stub code.
> > > 
> > > Anyway we could make this the default in core code and have architectures
> > > that *do* want _OSI override that behaviour, instead of the other way around?
> > > 
> > We could do that; I personally don't have a strong preference either way,
> > so I'm inclined to make it whatever structure Rafael thinks is proper since
> > it affects ACPI code most.  That being said, the current patch structure
> > made sense to me since it wasn't distorting existing code much -- and given
> > the pure number of x86/ia64 machines vs ARM machines using ACPI, that seemed
> > the more cautious approach.
> > 
> > @Rafael: do you have an opinion/preference?
> 
> My preference is to avoid changes in the existing code at least for the time
> being.  Especially if the changes in question are going to affect ia64, unless
> you have an Itanium machine where you can readily test those, that is. :-)

Well, this code doesn't even need to compiled for ia64 if we have those
architectures that want to use _OSI select a Kconfig symbol for it, so I
don't think the testing argument is really that valid. I appreciate that you
want to avoid changing the existing code, but I also don't want to add this
sort of stuff to the architecture code, when it really has nothing to do
with the architecture.

Will
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