linux-kernel - Re: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64

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Date:	Tue, 06 Jan 2015 14:59:27 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linaro-acpi@...ts.linaro.org
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Lv Zheng <lv.zheng@...el.com>, Rob Herring <robh@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Robert Moore <robert.moore@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"jcm@...hat.com" <jcm@...hat.com>, Mark Brown <broonie@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olof@...om.net>
Subject: Re: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64

On Tuesday 06 January 2015 11:20:01 Catalin Marinas wrote:
> On Mon, Jan 05, 2015 at 08:16:30PM +0000, Arnd Bergmann wrote:
> > On Monday 05 January 2015 13:13:02 Catalin Marinas wrote:
> > > > since passing no DT tables to OS but
> > > > acpi=force is missing is a corner case, we can do a follow up patch to
> > > > fix that, does it make sense?
> > > 
> > > Not entirely. Why would no dtb and no acpi=force be a corner case? I
> > > thought this should be the default when only ACPI tables are passed, no
> > > need for an additional acpi=force argument.
> > 
> > We don't really support the case of only ACPI tables for now. The expectation
> > is that you always have working DT support, at least for the next few years
> > as ACPI features are ramping up, and without acpi=force it should not try
> > to use ACPI at all.
> 
> So if both DT and ACPI are present, just use DT unless acpi=force is
> passed. So far I think we agree but what I want to avoid is always
> mandating acpi=force even when the DT tables are missing (in the long
> run).
> 
> Now, what's preventing a vendor firmware from providing only ACPI
> tables? Do we enforce it in some way (arm-acpi.txt, kernel warning etc.)
> that both DT and ACPI are supported, or at least that dts files are
> merged in the kernel first?

We have no way of enforcing what a board vendor ships, so if they want
to have ACPI-only machines for MS Windows, they just won't work by
default on Linux. Once ACPI support is mature enough, we can also
have a whitelist or a different default for using it automatically
when no DT is present.

For drivers merged upstream, I would insist that every driver merged
for an ARM64 platform has a documented DT binding that is used in the
driver.

	Arnd
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