linux-kernel - Re: [PATCH v4 06/13] ARM64 / ACPI: Introduce early

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Message-ID: <20140627105705.GA5677@xora-haswell.xora.org.uk>
Date:	Fri, 27 Jun 2014 11:57:05 +0100
From:	Graeme Gregory <gg@...mlogic.co.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Hanjun Guo <hanjun.guo@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-acpi@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
	lorenzo.pieralisi@....com, rric@...nel.org,
	Al Stone <al.stone@...aro.org>, linaro-acpi@...ts.linaro.org,
	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	Charles.Garcia-Tobin@....com
Subject: Re: [PATCH v4 06/13] ARM64 / ACPI: Introduce early_param for "acpi"

On Fri, Jun 27, 2014 at 11:07:48AM +0200, Arnd Bergmann wrote:
> On Friday 27 June 2014 11:49:29 Hanjun Guo wrote:
> > +
> > +static int __init parse_acpi(char *arg)
> > +{
> > +       if (!arg)
> > +               return -EINVAL;
> > +
> > +       /* "acpi=off" disables both ACPI table parsing and interpreter */
> > +       if (strcmp(arg, "off") == 0) {
> > +               disable_acpi();
> > +       }
> > +       /* acpi=strict disables out-of-spec workarounds */
> > +       else if (strcmp(arg, "strict") == 0) {
> > +               acpi_strict = 1;
> > +       } else {
> > +               /* Core will printk when we return error */
> > +               return -EINVAL;
> > +       }
> > +
> > +       return 0;
> > +}
> > +early_param("acpi", parse_acpi);
> 
> Can you explain in the changelog what happens for the acpi=off case? Does this
> mean we fall back to using data from the dtb instead, or will it just not work?
> 
> If I understand correctly, this option makes sense on PC systems that will
> still be able to boot using the legacy BIOS services and implicit assumptions
> about the hardware, but that never works on arm64.
> 
Yes the way ACPI has been integrated on ARM64 in these patches if you
supply acpi=off it will fall back to DTB if supplied by firmware.

Graeme

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