linux-kernel - Re: [PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for "acpi" and pass acpi=force to enable ACPI

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Message-Id: <20150119151350.21B65C40948@trevor.secretlab.ca>
Date:	Mon, 19 Jan 2015 15:13:50 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Catalin Marinas <catalin.marinas@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	Mark Rutland <Mark.Rutland@....com>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Will Deacon <Will.Deacon@....com>,
	"wangyijing@...wei.com" <wangyijing@...wei.com>,
	Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Al Stone <al.stone@...aro.org>,
	Timur Tabi <timur@...eaurora.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"phoenix.liyi@...wei.com" <phoenix.liyi@...wei.com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	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>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for
 "acpi" and pass acpi=force to enable ACPI

On Mon, 19 Jan 2015 13:51:45 +0000
, Catalin Marinas <catalin.marinas@....com>
 wrote:
> On Mon, Jan 19, 2015 at 11:55:32AM +0000, Ard Biesheuvel wrote:
> > On 19 January 2015 at 11:42, Catalin Marinas <catalin.marinas@....com> wrote:
> > > On Wed, Jan 14, 2015 at 03:04:52PM +0000, Hanjun Guo wrote:
> > >> From: Al Stone <al.stone@...aro.org>
> > >>
> > >> Introduce one early parameters "off" and "force" for "acpi", acpi=off
> > >> will be the default behavior for ARM64, so introduce acpi=force to
> > >> enable ACPI on ARM64.
> > >>
> > >> Disable ACPI before early parameters parsed, and enable it to pass
> > >> "acpi=force" if people want use ACPI on ARM64. This ensures DT be
> > >> the prefer one if ACPI table and DT both are provided at this moment.
> > > [...]
> > >> --- a/arch/arm64/kernel/setup.c
> > >> +++ b/arch/arm64/kernel/setup.c
> > >> @@ -62,6 +62,7 @@
> > >>  #include <asm/memblock.h>
> > >>  #include <asm/psci.h>
> > >>  #include <asm/efi.h>
> > >> +#include <asm/acpi.h>
> > >>
> > >>  unsigned int processor_id;
> > >>  EXPORT_SYMBOL(processor_id);
> > >> @@ -388,6 +389,8 @@ void __init setup_arch(char **cmdline_p)
> > >>       early_fixmap_init();
> > >>       early_ioremap_init();
> > >>
> > >> +     disable_acpi();
> > >> +
> > >>       parse_early_param();
> > >>
> > >>       /*
> > >
> > > Did we get to any conclusion here? DT being the preferred one is fine
> > > when both DT and ACPI are present but do we still want the kernel to
> > > ignore ACPI altogether if DT is not present? It's a bit harder to detect
> > > the presence of DT at this point since the EFI_STUB added one already. I
> > > guess we could move the "acpi=force" argument passing to EFI_STUB if no
> > > DT is present at boot.
> > 
> > Since the EFI stub populates the /chosen node in DT, I would prefer
> > for it to add a property there to indicate whether it created the DT
> > from scratch rather than adding ACPI specific stuff in there (even if
> > it is just a string to concatenate)
> 
> This works for me. So we could pass "acpi=force" in EFI stub if it
> created the DT from scratch *and* ACPI tables are present (can it detect
> the latter? And maybe it could print something if none are available).
> If that works, the actual kernel can assume that ACPI needs to be
> explicitly enabled via acpi=force, irrespective of how much information
> it has in DT.

Ditto for me. I think this is a fine solution. And, yes, the stub can
easily detect the presence of ACPI by looking in the UEFI config table.

g.

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