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: <20150119175233.GK11835@e104818-lin.cambridge.arm.com>
Date:	Mon, 19 Jan 2015 17:52:33 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Jon Masters <jcm@...hat.com>
Cc:	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	"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>,
	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, Jan 19, 2015 at 04:59:47PM +0000, Jon Masters wrote:
> On 01/19/2015 10:13 AM, Grant Likely wrote:
> > 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.
> 
> I get the point behind doing this, but could we not have it pass in a
> different parameter than =force? Perhaps something new? I'd like to
> separate out the case that it was enabled automatically vs explicitly
> forced on by a user wanting to use ACPI on a system with both tables.

Ard had a point, so we should probably not pass acpi=force from EFI stub
(especially since a user may explicitly pass acpi=off irrespective of DT
presence). Some other property in the chosen node? It's not even an ABI
since that's a contract between EFI stub and the rest of the kernel, so
an in-kernel only interface.

-- 
Catalin
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