Message-ID: <20150119180122.GJ21553@leverpostej>
Date:	Mon, 19 Jan 2015 18:01:22 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	"jcm@...hat.com" <jcm@...hat.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"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 05:52:33PM +0000, Catalin Marinas wrote:
> 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.

Not strictly true once kexec is in place. Then it becomes a stub ->
kernel -> kernel -> kernel -> ... interface, alnog with the rest of the
properties the stub puts in the DTB.

Having something like /chosen/linux,uefi-stub-generated-dtb sounds sane
regardless.

Mark.
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