linux-kernel - Re: [PATCH RESEND] ACPI/Kconfig: Make ACPI_NFIT depend on EFI

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Date:	Tue, 15 Dec 2015 10:05:22 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] ACPI/Kconfig: Make ACPI_NFIT depend on EFI_STUB on X86

On Tue, Dec 15, 2015 at 9:56 AM, Toshi Kani <toshi.kani@....com> wrote:
> On Tue, 2015-12-15 at 09:53 -0800, Dan Williams wrote:
[..]
>> > > > diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> > > > index 5eef4cb..5368baa 100644
>> > > > --- a/drivers/acpi/Kconfig
>> > > > +++ b/drivers/acpi/Kconfig
>> > > > @@ -441,6 +441,7 @@ config ACPI_NFIT
>> > > >         depends on PHYS_ADDR_T_64BIT
>> > > >         depends on BLK_DEV
>> > > >         depends on ARCH_HAS_MMIO_FLUSH
>> > > > +       depends on !X86 || (X86 && EFI_STUB)
>> > > >         select LIBNVDIMM
>> > > >         help
>> > > >           Infrastructure to probe ACPI 6 compliant platforms for
>> > >
>> > > This seems wrong to me.
>> > >
>> > > In general Kconfig "depends on" are only about compile-time code
>> > > dependency, not about working around random bugs in external
>> > > projects.
>> >
>> > I agree that they do not have a compile dependency, and it looks rather
>> > odd.  On the other hand, proper support of the ACPI NFIT extensions has
>> > a
>> > functional dependency to setup_e820() as this is the only code that can
>> > handle the EFI_PERSISTENT_MEMORY type today.
>>
>> What about non-EFI/legeacy-boot systems that only emit e820-type-7?
>> We lose support for them with this patch, right?
>
> No, having EFI_STUB does not break the legacy BIOS boot.
>

Sorry let me clarify.  A kernel compiled without EFI_STUB loses NFIT
support.  Non-EFI and legacy-boot systems don't have this grub bug to
worry about, so the dependency is overly restrictive, "breaks", those
environments.
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