linux-kernel - Re: linux-next: build warning after merge of the arm64 tree

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Date:   Tue, 24 Jul 2018 10:12:18 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: linux-next: build warning after merge of the arm64 tree

On Tue, Jul 24, 2018 at 2:26 AM, AKASHI Takahiro
<takahiro.akashi@...aro.org> wrote:
> On Tue, Jul 24, 2018 at 09:05:45AM +1000, Stephen Rothwell wrote:
>> Hi all,
>>
>> After merging the arm64 tree, today's linux-next build (x86_64
>> allmodconfig) produced this warning:
>
> Where can I find this specific branch?
>
>> drivers/acpi/Kconfig:6:error: recursive dependency detected!
>> drivers/acpi/Kconfig:6:       symbol ACPI depends on EFI
>
> My patch created an additional dependency like:
>   menu ACPI
>     ...
>     depends on IA64 || X86 || (ARM64 && EFI)
>
>> arch/x86/Kconfig:1920:        symbol EFI depends on ACPI
>
> So I don't understand why this change makes a warning on x86_64 build.
> Is this a real recursive dependency?

On x86, we have

config EFI
        bool "EFI runtime service support"
        depends on ACPI

Kconfig cannot know that CONFIG_ARM64 is never set on x86, while
X86 is always set. So to Kconfig it it appears like a recursive
dependency.

The best workaround I can see is to have an intermediate symbol
on ARM64 that is invisible to Kconfig on x86, like

config ARCH_SUPPORTS_ACPI
        def_bool EFI

and then have ACPI depend on that.

       Arnd