From: Arnd Bergmann <arnd@arndb.de>
To: Lukas Wunner <lukas@wunner.de>
Cc: Andreas Noever <andreas.noever@gmail.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] thunderbolt: fix compile-test dependencies
Date: Thu, 17 Nov 2016 16:29:05 +0100
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On Thursday, November 17, 2016 4:12:07 PM CET Lukas Wunner wrote:
> On Thu, Nov 17, 2016 at 03:10:11PM +0100, Arnd Bergmann wrote:
> > On Thursday, November 17, 2016 2:53:55 PM CET Lukas Wunner wrote:
> > > Hm, so far Thunderbolt is (unfortunately) an Intel proprietary
> > > technology that is only available on x86, so compiling anything
> > > in drivers/thunderbolt/ on other arches doesn't seem to make much
> > > sense.  So maybe a "depends on X86" would be more appropriate?
> > 
> > I also found that we need "depends on ACPI" because APPLE_PROPERTIES
> > does "select EFI_DEV_PATH_PARSER" and that requires APCI...
> 
> There's a series coming up to power the Thunderbolt controller
> down when nothing is plugged in and this is done via ACPI.
> This commit (slated for 4.11) was going to add a dependency on
> ACPI anyway:
> https://github.com/l1k/linux/commit/c1f379d5dee4
> 
> So adding "depends on ACPI" now would be fine I guess.

It would take care of ARM, but not ARM64: ARM64 has ACPI
and EFI_STUB, but cannot build APPLE_PROPERTIES. Adding
the ACPI dependency by itself would not be sufficient.

> > > One could argue that compiling on other arches helps avoid x86-isms
> > > in case Thunderbolt does become available on other arches one day,
> > > then again it seems like an enormous waste of CPU cycles. *shrug*
> > > 
> > > Opinions?
> > 
> > We try to avoid adding architecture-specific dependencies that
> > prevent build testing, and we are adding '|| COMPILE_TEST' to
> > a lot of drivers for this. We could use 'depends on X86 ||
> > COMPILE_TEST' here, but that wouldn't help the problem on ARM.
> 
> Yes, "depends on X86 || COMPILE_TEST" sounds like the right thing
> to do, independently of the build breakage at hand.

Ok.

> > Another option would be to use 'depends on APPLE_PROPERTIES ||
> > APPLE_PROPERTIES=n', which would force the thunderbolt driver
> > to be a loadable module if APPLE_PROPERTIES is one, but otherwise
> > just allow all configurations.
> 
> APPLE_PROPERTIES is bool, not tristate, so this would work.
> However the solution you proposed earlier ("select APPLE_PROPERTIES if
> (X86 && EFI_STUB)") is more explicit and easier to understand,
> thus seems preferable to me.

Ok, sounds good. That should also fix ARM64 then.

	Arnd