linux-kernel - Re: [PATCH] thunderbolt: fix compile-test dependencies

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Date:   Thu, 17 Nov 2016 16:12:07 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thunderbolt: fix compile-test dependencies

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.


> > 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.


> 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.

Thanks!

Lukas