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Date:	Sun, 21 Oct 2007 20:14:16 -0700
From:	Randy Dunlap <>
To:	Randy Dunlap <>
Cc:	Sam Ravnborg <>, Henrik Carlqvist <>,,
Subject: Re: tristate and bool not enogh for Kconfig anymore

On Sun, 21 Oct 2007 17:47:48 -0700 Randy Dunlap wrote:

> On Sun, 21 Oct 2007 23:03:13 +0200 Sam Ravnborg wrote:
> > On Sun, Oct 21, 2007 at 09:45:17AM -0700, Randy Dunlap wrote:
> > > > Is there any other way to specify that a functionality can only be built
> > > > as a module, not built into the kernel?
> > > 
> > > config FOO
> > > 	depends on BAR && m
> > > 
> > > restricts FOO to module-only.
> > > 
> > > > In my firsta attempts to post about these tests my post ended up not on
> > > > the mailing list but as a reply to Sam Ravnborg only, apologies for
> > > > that...
> > 
> > This is obviously the right solution.
> > Randy - we should document this somewhere together with more kconfig tips'n'tricks.
> Agreed.

So that's one tip or trick... or common idiom.

> > A new document or do we extend kconfig-language?
> I don't see a need for a separate document.  I would just extend
> kconfig-language.

Another common idiom that we see (and sometimes have problems
with) is this:

When B (module or subsystem) uses interfaces from A (module or
subsystem), A can be linked statically into the kernel image or
can be built as loadable module(s).   This limits how B can be
built.  If A is linked statically into the kernel image, B can be
built statically or as loadable module(s).  However, if A is built
as loadable module(s), then B must be restricted to loadable
module(s) also.  This can be expressed in kconfig language as:

config B
	depends on A = y || A = B

There's also a third issue:  symbols that are specific to a
particular $arch, but they are in Kconfig files that are common
to all arches, so kconfig complains about symbol A refers to
unknown symbol B.  (and I'm just writing this from memory, not
from testing it, so it could be off a bit.)  One example of this
was PS3_PS3AV, as copied from an lkml email of 2007-feb-14:

drivers/video/Kconfig:1604:warning: 'select' used by config symbol 
'FB_PS3' refer to undefined symbol 'PS3_PS3AV'

Someone fixed this one by introducing an intermediate config symbol.
I didn't follow the details of that fix, but we see this problem
enough to warrant explaining how to handle it.  E.g., recently
(from 2007-oct-14) on lkml:

$ make oldconfig >/dev/null
drivers/macintosh/Kconfig:121:warning: 'select' used by config 
symbol 'PMAC_APM_EMU' refers to undefined symbol 'APM_EMULATION'

Adrian, do you know of other items that should be listed here?

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