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    SubjectRe: [PATCH] kbuild: document recursive dependency limitation / resolution
    On 07/29/15 13:09, Luis R. Rodriguez wrote:
    > From: "Luis R. Rodriguez" <mcgrof@suse.com>
    >
    > Recursive dependency issues with kconfig are unavoidable due to
    > some limitations with kconfig, since these issues are recurring
    > provide a hint to the user how they can resolve these dependency
    > issues and also document why such limitation exists.
    >
    > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    > Cc: James Bottomley <jbottomley@odin.com>
    > Cc: Josh Triplett <josh@joshtriplett.org>
    > Cc: Paul Bolle <pebolle@tiscali.nl>
    > Cc: Herbert Xu <herbert@gondor.apana.org.au>
    > Cc: Takashi Iwai <tiwai@suse.de>
    > Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
    > Cc: Michal Marek <mmarek@suse.com>
    > Cc: Jonathan Corbet <corbet@lwn.net>
    > Cc: linux-kbuild@vger.kernel.org
    > Cc: linux-doc@vger.kernel.org
    > Cc: linux-kernel@vger.kernel.org
    > Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
    > ---
    >
    > I've cc'd Roberto and Stefano as I think we might be able to in the
    > long term use some of their work on package dependency and solvers for
    > this problem [0] [1] [2]. This last part -- just consider it long term
    > focused.
    >
    > [0] https://upsilon.cc/~zack/research/publications/splc2010-fd-deps.pdf
    > [1] https://ocaml.org/meetings/ocaml/2014/preferences-2014-09-05-slides.pdf
    > [2] https://www.youtube.com/watch?v=GSOcRQvZg8w
    >
    > Documentation/kbuild/kconfig-language.txt | 22 ++++++++++++++++++++++
    > scripts/kconfig/symbol.c | 2 ++
    > 2 files changed, 24 insertions(+)
    >
    > diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
    > index 350f733bf2c7..7e0510d1cef7 100644
    > --- a/Documentation/kbuild/kconfig-language.txt
    > +++ b/Documentation/kbuild/kconfig-language.txt
    > @@ -393,3 +393,25 @@ config FOO
    > depends on BAR && m
    >
    > limits FOO to module (=m) or disabled (=n).
    > +
    > +Kconfig recursive dependency limitations
    > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    > +
    > +If you've hit the Kconfig error: "recursive dependency detected" you've run
    > +into a recursive dependency issue with Kconfig. Kconfig does not do recursive
    > +dependency resolution, this has a few implications for Kconfig file writers. In

    maybe s/,/;/

    > +practice it means that for instance if a driver A selects a few kconfig symbols
    > +another driver B which selects any of these symbols cannot negate any of the
    > +symbols the driver A selected. Because of this current limitation developers
    > +who run into this type of recursive dependency issue have two diverging
    > +options:
    > +
    > + a) Either swap all "select FOO" to "depends on FOO" or,
    > + b) Change the offending "depends on FOO" to "select FOO"
    > +
    > +Kconfig's limitations can be addressed by implementing a SAT solver for it,
    > +but until then, Kconfig is limitted to require developers to use one of

    limited

    > +the above two mechanisms to address recursive dependency issues. For more
    > +details you can refer to this thread and discussion:
    > +
    > +http://lkml.kernel.org/r/1432241149-8762-1-git-send-email-mcgrof@do-not-panic.com


    --
    ~Randy


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