From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx> 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@xxxxxxxxxxxxxx> Cc: James Bottomley <jbottomley@xxxxxxxx> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> Cc: Paul Bolle <pebolle@xxxxxxxxxx> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Cc: Takashi Iwai <tiwai@xxxxxxx> Cc: "Yann E. MORIN" <yann.morin.1998@xxxxxxx> Cc: Michal Marek <mmarek@xxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: linux-kbuild@xxxxxxxxxxxxxxx Cc: linux-doc@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx> --- 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 +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 +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@xxxxxxxxxxxxxxxx diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c index 70c5ee189dce..4d61b7490dad 100644 --- a/scripts/kconfig/symbol.c +++ b/scripts/kconfig/symbol.c @@ -1117,6 +1117,8 @@ static void sym_check_print_recursive(struct symbol *last_sym) if (stack->sym == last_sym) fprintf(stderr, "%s:%d:error: recursive dependency detected!\n", prop->file->name, prop->lineno); + fprintf(stderr, "For a resolution refer to Documentation/kbuild/kconfig-language.txt\n"); + fprintf(stderr, "section \"Kconfig recursive dependency limitations\"\n"); if (stack->expr) { fprintf(stderr, "%s:%d:\tsymbol %s %s value contains %s\n", prop->file->name, prop->lineno, -- 2.3.2.209.gd67f9d5.dirty -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
