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    Subjectkconfig `bool' (was: Re: [PATCH 13/13] fix ps3fb glue allowing a modular build)
    On Wed, 14 Mar 2007, Linus Torvalds wrote:
    > On Wed, 14 Mar 2007, Al Viro wrote:
    > > Nope. How can kconfig distinguish that from a boolean option in modular
    > > driver? bool *can* depend on tristate and be selected when tristate is
    > > set to m.
    > Btw, this is one of those things that easily causes problems.
    > In many ways it would be nice if we had two different kinds of "bool": one
    > where "m" in the dependency chain means "y" is ok, and one where "m" means
    > "n".
    > We used to have "dep_bool" and "dep_mbool" for this, a long time ago. It
    > got dropped in the Kconfig language rewrite, and I think it was a mistake.
    > So I think it would be nice to re-introduce it. As it is, we have a number
    > of Kconfig language constructs that are just unnecessarily hard to
    > understand, because we end up having to add a "= y" or similar.
    > The rule *used* to be: "dep_mbool" was a boolean that was valid even for
    > modules, while "dep_bool" was a boolean that was valid only for straigth
    > "y", and a module would turn it off.
    > Maybe not "bool" vs "mbool", but it might be nice to have
    > bool FB_PS3
    > depends strictly on FB
    > ie a "depends strictly" refuses to upgrade a bool dependency from "m" to
    > "y", while a regular depends allows it.
    > Or something.. The "depends strictly on X" thing would really be just a
    > mental shorthand for "depends on (X)=y" (it's actually longer to type, but
    > I think it's a bit more intuitive, thus "mental shortcut").

    I've been thinking about this a bit more...

    Kconfig knows about the following types:
    o bool
    o tristate
    o string
    o hex
    o int

    However, from a semantical point of view, they can be subdivided in 2 classes:
    1. driver/subsystem/library enablers (i.e. things that are used in a Makefile
    to decide whether to compile a unit or not):
    o tristate (y=builtin, m=loadable, n=disabled)
    o bool (y=builtin, n=disabled)
    2. options (i.e. things that control some features, limits, or default
    o bool (y=true, n=false)
    o string (literal)
    o hex (literal)
    o int (literal)

    The confusion arises from the 2 different semantics for `bool': for the former,
    a `depends on' obviously cannot be `builtin' if the dependency is `modular',
    while for the latter, it can be `true' if the dependency is `modular'.

    It would be nice if Kconfig would make the distinction between the two types of
    `bool' explicit. Anyone with a good replacement name for the first type of
    `bool'? I can't find one.



    Geert Uytterhoeven -- Sony Network and Software Technology Center Europe (NSCE) ------- The Corporate Village, Da Vincilaan 7-D1
    Voice +32-2-7008453 Fax +32-2-7008622 ---------------- B-1935 Zaventem, Belgium
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