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SubjectRe: [PATCH 1/4] kconfig: introduce the "imply" keyword
On Thu, Oct 20, 2016 at 03:52:04PM +0100, Edward Cree wrote:
> On 20/10/16 00:42, Nicolas Pitre wrote:
> > diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
> > index 069fcb3eef..c96127f648 100644
> > --- a/Documentation/kbuild/kconfig-language.txt
> > +++ b/Documentation/kbuild/kconfig-language.txt
> > @@ -113,6 +113,33 @@ applicable everywhere (see syntax).
> > That will limit the usefulness but on the other hand avoid
> > the illegal configurations all over.
> >
> > +- weak reverse dependencies: "imply" <symbol> ["if" <expr>]
> > + This is similar to "select" as it enforces a lower limit on another
> > + symbol except that the "implied" config symbol's value may still be
> > + set to n from a direct dependency or with a visible prompt.
> > + Given the following example:
> > +
> > + config FOO
> > + tristate
> > + imply BAZ
> > +
> > + config BAZ
> > + tristate
> > + depends on BAr
> > +
> > + The following values are possible:
> > +
> > + FOO BAR BAR's default choice for BAZ
> Should the third column not be "BAZ's default"?
> > + --------------- --------------- --------------- --------------
> > + n y n N/m/y
> > + m y m M/y/n
> > + y y y Y/n
> > + y n * N
> Also, I don't think having any FOO=y should preclude BAZ=m. Suppose both
> FOO and FOO2 imply BAZ, FOO=y and FOO2=m. Then if BAZ-features are only
> desired for driver FOO2, BAz=m makes sense.

That's exactly the problem that motivated "imply" in the first place:
while that's *possible*, it means the user needs to know that they're
breaking BAZ support for driver FOO.

In theory, someone could extend the UI to note the symbols with an
"imply" for a given symbol and provide additional help for the implied
symbol that explains the implications. In that case, it might make
sense to allow the user to explicitly mark a symbol as 'm', with
appropriate explanations of the implications. But in the absence of
that, the simple solution seems like preventing 'm' for a symbol implied
by a symbol marked as 'y'.

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