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Date:   Mon, 2 Mar 2020 10:31:50 -0500 (EST)
From:   Nicolas Pitre <nico@fluxnic.net>
To:     Masahiro Yamada <masahiroy@kernel.org>
cc:     linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Michal Marek <michal.lkml@markovi.net>,
        linux-doc@vger.kernel.org
Subject: Re: [PATCH 1/2] kconfig: allow symbols implied by y to become m
In-Reply-To: <20200302062340.21453-1-masahiroy@kernel.org>
Message-ID: <nycvar.YSQ.7.76.2003021024370.1559@knanqh.ubzr>
References: <20200302062340.21453-1-masahiroy@kernel.org>
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On Mon, 2 Mar 2020, Masahiro Yamada wrote:

> The 'imply' keyword restricts a symbol to y or n, excluding m
> when it is implied by y. This is the original behavior since
> commit 237e3ad0f195 ("Kconfig: Introduce the "imply" keyword").
> 
> However, the author of the 'imply' keyword, Nicolas Pitre, stated
> that the 'imply' keyword should not impose any restrictions. [1]
> 
> I agree, and want to get rid of this tricky behavior.
> 
> [1]: https://lkml.org/lkml/2020/2/19/714
> 
> Suggested-by: Nicolas Pitre <nico@fluxnic.net>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Acked-by: Nicolas Pitre <nico@fluxnic.net>

In addition to the IS_REACHABLE() note, it might be a good idea to 
suggest adding an "imply" reference to the dependency if the feature 
provided by BAZ is highli desirable, e.g.:

config FOO
	tristate
	imply BAR
	imply BAZ


> ---
> 
>  Documentation/kbuild/kconfig-language.rst | 12 +++++++++++-
>  scripts/kconfig/symbol.c                  |  5 +----
>  2 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index d0111dd26410..d4d988aea679 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -173,7 +173,7 @@ applicable everywhere (see syntax).
>  	===		===		=============	==============
>  	n		y		n		N/m/y
>  	m		y		m		M/y/n
> -	y		y		y		Y/n
> +	y		y		y		Y/m/n
>  	y		n		*		N
>  	===		===		=============	==============
>  
> @@ -181,6 +181,16 @@ applicable everywhere (see syntax).
>    ability to hook into a secondary subsystem while allowing the user to
>    configure that subsystem out without also having to unset these drivers.
>  
> +  Note: If the combination of FOO=y and BAR=m causes a link error,
> +  you can guard the function call with IS_REACHABLE()::
> +
> +	foo_init()
> +	{
> +		if (IS_REACHABLE(CONFIG_BAZ))
> +			baz_register(&foo);
> +		...
> +	}
> +
>  - limiting menu display: "visible if" <expr>
>  
>    This attribute is only applicable to menu blocks, if the condition is
> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
> index 8d38b700b314..b101ef3c377a 100644
> --- a/scripts/kconfig/symbol.c
> +++ b/scripts/kconfig/symbol.c
> @@ -401,8 +401,7 @@ void sym_calc_value(struct symbol *sym)
>  				sym_warn_unmet_dep(sym);
>  			newval.tri = EXPR_OR(newval.tri, sym->rev_dep.tri);
>  		}
> -		if (newval.tri == mod &&
> -		    (sym_get_type(sym) == S_BOOLEAN || sym->implied.tri == yes))
> +		if (newval.tri == mod && sym_get_type(sym) == S_BOOLEAN)
>  			newval.tri = yes;
>  		break;
>  	case S_STRING:
> @@ -484,8 +483,6 @@ bool sym_tristate_within_range(struct symbol *sym, tristate val)
>  		return false;
>  	if (sym->visible <= sym->rev_dep.tri)
>  		return false;
> -	if (sym->implied.tri == yes && val == mod)
> -		return false;
>  	if (sym_is_choice_value(sym) && sym->visible == yes)
>  		return val == yes;
>  	return val >= sym->rev_dep.tri && val <= sym->visible;
> -- 
> 2.17.1
> 
>