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Date:   Wed, 8 Apr 2020 17:17:47 -0400 (EDT)
From:   Nicolas Pitre <nico@fluxnic.net>
To:     Arnd Bergmann <arnd@arndb.de>
cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Andrzej Hajda <a.hajda@samsung.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        "David S. Miller" <davem@davemloft.net>,
        Saeed Mahameed <saeedm@mellanox.com>,
        Leon Romanovsky <leon@kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
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Subject: Re: [RFC 0/6] Regressions for "imply" behavior change
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On Wed, 8 Apr 2020, Arnd Bergmann wrote:

> On Wed, Apr 8, 2020 at 10:38 PM Nicolas Pitre <nico@fluxnic.net> wrote:
> > On Wed, 8 Apr 2020, Arnd Bergmann wrote:
> > > I have created workarounds for the Kconfig files, which now stop using
> > > imply and do something else in each case. I don't know whether there was
> > > a bug in the kconfig changes that has led to allowing configurations that
> > > were not meant to be legal even with the new semantics, or if the Kconfig
> > > files have simply become incorrect now and the tool works as expected.
> >
> > In most cases it is the code that has to be fixed. It typically does:
> >
> >         if (IS_ENABLED(CONFIG_FOO))
> >                 foo_init();
> >
> > Where it should rather do:
> >
> >         if (IS_REACHABLE(CONFIG_FOO))
> >                 foo_init();
> >
> > A couple of such patches have been produced and queued in their
> > respective trees already.
> 
> I try to use IS_REACHABLE() only as a last resort, as it tends to
> confuse users when a subsystem is built as a module and already
> loaded but something relying on that subsystem does not use it.

Then this is a usage policy issue, not a code correctness issue.

The correctness issue is fixed with IS_REACHABLE(). If you want to 
enforce a usage policy then this goes in Kconfig.

But you still can do both.


Nicolas