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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 19 Feb 2020 10:54:02 +0100
Message-ID: <CAMuHMdWNhd3kwqQ2OYOscq3VFDjip_FZtt8w6PVCenz095kCZg@mail.gmail.com>
Subject: Re: [PATCH] kconfig: make 'imply' obey the direct dependency
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     linux-kbuild <linux-kbuild@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Nicolas Pitre <nico@fluxnic.net>,
        Richard Cochran <richardcochran@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Mark Brown <broonie@kernel.org>,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Michal Marek <michal.lkml@markovi.net>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Yamada-san,

On Wed, Feb 19, 2020 at 10:24 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> On Wed, Feb 19, 2020 at 5:42 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Wed, Feb 19, 2020 at 8:51 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > The 'imply' statement may create unmet direct dependency when the
> > > implied symbol depends on m.
> > >
> > > [Test Code]
> > >
> > >   config FOO
> > >           tristate "foo"
> > >           imply BAZ
> > >
> > >   config BAZ
> > >           tristate "baz"
> > >           depends on BAR
> > >
> > >   config BAR
> > >           def_tristate m
> > >
> > >   config MODULES
> > >           def_bool y
> > >           option modules
> > >
> > > If you set FOO=y, BAZ is also promoted to y, which results in the
> > > following .config file:
> > >
> > >   CONFIG_FOO=y
> > >   CONFIG_BAZ=y
> > >   CONFIG_BAR=m
> > >   CONFIG_MODULES=y
> > >
> > > This ignores the dependency "BAZ depends on BAR".
> > >
> > > Unlike 'select', what is worse, Kconfig never shows the
> > > "WARNING: unmet direct dependencies detected for ..." for this case.
> > >
> > > Because 'imply' should be weaker than 'depends on', Kconfig should
> > > take the direct dependency into account.
> > >
> > > Describe this case in Documentation/kbuild/kconfig-language.rst for
> > > clarification.
> > >
> > > Commit 237e3ad0f195 ("Kconfig: Introduce the "imply" keyword") says that
> > > a symbol implied by y is restricted to y or n, excluding m.
> > >
> > > As for the combination of FOO=y and BAR=m, the case of BAZ=m is excluded
> > > by the 'imply', and BAZ=y is also excluded by 'depends on'. So, only the
> > > possible value is BAZ=n.
> > >
> > > Having said that, this case was probably "We don't care" at that time
> > > because Kconfig did not handle 'depends on m' correctly until
> > > commit f622f8279581 ("kconfig: warn unmet direct dependency of tristate
> > > symbols selected by y") fixed it.
> > >
> > > Backporting this to 4.19+ will probably be fine. If you care this
> > > problem on 4.14.x, you need to backport f622f8279581 as well.
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> >
> > Thanks a lot! This fixes the build issues in
> > https://lore.kernel.org/alsa-devel/CAMuHMdW8SvDgQJyenTtEm4Xn2Ma6PK9pfwKR2_gn60t2AqNWXg@mail.gmail.com/
> >
> > Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> Even if this patch fixes the build issues,
> the result may not be what you expect.
>
> The very subtle part of 'imply' is that
> symbols implied by 'y' cannot be 'm'.
>
> When CONFIG_SND_SOC_ALL_CODECS=y,
> the select'ed drivers were previously able to be 'm'.
>
> After ea00d95200d02, drivers that were previously
> 'm' are now 'n'.
>
> Probably, it shrunk the test-coverage.
>
> I'd recommend to compare the .config file.

I always do, when running make oldconfig ;-)

I only see expected changes from y to m.
I don't see any unexpected changes from m to n.
I do see a few unexpected "CONFIG_<foo> is not set" that are no longer
suppressed.

--- .config.orig        2020-02-19 09:26:41.411812042 +0100
+++ .config     2020-02-19 09:28:05.143822097 +0100
@@ -1193,7 +1193,7 @@
 CONFIG_REGMAP=y
 CONFIG_REGMAP_AC97=y
 CONFIG_REGMAP_I2C=y
-CONFIG_REGMAP_SLIMBUS=y
+CONFIG_REGMAP_SLIMBUS=m
 CONFIG_REGMAP_SPI=y
 CONFIG_REGMAP_MMIO=y
 CONFIG_REGMAP_IRQ=y
@@ -5235,7 +5235,7 @@
 CONFIG_SND_SOC_UDA1334=y
 CONFIG_SND_SOC_UDA134X=y
 CONFIG_SND_SOC_UDA1380=y
 CONFIG_SND_SOC_WCD934X=m
 CONFIG_SND_SOC_WL1273=y
 CONFIG_SND_SOC_WM0010=y
@@ -5017,6 +5017,7 @@
 CONFIG_SND_SOC_ARIZONA=y
 CONFIG_SND_SOC_WM_HUBS=y
 CONFIG_SND_SOC_WM_ADSP=y
+# CONFIG_SND_SOC_AB8500_CODEC is not set
 CONFIG_SND_SOC_AC97_CODEC=y
 CONFIG_SND_SOC_AD1836=y
 CONFIG_SND_SOC_AD193X=y
@@ -5085,6 +5086,7 @@
 CONFIG_SND_SOC_CS4341=y
 CONFIG_SND_SOC_CS4349=y
 CONFIG_SND_SOC_CS47L15=y
+# CONFIG_SND_SOC_CS47L24 is not set
 CONFIG_SND_SOC_CS47L35=y
 CONFIG_SND_SOC_CS47L85=y
 CONFIG_SND_SOC_CS47L90=y
@@ -5117,6 +5119,7 @@
 CONFIG_SND_SOC_INNO_RK3036=y
 CONFIG_SND_SOC_ISABELLE=y
 CONFIG_SND_SOC_LM49453=y
+# CONFIG_SND_SOC_LOCHNAGAR_SC is not set
 CONFIG_SND_SOC_MADERA=y
 CONFIG_SND_SOC_MAX98088=y
 CONFIG_SND_SOC_MAX98090=y
@@ -5228,11 +5231,12 @@
 CONFIG_SND_SOC_TSCS42XX=y
 CONFIG_SND_SOC_TSCS454=y
 CONFIG_SND_SOC_TWL4030=y
+# CONFIG_SND_SOC_TWL6040 is not set
 CONFIG_SND_SOC_UDA1334=y
 CONFIG_SND_SOC_UDA134X=y
 CONFIG_SND_SOC_UDA1380=y
-CONFIG_SND_SOC_WCD9335=y
-CONFIG_SND_SOC_WCD934X=y
+CONFIG_SND_SOC_WCD9335=m
+CONFIG_SND_SOC_WCD934X=m
 CONFIG_SND_SOC_WL1273=y
 CONFIG_SND_SOC_WM0010=y
 CONFIG_SND_SOC_WM1250_EV1=y
@@ -5241,6 +5245,8 @@
 CONFIG_SND_SOC_WM5100=y
 CONFIG_SND_SOC_WM5102=m
 CONFIG_SND_SOC_WM5110=y
+# CONFIG_SND_SOC_WM8350 is not set
+# CONFIG_SND_SOC_WM8400 is not set
 CONFIG_SND_SOC_WM8510=y
 CONFIG_SND_SOC_WM8523=y
 CONFIG_SND_SOC_WM8524=y
@@ -5293,7 +5299,7 @@
 CONFIG_SND_SOC_MAX9768=y
 CONFIG_SND_SOC_MAX9877=y
 # CONFIG_SND_SOC_DUMMY is not set
-CONFIG_SND_SOC_MC13783=y
+CONFIG_SND_SOC_MC13783=m
 CONFIG_SND_SOC_ML26124=y
 CONFIG_SND_SOC_MT6351=y
 CONFIG_SND_SOC_MT6358=y
@@ -5899,6 +5905,7 @@
 # CONFIG_COMMON_CLK_MT8516 is not set
 # end of Clock driver for MediaTek SoC

+# CONFIG_COMMON_CLK_AXG_AUDIO is not set
 CONFIG_QCOM_GDSC=y
 CONFIG_COMMON_CLK_QCOM=m
 CONFIG_QCOM_A53PLL=m

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds