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Date:   Thu, 3 Jun 2021 16:35:06 +0200
From:   Thierry Reding <treding@nvidia.com>
To:     Dmitry Osipenko <digetx@gmail.com>
CC:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Colin Cross <ccross@android.com>,
        Olof Johansson <olof@lixom.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>
Subject: Re: linux-next: build warning after merge of the tegra tree
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On Thu, Jun 03, 2021 at 05:03:38PM +0300, Dmitry Osipenko wrote:
> 03.06.2021 15:18, Thierry Reding =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> > On Thu, Jun 03, 2021 at 05:01:48AM +0300, Dmitry Osipenko wrote:
> >> 03.06.2021 03:35, Stephen Rothwell =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> >>> Hi all,
> >>>
> >>> After merging the tegra tree, today's linux-next build (x86_64
> >>> allmodconfig) produced this warning:
> >>>
> >>> WARNING: unmet direct dependencies detected for TEGRA210_EMC_TABLE
> >>>   Depends on [n]: MEMORY [=3Dy] && TEGRA_MC [=3Dy] && ARCH_TEGRA_210_=
SOC [=3Dn]
> >>>   Selected by [m]:
> >>>   - TEGRA210_EMC [=3Dm] && MEMORY [=3Dy] && TEGRA_MC [=3Dy] && (ARCH_=
TEGRA_210_SOC [=3Dn] || COMPILE_TEST [=3Dy])
> >>>
> >>> Probably introduced by commit
> >>>
> >>>   08decdd5b448 ("memory: tegra: Enable compile testing for all driver=
s")
> >>>
> >>
> >> Thank you. This is a new warning to me, apparently this case wasn't pr=
eviously tested by kernel build bot.
> >>
> >> Perhaps this should fix it:
> >>
> >> diff --git a/drivers/memory/tegra/Kconfig b/drivers/memory/tegra/Kconf=
ig
> >> index 71bba2345bce..3f2fa7750118 100644
> >> --- a/drivers/memory/tegra/Kconfig
> >> +++ b/drivers/memory/tegra/Kconfig
> >> @@ -47,7 +47,6 @@ config TEGRA124_EMC
> >> =20
> >>  config TEGRA210_EMC_TABLE
> >>  	bool
> >> -	depends on ARCH_TEGRA_210_SOC
> >=20
> > Why not just add a || COMPILE_TEST like we do for TEGRA210_EMC? Because
> > TEGRA210_EMC being pulled in under COMPILE_TEST (and then pulling in
> > TEGRA210_EMC_TABLE which is missing the alternative path) seems to be
> > the root cause for this.
>=20
> The anonymous Kconfig entry is unavailable by default, it can be only
> selected by other entry, IIUC. In our case the TEGRA210_EMC_TABLE is
> selected by TEGRA210_EMC, hence additional dependencies aren't needed
> for TEGRA210_EMC_TABLE.

The code guarded by TEGRA210_EMC_TABLE makes use of some symbols that
are only available if ARCH_TEGRA_210_SOC is also defined. If we don't
list the dependencies via Kconfig this could lead to a problem where
somebody selected TEGRA210_EMC_TABLE without having a dependency on
ARCH_TEGRA_210_SOC, which would then lead to a build error.

If we do represent the dependency in Kconfig, we'll get a warning like
the above during the configuration step and the offending Kconfig option
will end up disabled, and avoid the build failure.

Granted, this could be caught during patch review, and yes, there's not
technically a need to encode this using Kconfig dependencies, but at the
same time there's also no reason not to use the safeguards we have at
our disposal to avoid this in a more automated way.

I'd prefer to stick with the explicit dependency in Kconfig, so I've
updated the patch to match the dependencies to that of TEGRA210_EMC.

Thierry

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