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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sat, 30 Oct 2021 00:05:28 +0200
Message-ID: <CAK8P3a1L8x48ZGhFKaMNa0MXCGrouw2EEwe9uo640bnnf=4dOA@mail.gmail.com>
Subject: Re: [PATCH] ARM: fix unmet dependency on BITREVERSE for HAVE_ARCH_BITREVERSE
To:     Julian Braha <julianbraha@gmail.com>
Cc:     Russell King - ARM Linux <linux@armlinux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Mark Rutland <mark.rutland@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        fazilyildiran@gmail.com
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On Fri, Oct 29, 2021 at 10:31 PM Julian Braha <julianbraha@gmail.com> wrote:
>
> When ARM is enabled, and BITREVERSE is disabled,
> Kbuild gives the following warning:
>
> WARNING: unmet direct dependencies detected for HAVE_ARCH_BITREVERSE
>   Depends on [n]: BITREVERSE [=n]
>   Selected by [y]:
>   - ARM [=y] && (CPU_32v7M [=n] || CPU_32v7 [=y]) && !CPU_32v6 [=n]
>
> This is because ARM selects HAVE_ARCH_BITREVERSE
> without selecting BITREVERSE, despite
> HAVE_ARCH_BITREVERSE depending on BITREVERSE.
>
> This unmet dependency bug was found by Kismet,
> a static analysis tool for Kconfig. Please advise if this
> is not the appropriate solution.
>
> Signed-off-by: Julian Braha <julianbraha@gmail.com>

This works, but I think it would be better handled differently:

The other 'select BITREVERSE' instances are for drivers that use
bitrever(), not those that provide it.

We can probably just remove the dependency. Alternatively we could
change arch/arm/ to

     select HAVE_ARCH_BITREVERSE if BITREVERSE && ((CPU_32v7M ||
CPU_32v7) && !CPU_32v6)

Regardless of what we do here, note that

a) the 'select' lines in CONFIG_ARM are sorted alphabetically, and
   should be kept that way

b) the same probably exists on arch/mips and arch/arm64, whatever we
   do here should be the same as on the other architectures.

        Arnd