On Sat, Oct 30, 2021 at 12:05:28AM +0200, Arnd Bergmann wrote:

On Fri, Oct 29, 2021 at 10:31 PM Julian Braha [off-list ref] wrote:

quoted

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 <redacted>

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.

I think HAVE_ARCH_BITREVERSE shouldn't depend on BITREVERSE.
BITREVERSE is set when something wants the bitreverse support.
HAVE_ARCH_BITREVERSE means that the architecture has support for
the bitreverse instructions and the generic code should not be
compiled.

I don't see any reason for HAVE_ARCH_BITREVERSE to depend on
BITREVERSE.

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