linux-kernel - Bogus dependency for HW_RANDOM

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Date:   Tue, 10 Dec 2019 14:41:04 +0000
From:   Alyssa Ross <hi@...ssa.is>
To:     linux-kernel@...r.kernel.org
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kbuild@...r.kernel.org, linux-crypto@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Bogus dependency for HW_RANDOM_VIRTIO with oldconfig

I'm new here and not sure if I'm contacting the correct people/groups --
please point me in the right direction if not.  I don't know if the
culprit here is Kconfig, the virtio Kconfig file, the hw_random Kconfig
file, or some combination of those.

I believe I have discovered an issue with the order in which make
oldconfig asks for virtio-related options, and would appreciate some
advice on how to solve it:

HW_RANDOM_VIRTIO=y depends on VIRTIO=y.  In my kernel, VIRTIO=y is
selected by VIRITO_PCI=y, but when make oldconfig prompts for
HW_RANDOM_VIRTIO, VIRTIO_PCI has not been prompted for yet, and so
VIRTIO is still set to m.

This means that it's not possible for me to set HW_RANDOM_VIRTIO=y using
oldconfig without setting an VIRTIO-selecting option I don't need, but
that is prompted for _before_ HW_RANDOM_VIRTIO.  One such option that I
have identified so far is VOP.  It is prompted for before
HW_RANDOM_VIRTIO, and so if I set VOP=y it is now possible to set
HW_RANDOM_VIRTIO.

When using menuconfig on a config file generated with oldconfig, that
does not have HW_RANDOM_VIRTIO enabled, I am able to set HW_RANDOM=y and
HW_RANDOM_VIRTIO=y, and after saving I can confirm that no other changes
have been made to the configuration file.  This tells me that there's no
need for a dependency on e.g. VOP, except when using oldconfig.

So, I think there is an ordering issue here, and that oldconfig
should not prompt for HW_RANDOM_VIRTIO until after any option that might
select VIRTIO=y.

I would be happy to try to submit or test a patch to fix this, but I
don't know where to go from here.