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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 3 Feb 2020 13:25:27 +0100
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Subject: Re: [PATCH 2/2] ARM: configs: Cleanup old Kconfig options
To:     Krzysztof Kozlowski <krzk@kernel.org>
Cc:     Joe Perches <joe@perches.com>,
        Russell King <linux@armlinux.org.uk>,
        Alexander Shiyan <shc_work@mail.ru>,
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On Mon, Feb 3, 2020 at 12:53 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>
> On Thu, 30 Jan 2020 at 23:06, Joe Perches <joe@perches.com> wrote:
> >
> > On Thu, 2020-01-30 at 20:55 +0100, Krzysztof Kozlowski wrote:
> > > CONFIG_MMC_BLOCK_BOUNCE is gone since commit c3dccb74be28 ("mmc: core:
> > > Delete bounce buffer Kconfig option").
> > >
> > > CONFIG_LBDAF is gone since commit 72deb455b5ec ("block: remove
> > > CONFIG_LBDAF").
> > >
> > > CONFIG_IOSCHED_DEADLINE and CONFIG_IOSCHED_CFQ are gone since
> > > commit f382fb0bcef4 ("block: remove legacy IO schedulers").
> > >
> > > The IOSCHED_DEADLINE was replaced by MQ_IOSCHED_DEADLINE and it will be
> > > now enabled by default (along with MQ_IOSCHED_KYBER).
> > >
> > > The IOSCHED_BFQ seems to replace IOSCHED_CFQ so select it in configs
> > > previously choosing the latter.
> > >
> > > CONFIG_CROSS_COMPILE is gone since commit f1089c92da79 ("kbuild: remove
> > > CONFIG_CROSS_COMPILE support").

Acked-by: Arnd Bergmann <arnd@arndb.de>

> > Hi Krzysztof.
> >
> > There seems there are a lot more of these unused CONFIG_<foo>
> > symbols in various defconfigs. (just for arm and treewide below)

Feel free to pick any of these symbols and send patches for those.
No need to do it one symbol at a time, but please group them like
Krzysztof has done.

> Nice finding! The trickier point is to nicely remove them because:
> 1. The easiest is 'savedefconfig' but then some valuable options might
> disappear (like recently happened with DEBUG_FS),
> 2. They could be removed in automated way with a script. However in
> such case what about replacements? If some symbol was replaced with
> other (or just renamed), maybe we should enable the other one to
> restore the desired functionality?
> 3. Or maybe let's don't care about keeping defconfigs stable and just
> clean them up automatically.

I don't see a good way to do it automatically. It would be good to check
that we don't remove Kconfig symbols that are still used in defconfig
files without changing those files as well. Cleaning up afterwards also
works, but this always requires manual inspection for each symbol.

     Arnd