linux-kernel - Re: [GIT PULL] RESEND: thermal for v5.9-rc1

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Date:   Fri, 7 Aug 2020 08:54:24 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Colin King <colin.king@...onical.com>,
        Shawn Guo <shawn.guo@...aro.org>,
        Lukasz Luba <Lukasz.Luba@....com>,
        Sumeet Pawnikar <sumeet.r.pawnikar@...el.com>,
        Henry Yen <henry.yen@...iatek.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM mailing list <linux-pm@...r.kernel.org>,
        Marian-Cristian Rotariu 
        <marian-cristian.rotariu.rb@...renesas.com>
Subject: Re: [GIT PULL] RESEND: thermal for v5.9-rc1

On Fri, Aug 7, 2020 at 2:40 AM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>
> It defaults to 'y' because the previous (but unused) implementation was
> unconditionally compiled-in and because of the thermal users needs.
>
> Is default=y wrong given this history?

One million percent wrong.

The fact that the old implementation was never used just shows that
it's not so important, and it shouldn't be default 'y'. Not having it
doesn't break anything.

And the new implementation presumably isn't even compatible with the
old format also means that it shouldn't be default 'y'. Building it in
wouldn't help anyway.

And the fact that _some_ users might want it does not mean that it
should be default 'y', because those users presumably _know_ they want
it.

IOW, defaulting to 'y' is just wrong in every possible way. This is
not some kind of "to maintain compatibility and not break existing
users we should enable this" kind of thing.

And it's not some kind of "everybody should have it" thing either,
since presumably nobody has the user-space support for it anyway.

It's something that a new distro would enable _if_ they actually end
up supporting the user space. Not something the kernel should enable
"just because".

Really: "default y" is _wrong_. Every developer thinks that _their_
code is so magical and special that everybody should run it.

And every developer is almost always wrong. Unless you have a "not
having this will break existing users", you don't do it.

                 Linus