linux-kernel - Re: [PATCH] media: staging: omap4iss: Include asm/cacheflush.h after generic includes

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Message-ID: <CA+55aFwVVQcbpH=3Qf8hfGhx_Dz-Xp0N+gbAoaFhqLkVD-+WtA@mail.gmail.com>
Date:   Tue, 24 Jul 2018 11:48:19 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     mchehab+samsung@...nel.org
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Staging subsystem List <devel@...verdev.osuosl.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] media: staging: omap4iss: Include asm/cacheflush.h after
 generic includes

On Tue, Jul 24, 2018 at 11:39 AM Mauro Carvalho Chehab
<mchehab+samsung@...nel.org> wrote:
>
> Works for me. Do you intend to apply it directly?

Yes, I took it and it should be pushed out.

> Yeah, some time ago mailing lists got flooded with some janitorial's
> patchset adding includes (some claiming to be needed on some archs or
> under some random Kconfigs)... Compile-test ended by adding more such
> stuff (for a good reason, IMHO). I wonder if are there a better way to
> handle includes without slowing builds.

It's a nightmare to do by hand, with all the different architectures
having slightly different header file requirements.

The scheduler people did it last year (roughly Feb-2017 timeframe),
and it was painful and involved a lot of build testing. Basically some
<linux/sched.h> was split up into <linux/sched/*.h>

I wouldn't encourage people to do that again without some tooling to
actually look at "what symbols might get defined by header file
collection XYZ, what symbols might I need with any config option" kind
of logic.

But it would be lovely if somebody *could* do tooling like that.

Just having something you can run on C files that says "these headers
are completely unused under all possibly config options and
architectures" might be interesting.

Because right now, most people tend to just copy a big set of headers,
whether they need it or not. And they almost never shrink, but new
ones get added as people add uses.

            Linus