linux-kernel - Re: [PATCH v3 4/6] fbdev: Include <linux/io.h> via <asm/fb.h>

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Date:   Wed, 3 May 2023 10:09:39 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>, linux-arch@...r.kernel.org,
        linux-fbdev@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, arnd@...db.de, deller@....de,
        chenhuacai@...nel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        James.Bottomley@...senpartnership.com,
        linux-m68k@...ts.linux-m68k.org, linux-parisc@...r.kernel.org,
        vgupta@...nel.org, sparclinux@...r.kernel.org, kernel@...0n.name,
        linux-snps-arc@...ts.infradead.org, davem@...emloft.net,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 4/6] fbdev: Include <linux/io.h> via <asm/fb.h>

On Wed, May 3, 2023 at 9:19 AM Javier Martinez Canillas
<javierm@...hat.com> wrote:
> Thomas Zimmermann <tzimmermann@...e.de> writes:
> > Am 02.05.23 um 21:54 schrieb Sam Ravnborg:
> >> On Tue, May 02, 2023 at 03:02:21PM +0200, Thomas Zimmermann wrote:
>
> [...]
>
> >>>   #include <linux/console.h> /* Why should fb driver call console functions? because console_lock() */
> >>>   #include <video/vga.h>
> >>>
> >>> +#include <asm/fb.h>
> >>
> >> When we have a header like linux/fb.h - it is my understanding that it is
> >> preferred to include that file, and not the asm/fb.h variant.
> >>
> >> This is assuming the linux/fb.h contains the generic stuff, and includes
> >> asm/fb.h for the architecture specific parts.
> >>
> >> So drivers will include linux/fb.h and then they automatically get the
> >> architecture specific parts from asm/fb.h.
> >>
> >> In other words, drivers are not supposed to include asm/fb.h, if
> >> linux.fb.h exists - and linux/fb.h shall include the asm/fb.h.
> >>
> >> If the above holds true, then it is wrong and not needed to add asm/fb.h
> >> as seen above.
> >>
> >>
> >> There are countless examples where the above are not followed,
> >> but to my best understanding the above it the preferred way to do it.
> >
> > Where did youher this? I only know about this in the case of asm/io.h
> > vs. linux/io.h.
> >
>
> I understand that's the case too. I believe even checkpatch.pl complains
> about it? (not that the script always get right, but just as an example).

One more to chime in: in general, drivers should only include <linux/foo.h>.
Including <asm/foo.h> directly is the exception.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds