linux-kernel - Re: [PATCH] m68k: atari: Make Atari ROM port I/O write macros return void

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Message-ID: <CAMuHMdX3EYrGPPUEZ3_YPyr6zHnV-xEW3mYB_QyFYaqg_grF-w@mail.gmail.com>
Date:   Fri, 20 May 2022 17:07:56 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] m68k: atari: Make Atari ROM port I/O write macros return void

Hi Günter,

On Fri, May 20, 2022 at 4:52 PM Guenter Roeck <linux@...ck-us.net> wrote:
> On 5/20/22 07:32, Geert Uytterhoeven wrote:
> > The macros implementing Atari ROM port I/O writes do not cast away their
> > output, unlike similar implementations for other I/O buses.
> > When they are combined using conditional expressions in the definitions of
> > outb() and friends, this triggers sparse warnings like:
> >
> >      drivers/net/appletalk/cops.c:382:17: error: incompatible types in conditional expression (different base types):
> >      drivers/net/appletalk/cops.c:382:17:    unsigned char
> >      drivers/net/appletalk/cops.c:382:17:    void
> >
> > Fix this by adding casts to "void".
> >
> > Reported-by: kernel test robot <lkp@...el.com>
> > Reported-by: Guenter Roeck <linux@...ck-us.net>
> > Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>

Thanks!

> > Removing the casts instead causes issues with functions propagating void
> > return values (return expression in void function), which BTW sparse
> > complains about, too.
>
> We live and learn. I didn't even know that this was valid syntax.

I knew about the syntax, but didn't realize immediately why it was
done that way.

Initially I thought it was some relic from the "always cast to void
to make it clear you do not care about the return value"-frenzy, which
are inside Linux visible mostly in the various "(void)acpi_<foo>(...);"
calls.  AFAIK these are checked by some external tools.
In Linux, we have __must_check to annotate the important cases.

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