linux-kernel - Re: [PATCH 18/22] tty: mips_ejtag_fdc: Mark expected switch fall-through

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Date:   Tue, 10 Mar 2020 04:06:03 +0300
From:   Sergey Semin <Sergey.Semin@...kalelectronics.ru>
To:     Jiri Slaby <jslaby@...e.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/22] tty: mips_ejtag_fdc: Mark expected switch
 fall-through

On Mon, Mar 09, 2020 at 05:12:40PM +0100, Jiri Slaby wrote:
> On 06. 03. 20, 13:47, Sergey.Semin@...kalelectronics.ru wrote:
> > From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > 
> > Mark mips_ejtag_fdc_encode() methods switch-case-4 as expecting to
> > fall through.
> > 
> > This patch fixes the following warning:
> > 
> > drivers/tty/mips_ejtag_fdc.c: In function ‘mips_ejtag_fdc_encode’:
> > drivers/tty/mips_ejtag_fdc.c:245:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
> >    word.word &= 0x00ffffff;
> >    ~~~~~~~~~~^~~~~~~~~~~~~
> > drivers/tty/mips_ejtag_fdc.c:246:2: note: here
> >   case 3:
> >   ^~~~
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > Signed-off-by: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> > Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> > Cc: Paul Burton <paulburton@...nel.org>
> > Cc: Ralf Baechle <ralf@...ux-mips.org>
> > ---
> >  drivers/tty/mips_ejtag_fdc.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/tty/mips_ejtag_fdc.c b/drivers/tty/mips_ejtag_fdc.c
> > index 620d8488b83e..21e76a2ec182 100644
> > --- a/drivers/tty/mips_ejtag_fdc.c
> > +++ b/drivers/tty/mips_ejtag_fdc.c
> > @@ -243,6 +243,7 @@ static struct fdc_word mips_ejtag_fdc_encode(const char **ptrs,
> >  		/* Fall back to a 3 byte encoding */
> >  		word.bytes = 3;
> >  		word.word &= 0x00ffffff;
> > +		/* Fall through */
> 
> We now have "fallthrough;", so I believe you should use that instead of
> comments.
> 

Hello Jiri,

Thanks for the comment. I didn't know about that new macro. Since Greg
already pulled this patch in his tty-next branch, I won't send an
update in the next patchset revision. But I'll certainly remember that
there is a specific macro to fix the fallthrough warning in the kernel
and will use it next time I find the same problem someplace else.

Regards,
-Sergey

> thanks,
> -- 
> js
> suse labs