linux-kernel - Re: [PATCH] USB: serial: io_edgeport: mark expected switch fall-throughs

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Date:   Mon, 2 Jul 2018 10:51:00 +0200
From:   Johan Hovold <johan@...nel.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: io_edgeport: mark expected switch
 fall-throughs

On Thu, Jun 28, 2018 at 01:40:30PM -0500, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch cases
> where we are expecting to fall through.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/usb/serial/io_edgeport.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
> index 97c69d3..441dab6 100644
> --- a/drivers/usb/serial/io_edgeport.c
> +++ b/drivers/usb/serial/io_edgeport.c
> @@ -1760,7 +1760,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
>  				edge_serial->rxState = EXPECT_HDR2;
>  				break;
>  			}
> -			/* otherwise, drop on through */
> +			/* else: fall through */

This doesn't silence the compiler warning with gcc 7.2.0 as the "else: "
pattern isn't recognised.

>  		case EXPECT_HDR2:
>  			edge_serial->rxHeader2 = *buffer;
>  			++buffer;
> @@ -1820,7 +1820,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
>  					edge_serial->rxState = EXPECT_DATA;
>  					break;
>  				}
> -				/* Else, drop through */
> +				/* else: fall through */
>  			}

And this doesn't work either due to the "else: " as well as the fact
that the compiler expects the fallthrough comment to precede the case
statement directly (e.g. it would need to be moved out of the else
block, but that isn't necessarily desirable as we discussed last year: 

	lkml.kernel.org/r/20171027203906.GA7054@...eddedor.com

)

>  		case EXPECT_DATA: /* Expect data */
>  			if (bufferLength < edge_serial->rxBytesRemaining) {

How do you compile test these these patches?

Thanks,
Johan