linux-kernel - Re: [PATCH] firewire: mark expected switch fall-throughs

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Date:   Thu, 14 Mar 2019 11:00:38 +0100
From:   Stefan Richter <stefanr@...6.in-berlin.de>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     linux1394-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH] firewire: mark expected switch fall-throughs

(added Cc: Mathieu Malaterre, who sent a patch which is a subset of this)

On Feb 11 Gustavo A. R. Silva wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.
> 
> This patch fixes the following warnings:
> 
> drivers/firewire/core-device.c: In function ‘set_broadcast_channel’:
> drivers/firewire/core-device.c:969:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
>     if (data & cpu_to_be32(1 << 31)) {
>        ^
> drivers/firewire/core-device.c:974:3: note: here
>    case RCODE_ADDRESS_ERROR:
>    ^~~~
> drivers/firewire/core-iso.c: In function ‘manage_channel’:
> drivers/firewire/core-iso.c:308:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
>     if ((data[0] & bit) == (data[1] & bit))
>        ^
> drivers/firewire/core-iso.c:312:3: note: here
>    default:
>    ^~~~~~~
> drivers/firewire/core-topology.c: In function ‘count_ports’:
> drivers/firewire/core-topology.c:69:23: warning: this statement may fall through [-Wimplicit-fallthrough=]
>     (*child_port_count)++;
>     ~~~~~~~~~~~~~~~~~~~^~
> drivers/firewire/core-topology.c:70:3: note: here
>    case SELFID_PORT_PARENT:
>    ^~~~
> 
> Warning level 3 was used: -Wimplicit-fallthrough=3
> 
> Notice that in some cases, the code comment is modified in
> accordance with what GCC is expecting to find.

OK, I looked up
https://gcc.gnu.org/onlinedocs/gcc-8.3.0/gcc/Warning-Options.html#index-Wimplicit-fallthrough
now.  I am loudly sighing and rolling my eyes...  Anyway; the last regex
listed at the Wimplicit-fallthrough=3 bullet point is obviously the one
you are wanting to match.

> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/firewire/core-device.c   | 2 +-
>  drivers/firewire/core-iso.c      | 2 +-
>  drivers/firewire/core-topology.c | 1 +
>  3 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
> index 7c2eed76011e..0c86548fa4a7 100644
> --- a/drivers/firewire/core-device.c
> +++ b/drivers/firewire/core-device.c
> @@ -970,7 +970,7 @@ static void set_broadcast_channel(struct fw_device *device, int generation)
>  				device->bc_implemented = BC_IMPLEMENTED;
>  				break;
>  			}
> -			/* else fall through to case address error */
> +			/* else, fall through - to case address error */
>  		case RCODE_ADDRESS_ERROR:
>  			device->bc_implemented = BC_UNIMPLEMENTED;
>  		}
> diff --git a/drivers/firewire/core-iso.c b/drivers/firewire/core-iso.c
> index 35e784cffc23..7e5c98840b80 100644
> --- a/drivers/firewire/core-iso.c
> +++ b/drivers/firewire/core-iso.c
> @@ -308,7 +308,7 @@ static int manage_channel(struct fw_card *card, int irm_id, int generation,
>  			if ((data[0] & bit) == (data[1] & bit))
>  				continue;
>  
> -			/* 1394-1995 IRM, fall through to retry. */
> +			/* fall through - to retry for 1394-1995 IRM */

If you don't mind, I will apply your patch with a different wording of this
comment:

			/* fall through - It's an 1394-1995 IRM, retry. */

I'll mark my modification to your patch in the signed-off-by-tag.

>  		default:
>  			if (retry) {
>  				retry--;
> diff --git a/drivers/firewire/core-topology.c b/drivers/firewire/core-topology.c
> index 7db234d3fbdd..82c67e900aad 100644
> --- a/drivers/firewire/core-topology.c
> +++ b/drivers/firewire/core-topology.c
> @@ -67,6 +67,7 @@ static u32 *count_ports(u32 *sid, int *total_port_count, int *child_port_count)
>  		switch (port_type) {
>  		case SELFID_PORT_CHILD:
>  			(*child_port_count)++;
> +			/* fall through */
>  		case SELFID_PORT_PARENT:
>  		case SELFID_PORT_NCONN:
>  			(*total_port_count)++;

-- 
Stefan Richter
-======---== --== -===-
http://arcgraph.de/sr/