linux-kernel - Re: [PATCH net-next] amd-xgbe: Mark expected switch fall-throughs

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Date:   Thu, 25 Apr 2019 09:54:22 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH net-next] amd-xgbe: Mark expected switch fall-throughs

Hi,

On 4/25/19 8:12 AM, Lendacky, Thomas wrote:
[..]
>>   ^~~~
>>
>> Warning level 3 was used: -Wimplicit-fallthrough=3
>>
>> Notice that, in this particular case, the code comments are modified
>> in accordance with what GCC is expecting to find.
>>
>> This patch is part of the ongoing efforts to enable
>> -Wimplicit-fallthrough.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>> ---
>>  drivers/net/ethernet/amd/xgbe/xgbe-drv.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
>> index 0cc911f928b1..3dd0cecddba8 100644
>> --- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
>> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
>> @@ -1612,7 +1612,7 @@ static int xgbe_set_hwtstamp_settings(struct xgbe_prv_data *pdata,
>>  	/* PTP v2, UDP, any kind of event packet */
>>  	case HWTSTAMP_FILTER_PTP_V2_L4_EVENT:
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSVER2ENA, 1);
>> -	/* PTP v1, UDP, any kind of event packet */
>> +		/* Fall through - to PTP v1, UDP, any kind of event packet */
> 
> If the compiler doesn't have a problem with adding just an indented
> "Fall through" comment and leaving the original comment in place, I would
> prefer that. It seems clearer to me.
> 

This is the other alternative:

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
index 0cc911f928b1..f913bf404baa 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
@@ -1613,6 +1613,7 @@ static int xgbe_set_hwtstamp_settings(struct xgbe_prv_data *pdata,
        case HWTSTAMP_FILTER_PTP_V2_L4_EVENT:
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSVER2ENA, 1);
        /* PTP v1, UDP, any kind of event packet */
+               /* Fall through */
        case HWTSTAMP_FILTER_PTP_V1_L4_EVENT:
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV4ENA, 1);
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV6ENA, 1);
@@ -1624,6 +1625,7 @@ static int xgbe_set_hwtstamp_settings(struct xgbe_prv_data *pdata,
        case HWTSTAMP_FILTER_PTP_V2_L4_SYNC:
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSVER2ENA, 1);
        /* PTP v1, UDP, Sync packet */
+               /* Fall through */
        case HWTSTAMP_FILTER_PTP_V1_L4_SYNC:
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV4ENA, 1);
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV6ENA, 1);
@@ -1635,6 +1637,7 @@ static int xgbe_set_hwtstamp_settings(struct xgbe_prv_data *pdata,
        case HWTSTAMP_FILTER_PTP_V2_L4_DELAY_REQ:
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSVER2ENA, 1);
        /* PTP v1, UDP, Delay_req packet */
+               /* Fall through */
        case HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ:
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV4ENA, 1);
                XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV6ENA, 1);


The thing is that the fall-through comments have to be placed at the
very bottom of each case.

Which do you prefer?

Thanks
--
Gustavo

> Thanks,
> Tom
> 
>>  	case HWTSTAMP_FILTER_PTP_V1_L4_EVENT:
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV4ENA, 1);
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV6ENA, 1);
>> @@ -1623,7 +1623,7 @@ static int xgbe_set_hwtstamp_settings(struct xgbe_prv_data *pdata,
>>  	/* PTP v2, UDP, Sync packet */
>>  	case HWTSTAMP_FILTER_PTP_V2_L4_SYNC:
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSVER2ENA, 1);
>> -	/* PTP v1, UDP, Sync packet */
>> +		/* Fall through - to PTP v1, UDP, Sync packet */
>>  	case HWTSTAMP_FILTER_PTP_V1_L4_SYNC:
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV4ENA, 1);
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV6ENA, 1);
>> @@ -1634,7 +1634,7 @@ static int xgbe_set_hwtstamp_settings(struct xgbe_prv_data *pdata,
>>  	/* PTP v2, UDP, Delay_req packet */
>>  	case HWTSTAMP_FILTER_PTP_V2_L4_DELAY_REQ:
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSVER2ENA, 1);
>> -	/* PTP v1, UDP, Delay_req packet */
>> +		/* Fall through - to PTP v1, UDP, Delay_req packet */
>>  	case HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ:
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV4ENA, 1);
>>  		XGMAC_SET_BITS(mac_tscr, MAC_TSCR, TSIPV6ENA, 1);
>>