netdev - Re: [PATCH net-next] sfc: support offloading TC VLAN push/pop actions to the MAE

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Date:   Tue, 21 Feb 2023 20:32:13 +0000
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Leon Romanovsky <leon@...nel.org>, edward.cree@....com
Cc:     linux-net-drivers@....com, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, edumazet@...gle.com, netdev@...r.kernel.org,
        habetsm.xilinx@...il.com
Subject: Re: [PATCH net-next] sfc: support offloading TC VLAN push/pop actions
 to the MAE

On 19/02/2023 09:21, Leon Romanovsky wrote:
> On Thu, Feb 16, 2023 at 04:04:42PM +0000, edward.cree@....com wrote:
>> From: Edward Cree <ecree.xilinx@...il.com>
>>
>> EF100 can pop and/or push up to two VLAN tags.
>>
>> Signed-off-by: Edward Cree <ecree.xilinx@...il.com>
...
>> +	/* Translate vlan actions from bitmask to count */
>> +	switch (act->vlan_push) {
>> +	case 0:
>> +	case 1:
>> +		vlan_push = act->vlan_push;
>> +		break;
>> +	case 2: /* can't happen */
> 
> There is no need in case here as "default" will catch.
> 
>> +	default:
>> +		return -EINVAL;
>> +	case 3:
>> +		vlan_push = 2;
>> +		break;
>> +	}
>> +	switch (act->vlan_pop) {
>> +	case 0:
>> +	case 1:
>> +		vlan_pop = act->vlan_pop;
>> +		break;
>> +	case 2: /* can't happen */
>> +	default:
>> +		return -EINVAL;
> 
> Please rely switch-case semantics and don't put default in the middle.

It's legal C and as far as I can tell there's nothing in coding-style.rst
 about it; I did it this way so as to put the cases in the logical(?)
 ascending order and try to make the code self-document the possible
 values of the act-> fields.
Arguably it's the 'default:' rather than the 'case 2:' that's unnecessary
 as the switch argument is an unsigned:2 bitfield, so it can only take on
 these four values.
Although on revisiting this code I wonder if it makes more sense just to
 use the 'count' (rather than 'bitmask') form throughout, including in
 act->vlan_push/pop; it makes the tc.c side of the code slightly more
 involved, but gets rid of this translation entirely.  WDYT?

-ed