netdev - Re: [PATCH net-next 2/6] net: dsa: do not skip -EOPNOTSUPP in dsa_port_vid

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Date:   Fri, 23 Aug 2019 09:23:20 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next 2/6] net: dsa: do not skip -EOPNOTSUPP in
 dsa_port_vid_add

On 8/22/19 4:44 PM, Vladimir Oltean wrote:
> On Fri, 23 Aug 2019 at 02:43, Vivien Didelot <vivien.didelot@...il.com> wrote:
>>
>> Hi Vladimir,
>>
>> On Fri, 23 Aug 2019 01:06:58 +0300, Vladimir Oltean <olteanv@...il.com> wrote:
>>> Hi Vivien,
>>>
>>> On 8/22/19 11:13 PM, Vivien Didelot wrote:
>>>> Currently dsa_port_vid_add returns 0 if the switch returns -EOPNOTSUPP.
>>>>
>>>> This function is used in the tag_8021q.c code to offload the PVID of
>>>> ports, which would simply not work if .port_vlan_add is not supported
>>>> by the underlying switch.
>>>>
>>>> Do not skip -EOPNOTSUPP in dsa_port_vid_add but only when necessary,
>>>> that is to say in dsa_slave_vlan_rx_add_vid.
>>>>
>>>
>>> Do you know why Florian suppressed -EOPNOTSUPP in 061f6a505ac3 ("net:
>>> dsa: Add ndo_vlan_rx_{add, kill}_vid implementation")?
>>> I forced a return value of -EOPNOTSUPP here and when I create a VLAN
>>> sub-interface nothing breaks, it just says:
>>> RTNETLINK answers: Operation not supported
>>> which IMO is expected.
>>
>> I do not know what you mean. This patch does not change the behavior of
>> dsa_slave_vlan_rx_add_vid, which returns 0 if -EOPNOTSUPP is caught.
>>
> 
> Yes, but what's wrong with just forwarding -EOPNOTSUPP?

It makes us fail adding the VLAN to the slave network device, which
sounds silly, if we can't offload it in HW, that's fine, we can still do
a SW VLAN instead, see net/8021q/vlan_core.c::vlan_add_rx_filter_info().

Maybe a more correct solution is to set the NETIF_F_HW_VLAN_CTAG_FILTER
feature bit only if we have the ability to offload, now that I think
about it. Would you want me to cook a patch doing that?
-- 
Florian