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

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Message-ID: <CA+h21hpzSNZTK6-wQJkJCC9vs0hao12_tpQRLM5JLXXD_26c_w@mail.gmail.com>
Date:   Fri, 23 Aug 2019 19:32:15 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        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

Hi Florian,

On Fri, 23 Aug 2019 at 19:23, Florian Fainelli <f.fainelli@...il.com> wrote:
>
> 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?

sja1105 doesn't support offloading NETIF_F_HW_VLAN_CTAG_FILTER even
though it does support programming VLANs.
Adding an offloaded VLAN sub-interface on a standalone switch port
(vlan_filtering=0, uses dsa_8021q) would make the driver insert a VLAN
entry whilst the TPID is ETH_P_DSA_8021Q.
Maybe just let the driver set the netdev features, similar to how it
does for the number of TX queues?

> --
> Florian

Regards,
-Vladimir