netdev - Re: [PATCH v3 0/8] Hirschmann Hellcreek DSA driver

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Date:   Mon, 24 Aug 2020 15:35:18 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     kuba@...nel.org, kurt@...utronix.de, andrew@...n.ch,
        vivien.didelot@...il.com, f.fainelli@...il.com,
        netdev@...r.kernel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, bigeasy@...utronix.de,
        richardcochran@...il.com, kamil.alkhouri@...offenburg.de,
        ilias.apalodimas@...aro.org, ivan.khoronzhuk@...aro.org,
        vinicius.gomes@...el.com, xiaoliang.yang_1@....com, Po.Liu@....com
Subject: Re: [PATCH v3 0/8] Hirschmann Hellcreek DSA driver

From: Vladimir Oltean <olteanv@...il.com>
Date: Tue, 25 Aug 2020 01:02:03 +0300

> Just my comment on patch 5/8 about netdev->tc_to_txq. There are 2
> distinct things about that:
> - accessing struct net_device directly hurts the DSA model a little bit.
> - I think there's some confusion regarding the use of netdev->tc_to_txq
>   itself. I don't think that's the right place to setup a VLAN PCP to
>   traffic class mapping. That's simply "what traffic class does each
>   netdev queue have". I would even go as far as say that Linux doesn't
>   support a VLAN PCP to TC mapping (similar to the DSCP to TC mapping
>   from the DCB ops) at all, except for the ingress-qos-map and
>   egress-qos-map of the 8021q driver, which can't be offloaded and don't
>   map nicely over existing hardware anyway (what hardware has an
>   ingress-qos-map and an egress-qos-map per individual VLAN?!).
>   Although I do really see the need for having a mapping between VLAN
>   PCP and traffic class, I would suggest Kurt to not expose this through
>   taprio/mqprio (hardcode the PCP mapping as 1-to-1 with TC, as other
>   drivers do), and let's try to come up separately with an abstraction
>   for that.

Agreed, Kurt can you repost this series without the TAPRIO support for
now since it's controversial and needs more discussion and changes?

Thank you.