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

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Date:   Tue, 25 Aug 2020 01:02:03 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Kurt Kanzenbach <kurt@...utronix.de>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Po Liu <Po.Liu@....com>
Subject: Re: [PATCH v3 0/8] Hirschmann Hellcreek DSA driver

On Mon, Aug 24, 2020 at 02:31:10PM -0700, Jakub Kicinski wrote:
> On Thu, 20 Aug 2020 10:11:10 +0200 Kurt Kanzenbach wrote:
> > this series adds a DSA driver for the Hirschmann Hellcreek TSN switch
> > IP. Characteristics of that IP:
> > 
> >  * Full duplex Ethernet interface at 100/1000 Mbps on three ports
> >  * IEEE 802.1Q-compliant Ethernet Switch
> >  * IEEE 802.1Qbv Time-Aware scheduling support
> >  * IEEE 1588 and IEEE 802.1AS support
> 
> I don't see anything worth complaining about here, but this is not my
> area of expertise.. 
> 
> DSA and TAPRIO folks - does this look good to you?

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.

Thanks,
-Vladimir