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

From: Vladimir Oltean <olteanv@gmail.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.