netdev - Re: [RFC PATCH net-next 1/2] net: dsa: allow setting port-based QoS priority using tc matchall skbedit

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Date:   Thu, 14 Jan 2021 00:41:28 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Ido Schimmel <idosch@...dia.com>,
        Petr Machata <petrm@...dia.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...dia.com>, f.fainelli@...il.com,
        vivien.didelot@...il.com
Subject: Re: [RFC PATCH net-next 1/2] net: dsa: allow setting port-based QoS
 priority using tc matchall skbedit

On Wed, Jan 13, 2021 at 05:41:38PM +0200, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> In Time Sensitive Networking it is a common and simple use case to
> configure switches to give all traffic from an attached station the same
> priority, without requiring those stations to use VLAN PCP or IP DSCP to
> signal the priority that they want. Many pieces of hardware support this
> feature via a port-based default priority. We can model this in Linux
> through a matchall action on the ingress qdisc of the port, plus a
> skbedit priority action with the desired priority.

The mv88e6xxx has something similar. There is a bit to enable this
feature, as well as the priority the feature should have. I think that
then takes a value in the range of 0 to 4, but i could be remembering
it wrongly.

> +	int	(*port_priority_set)(struct dsa_switch *ds, int port,
> +				     struct dsa_mall_skbedit_tc_entry *skbedit);

The fact we can turn this on/off suggests there should be a way to
disable this in the hardware, when the matchall is removed. I don't
see any such remove support in this patch.

    Andrew