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 02:17:59 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
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 Thu, Jan 14, 2021 at 12:41:28AM +0100, Andrew Lunn wrote:
> On Wed, Jan 13, 2021 at 05:41:38PM +0200, Vladimir Oltean wrote:
> > +	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.

I don't understand this comment, sorry. When the matchall filter
containing the skbedit action gets removed, DSA calls the driver's
.port_priority_set callback again, this time with a priority of 0.
There's nothing to "remove" about a port priority. I made an assumption
(which I still consider perfectly reasonable) that no port-based
prioritization means that all traffic gets classified to traffic class 0.