linux-kernel - Re: [net-next RFC PATCH 0/6] Add support for qca8k mdio rw in Ethernet packet

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Date:   Wed, 8 Dec 2021 02:04:32 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Ansuel Smith <ansuelsmth@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [net-next RFC PATCH 0/6] Add support for qca8k mdio rw in
 Ethernet packet

On Wed, Dec 08, 2021 at 01:47:36AM +0200, Vladimir Oltean wrote:
> > 2) is harder. But as far as i know, we have an 1:N setup.  One switch
> > driver can use N tag drivers. So we need the switch driver to be sure
> > the tag driver is what it expects. We keep the shared state in the tag
> > driver, so it always has valid data, but when the switch driver wants
> > to get a pointer to it, it needs to pass a enum dsa_tag_protocol and
> > if it does not match, the core should return -EINVAL or similar.
> 
> In my proposal, the tagger will allocate the memory from its side of the
> ->connect() call. So regardless of whether the switch driver side
> connects or not, the memory inside dp->priv is there for the tagger to
> use. The switch can access it or it can ignore it.

I don't think I actually said something useful here.

The goal would be to minimize use of dp->priv inside the switch driver,
outside of the actual ->connect() / ->disconnect() calls.
For example, in the felix driver which supports two tagging protocol
drivers, I think these two methods would be enough, and they would
replace the current felix_port_setup_tagger_data() and
felix_port_teardown_tagger_data() calls.

An additional benefit would be that in ->connect() and ->disconnect() we
get the actual tagging protocol in use. Currently the felix driver lacks
there, because felix_port_setup_tagger_data() just sets dp->priv up
unconditionally for the ocelot-8021q tagging protocol (luckily the
normal ocelot tagger doesn't need dp->priv).

In sja1105 the story is a bit longer, but I believe that can also be
cleaned up to stay within the confines of ->connect()/->disconnect().

So I guess we just need to be careful and push back against dubious use
during review.