netdev - 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 13:54:31 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        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 04:32:43AM +0100, Ansuel Smith wrote:
> On Wed, Dec 08, 2021 at 03:09:47AM +0200, Vladimir Oltean wrote:
> > On Wed, Dec 08, 2021 at 01:42:59AM +0100, Ansuel Smith wrote:
> > > On Wed, Dec 08, 2021 at 02:40:51AM +0200, Vladimir Oltean wrote:
> > > > On Wed, Dec 08, 2021 at 02:04:32AM +0200, Vladimir Oltean wrote:
> > > > > 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.
> > > > 
> > > > I've started working on a prototype for converting sja1105 to this model.
> > > > It should be clearer to me by tomorrow whether there is anything missing
> > > > from this proposal.
> > > 
> > > I'm working on your suggestion and I should be able to post another RFC
> > > this night if all works correctly with my switch.
> > 
> > Ok. The key point with my progress so far is that Andrew may be right
> > and we might need separate tagger priv pointers per port and per switch.
> > At least for the cleanliness of implementation. In the end I plan to
> > remove dp->priv and stay with dp->tagger_priv and ds->tagger_priv.
> > 
> > Here's what I have so far. I have more changes locally, but the rest it
> > isn't ready and overall also a bit irrelevant for the discussion.
> > I'm going to sleep now.
> >
> 
> BTW, I notice we made the same mistake. Don't know if it was the problem
> and you didn't notice... The notifier is not ready at times of the first
> tagger setup and the tag_proto_connect is never called.
> Anyway sending v2 with your suggestion applied.

I didn't go past the compilation stage yesterday. Anyway, now that you
mention it, I remember Tobias hitting this issue as well when he worked
on changing tagging protocol via device tree, and this is why
dsa_switch_setup_tag_protocol() exists.  I believe that's where we'd
need to call ds->ops->connect_tag_proto from, like this:

static int dsa_switch_setup_tag_protocol(struct dsa_switch *ds)
{
	const struct dsa_device_ops *tag_ops = ds->dst->tag_ops;
	struct dsa_switch_tree *dst = ds->dst;
	struct dsa_port *cpu_dp;
	int err;

	if (tag_ops->proto == dst->default_proto)
		goto connect;

	dsa_switch_for_each_cpu_port(cpu_dp, ds) {
		rtnl_lock();
		err = ds->ops->change_tag_protocol(ds, cpu_dp->index,
						   tag_ops->proto);
		rtnl_unlock();
		if (err) {
			dev_err(ds->dev, "Unable to use tag protocol \"%s\": %pe\n",
				tag_ops->name, ERR_PTR(err));
			return err;
		}
	}

connect:
	if (ds->ops->connect_tag_protocol) {
		err = ds->ops->connect_tag_protocol(ds, tag_ops->proto);
		if (err) {
			dev_err(ds->dev,
				"Unable to connect to tag protocol \"%s\": %pe\n",
				tag_ops->name, ERR_PTR(err));
			return err;
		}
	}

	return 0;
}