netdev - Re: [PATCH net-next 0/4] net: dsa: b53: Clean up CPU/IMP ports

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Date:   Fri, 17 Sep 2021 14:21:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Rafał Miłecki <zajec5@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH net-next 0/4] net: dsa: b53: Clean up CPU/IMP ports

> > That DSA_PORT_TYPE_UNUSED would probably require investigating DSA & b53
> > behaviour *and* discussing it with DSA maintainer to make sure we don't
> > abuse that.
> 
> How absent are these ports in hardware? For DSA_PORT_TYPE_UNUSED we do
> register a devlink port, but if those ports are really not present in
> hardware, I'm thinking maybe the easiest way would be to supply a
> ds->disabled_port_mask before dsa_register_switch(), and DSA will simply
> skip those ports when allocating the dp, the devlink_port etc. So you
> will literally have nothing for them.

The basic idea seems O.K, we just need to be careful.

We have code like:

static inline bool dsa_is_dsa_port(struct dsa_switch *ds, int p)
{
	return dsa_to_port(ds, p)->type == DSA_PORT_TYPE_DSA;
}

static inline bool dsa_is_user_port(struct dsa_switch *ds, int p)
{
	return dsa_to_port(ds, p)->type == DSA_PORT_TYPE_USER;
}

dsa_to_port(ds, p) will return NULL, and then bad things will happen.

Maybe it would be safer to add DSA_PORT_TYPE_PHANTOM and do allocate
the dp?

    Andrew