netdev - [PATCH net-next] net: dsa: felix: Fix CPU port assignment when not last port

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Message-Id: <20191118181657.25333-1-olteanv@gmail.com>
Date:   Mon, 18 Nov 2019 20:16:57 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     davem@...emloft.net
Cc:     andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        claudiu.manoil@....com, alexandru.marginean@....com,
        xiaoliang.yang_1@....com, yangbo.lu@....com,
        netdev@...r.kernel.org, Vladimir Oltean <vladimir.oltean@....com>
Subject: [PATCH net-next] net: dsa: felix: Fix CPU port assignment when not last port

From: Vladimir Oltean <vladimir.oltean@....com>

On the NXP LS1028A, there are 2 Ethernet links between the Felix switch
and the ENETC:
- eno2 <-> swp4, at 2.5G
- eno3 <-> swp5, at 1G

Only one of the above Ethernet port pairs can act as a DSA link for
tagging.

When adding initial support for the driver, it was tested only on the 1G
eno3 <-> swp5 interface, due to the necessity of using PHYLIB initially
(which treats fixed-link interfaces as emulated C22 PHYs, so it doesn't
support fixed-link speeds higher than 1G).

After making PHYLINK work, it appears that swp4 still can't act as CPU
port. So it looks like ocelot_set_cpu_port was being called for swp4,
but then it was called again for swp5, overwriting the CPU port assigned
in the DT.

It appears that when you call dsa_upstream_port for a port that is not
defined in the device tree (such as swp5 when using swp4 as CPU port),
its dp->cpu_dp pointer is not initialized by dsa_tree_setup_default_cpu,
and this trips up the following condition in dsa_upstream_port:

	if (!cpu_dp)
		return port;

So the moral of the story is: don't call dsa_upstream_port for a port
that is not defined in the device tree, and therefore its dsa_port
structure is not completely initialized (ds->num_ports is still 6).

Fixes: 56051948773e ("net: dsa: ocelot: add driver for Felix switch family")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/dsa/ocelot/felix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
index d73c38c6cbcf..89d28f80b99d 100644
--- a/drivers/net/dsa/ocelot/felix.c
+++ b/drivers/net/dsa/ocelot/felix.c
@@ -314,7 +314,7 @@ static int felix_setup(struct dsa_switch *ds)
 	for (port = 0; port < ds->num_ports; port++) {
 		ocelot_init_port(ocelot, port);

-		if (port == dsa_upstream_port(ds, port))
+		if (dsa_is_cpu_port(ds, port))
 			ocelot_set_cpu_port(ocelot, port,
 					    OCELOT_TAG_PREFIX_NONE,
 					    OCELOT_TAG_PREFIX_LONG);
-- 
2.17.1