[PATCH net] net: dsa: Fix load order between DSA drivers and taggers

[Andrew Lunn <andrew@lunn.ch>]

The DSA core, DSA taggers and DSA drivers all make use of
module_init(). Hence they get initialised at device_initcall() time.
The ordering is non-deterministic. It can be a DSA driver is bound to
a device before the needed tag driver has been initialised, resulting
in the message:

No tagger for this switch

Rather than have this be fatal, return -EPROBE_DEFER so that it is
tried again later once all the needed drivers have been loaded.

Fixes: d3b8c04988ca ("dsa: Add boilerplate helper to register DSA tag driver modules")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---

I did wonder if we should play with the core and tag drivers and make
them use subsystem_initcall(), but EPROBE_DEFER seems to be the more
preferred solution nowadays.
---
 net/dsa/dsa2.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index 3abd173ebacb..96f787cf9b6e 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -623,6 +623,8 @@ static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master)
 	tag_protocol = ds->ops->get_tag_protocol(ds, dp->index);
 	tag_ops = dsa_tag_driver_get(tag_protocol);
 	if (IS_ERR(tag_ops)) {
+		if (PTR_ERR(tag_ops) == -ENOPROTOOPT)
+			return -EPROBE_DEFER;
 		dev_warn(ds->dev, "No tagger for this switch\n");
 		return PTR_ERR(tag_ops);
 	}
-- 
2.23.0