From: Vladimir Oltean vladimir.oltean@nxp.com
[ Upstream commit a2c65a9d0568b6737c02b54f00b80716a53fac61 ]
DSA tagging protocol drivers can be changed at runtime through sysfs and at probe time through the device tree (support for the latter was added later).
When changing through sysfs, it is assumed that the module for the new tagging protocol was already loaded into the kernel (in fact this is only a concern for Ocelot/Felix switches, where we have tag_ocelot.ko and tag_ocelot_8021q.ko; for every other switch, the default and alternative protocols are compiled within the same .ko, so there is nothing for the user to load).
The kernel cannot currently call request_module(), because it has no way of constructing the modalias name of the tagging protocol driver ("dsa_tag-%d", where the number is one of DSA_TAG_PROTO_*_VALUE). The device tree only contains the string name of the tagging protocol ("ocelot-8021q"), and the only mapping between the string and the DSA_TAG_PROTO_OCELOT_8021Q_VALUE is present in tag_ocelot_8021q.ko. So this is a chicken-and-egg situation and dsa_core.ko has nothing based on which it can automatically request the insertion of the module.
As a consequence, if CONFIG_NET_DSA_TAG_OCELOT_8021Q is built as module, the switch will forever defer probing.
The long-term solution is to make DSA call request_module() somehow, but that probably needs some refactoring.
What we can do to keep operating with existing device tree blobs is to cancel the attempt to change the tagging protocol with the one specified there, and to remain operating with the default one. Depending on the situation, the default protocol might still allow some functionality (in the case of ocelot, it does), and it's better to have that than to fail to probe.
Fixes: deff710703d8 ("net: dsa: Allow default tag protocol to be overridden from DT") Link: https://lore.kernel.org/lkml/20221027113248.420216-1-michael@walle.cc/ Reported-by: Heiko Thiery heiko.thiery@gmail.com Reported-by: Michael Walle michael@walle.cc Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Tested-by: Michael Walle michael@walle.cc Reviewed-by: Florian Fainelli f.fainelli@gmail.com Link: https://lore.kernel.org/r/20221027145439.3086017-1-vladimir.oltean@nxp.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/dsa/dsa2.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c index cac48a741f27..e537655e442b 100644 --- a/net/dsa/dsa2.c +++ b/net/dsa/dsa2.c @@ -1407,9 +1407,9 @@ static enum dsa_tag_protocol dsa_get_tag_protocol(struct dsa_port *dp, static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master, const char *user_protocol) { + const struct dsa_device_ops *tag_ops = NULL; struct dsa_switch *ds = dp->ds; struct dsa_switch_tree *dst = ds->dst; - const struct dsa_device_ops *tag_ops; enum dsa_tag_protocol default_proto;
/* Find out which protocol the switch would prefer. */ @@ -1432,10 +1432,17 @@ static int dsa_port_parse_cpu(struct dsa_port *dp, struct net_device *master, }
tag_ops = dsa_find_tagger_by_name(user_protocol); - } else { - tag_ops = dsa_tag_driver_get(default_proto); + if (IS_ERR(tag_ops)) { + dev_warn(ds->dev, + "Failed to find a tagging driver for protocol %s, using default\n", + user_protocol); + tag_ops = NULL; + } }
+ if (!tag_ops) + tag_ops = dsa_tag_driver_get(default_proto); + if (IS_ERR(tag_ops)) { if (PTR_ERR(tag_ops) == -ENOPROTOOPT) return -EPROBE_DEFER;