[PATCH net] dpll: fix build failure due to rcu_dereference_check() on unknown type

[Jakub Kicinski <kuba@kernel.org>]

From: Eric Dumazet <edumazet@google.com>

Tasmiya reports that their compiler complains that we deref
a pointer to unknown type with rcu_dereference_rtnl():

include/linux/rcupdate.h:439:9: error: dereferencing pointer to incomplete type ‘struct dpll_pin’

Unclear what compiler it is, at the moment, and we can't report
but since DPLL can't be a module - move the code from the header
into the source file.

Fixes: 0d60d8df6f49 ("dpll: rely on rcu for netdev_dpll_pin()")
Reported-by: Tasmiya Nalatwad <tasmiya@linux.vnet.ibm.com>
Link: https://lore.kernel.org/all/3fcf3a2c-1c1b-42c1-bacb-78fdcd700389@linux.vnet.ibm.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
Sending officially the solution Eric suggested in the report
thread. The bug is pending in the net tree, so I'd like to
put this on an express path, to make today's PR...

CC: vadim.fedorenko@linux.dev
CC: arkadiusz.kubalewski@intel.com
CC: jiri@resnulli.us
---
 drivers/dpll/dpll_core.c | 5 +++++
 include/linux/dpll.h     | 8 ++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/dpll/dpll_core.c b/drivers/dpll/dpll_core.c
index 4c2bb27c99fe..507dd9cfb075 100644
--- a/drivers/dpll/dpll_core.c
+++ b/drivers/dpll/dpll_core.c
@@ -42,6 +42,11 @@ struct dpll_pin_registration {
 	void *priv;
 };
 
+struct dpll_pin *netdev_dpll_pin(const struct net_device *dev)
+{
+       return rcu_dereference_rtnl(dev->dpll_pin);
+}
+
 struct dpll_device *dpll_device_get_by_id(int id)
 {
 	if (xa_get_mark(&dpll_device_xa, id, DPLL_REGISTERED))
diff --git a/include/linux/dpll.h b/include/linux/dpll.h
index 4ec2fe9caf5a..c60591308ae8 100644
--- a/include/linux/dpll.h
+++ b/include/linux/dpll.h
@@ -169,13 +169,13 @@ int dpll_device_change_ntf(struct dpll_device *dpll);
 
 int dpll_pin_change_ntf(struct dpll_pin *pin);
 
+#if !IS_ENABLED(CONFIG_DPLL)
 static inline struct dpll_pin *netdev_dpll_pin(const struct net_device *dev)
 {
-#if IS_ENABLED(CONFIG_DPLL)
-	return rcu_dereference_rtnl(dev->dpll_pin);
-#else
 	return NULL;
-#endif
 }
+#else
+struct dpll_pin *netdev_dpll_pin(const struct net_device *dev);
+#endif
 
 #endif
-- 
2.43.2