[PATCH net-next] net: phylink: avoid oops during initialisation

[Russell King <rmk+kernel@armlinux.org.uk>]

If we intend to use PCS operations, mac_pcs_get_state() will not be
implemented, so will be NULL. If we also intend to register the PCS
operations in mac_prepare() or mac_config(), then this leads to an
attempt to call NULL function pointer during phylink_start(). Avoid
this, but we must report the link is down.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
There are no users of the new split PCS support currently, so this
does not require backporting, but if people think it should have a
fixes tag, that would be:
     Fixes: 7137e18f6f88 ("net: phylink: add struct phylink_pcs")

 drivers/net/phy/phylink.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 32b4bd6a5b55..5e4cb12972eb 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -535,8 +535,10 @@ static void phylink_mac_pcs_get_state(struct phylink *pl,
 
 	if (pl->pcs_ops)
 		pl->pcs_ops->pcs_get_state(pl->pcs, state);
-	else
+	else if (pl->mac_ops->mac_pcs_get_state)
 		pl->mac_ops->mac_pcs_get_state(pl->config, state);
+	else
+		state->link = 0;
 }
 
 /* The fixed state is... fixed except for the link state,
-- 
2.20.1