The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
  drivers/net/phy/phylink.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 1a7550f5fdf5..48f0b9b39491 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c

@@ -766,7 +766,7 @@ static void phylink_pcs_poll_stop(struct phylink *pl)
  
  static void phylink_pcs_poll_start(struct phylink *pl)
  {
-	if (pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
+	if (pl->pcs && pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
  		mod_timer(&pl->link_poll, jiffies + HZ);
  }