[PATCH net] net: phy: fix phy_uses_state_machine()

["Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>]

phy_uses_state_machine() is called from the resume path (see
mdio_bus_phy_resume()) which will be called for all devices whether
they are connected to a network device or not.

phydev->phy_link_change is initialised by phy_attach_direct(), and
overridden by phylink. This means that a never-connected PHY will
have phydev->phy_link_change set to NULL, which causes
phy_uses_state_machine() to return true. This is incorrect.

Fix the case where phydev->phy_link_change is NULL.

Reported-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://lore.kernel.org/r/20250806082931.3289134-1-xu.yang_2@nxp.com
Fixes: fc75ea20ffb4 ("net: phy: allow MDIO bus PM ops to start/stop state machine for phylink-controlled PHY")
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
The provided Link: rather than Closes: is because there were two issues
identified in that thread, and this patch only addresses one of them.
Therefore, it is not correct to mark that issue closed.

Xu Yang reported this fixed the problem for him, and it is an oversight
in the phy_uses_state_machine() test.

 drivers/net/phy/phy_device.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 7556aa3dd7ee..e6a673faabe6 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -288,7 +288,7 @@ static bool phy_uses_state_machine(struct phy_device *phydev)
 		return phydev->attached_dev && phydev->adjust_link;
 
 	/* phydev->phy_link_change is implicitly phylink_phy_change() */
-	return true;
+	return !!phydev->phy_link_change;
 }
 
 static bool mdio_bus_phy_may_suspend(struct phy_device *phydev)
-- 
2.47.2