net: sfp: fix state loss when updating state_hw_mask

Andrew reports that the SFF modules on one of the ZII platforms do not
indicate link up due to the SFP code believing that LOS indicating that
there is no signal being received from the remote end, but in fact the
LOS signal is showing that there is signal.

What makes SFF modules different from SFPs is they typically have an
inverted LOS, which uncovered this issue. When we read the hardware
state, we mask it with state_hw_mask so we ignore anything we're not
interested in. However, we don't re-read when state_hw_mask changes,
leading to sfp->state being stale.

Arrange for a software poll of the module state after we have parsed
the EEPROM in sfp_sm_mod_probe() and updated state_*_mask. This will
generate any necessary events for signal changes for the state
machine as well as updating sfp->state.
Reported-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Fixes: 8475c4b7 ("net: sfp: re-implement soft state polling setup")
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/sfp.c

@@ -2190,6 +2190,11 @@ static void sfp_sm_module(struct sfp *sfp, unsigned int event)
 			break;
 		}
 
+		/* Force a poll to re-read the hardware signal state after
+		 * sfp_sm_mod_probe() changed state_hw_mask.
+		 */
+		mod_delayed_work(system_wq, &sfp->poll, 1);
+
 		err = sfp_hwmon_insert(sfp);
 		if (err)
 			dev_warn(sfp->dev, "hwmon probe failed: %pe\n",