net: sfp: Add tx-fault workaround for Huawei MA5671A SFP ONT

As noted elsewhere, various GPON SFP modules exhibit non-standard
TX-fault behaviour. In the tested case, the Huawei MA5671A, when used
in combination with a Marvell mv88e6085 switch, was found to
persistently assert TX-fault, resulting in the module being disabled.

This patch adds a quirk to ignore the SFP_F_TX_FAULT state, allowing the
module to function.

Change from v1: removal of erroneous return statment (Andrew Lunn)
Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220502223315.1973376-1-mnhagan88@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/sfp.c

@@ -250,6 +250,7 @@ struct sfp {
 	struct sfp_eeprom_id id;
 	unsigned int module_power_mW;
 	unsigned int module_t_start_up;
+	bool tx_fault_ignore;
 
 #if IS_ENABLED(CONFIG_HWMON)
 	struct sfp_diag diag;
@@ -1956,6 +1957,12 @@ static int sfp_sm_mod_probe(struct sfp *sfp, bool report)
 	else
 		sfp->module_t_start_up = T_START_UP;
 
+	if (!memcmp(id.base.vendor_name, "HUAWEI          ", 16) &&
+	    !memcmp(id.base.vendor_pn, "MA5671A         ", 16))
+		sfp->tx_fault_ignore = true;
+	else
+		sfp->tx_fault_ignore = false;
+
 	return 0;
 }
 
@@ -2409,7 +2416,10 @@ static void sfp_check_state(struct sfp *sfp)
 	mutex_lock(&sfp->st_mutex);
 	state = sfp_get_state(sfp);
 	changed = state ^ sfp->state;
-	changed &= SFP_F_PRESENT | SFP_F_LOS | SFP_F_TX_FAULT;
+	if (sfp->tx_fault_ignore)
+		changed &= SFP_F_PRESENT | SFP_F_LOS;
+	else
+		changed &= SFP_F_PRESENT | SFP_F_LOS | SFP_F_TX_FAULT;
 
 	for (i = 0; i < GPIO_MAX; i++)
 		if (changed & BIT(i))