net: phy: Add phydev->enable_tx_lpi to simplify adjust link callbacks

MAC drivers which support EEE need to know the results of the EEE
auto-neg in order to program the hardware to perform EEE or not.  The
oddly named phy_init_eee() can be used to determine this, it returns 0
if EEE should be used, or a negative error code,
e.g. -EOPPROTONOTSUPPORT if the PHY does not support EEE or negotiate
resulted in it not being used.

However, many MAC drivers get this wrong. Add phydev->enable_tx_lpi
which indicates the result of the autoneg for EEE, including if EEE is
administratively disabled with ethtool. The MAC driver can then access
this in the same way as link speed and duplex in the adjust link
callback. If enable_tx_lpi is true, the MAC should send low power
indications and does not need to consider anything else with respect
to EEE.

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20240302195306.3207716-3-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phy.c

@@ -983,9 +983,16 @@ static int phy_check_link_status(struct phy_device *phydev)
 	if (phydev->link && phydev->state != PHY_RUNNING) {
 		phy_check_downshift(phydev);
 		phydev->state = PHY_RUNNING;
+		err = genphy_c45_eee_is_active(phydev,
+					       NULL, NULL, NULL);
+		if (err < 0)
+			phydev->enable_tx_lpi = false;
+		else
+			phydev->enable_tx_lpi = !!err;
 		phy_link_up(phydev);
 	} else if (!phydev->link && phydev->state != PHY_NOLINK) {
 		phydev->state = PHY_NOLINK;
+		phydev->enable_tx_lpi = false;
 		phy_link_down(phydev);
 	}
 

include/linux/phy.h

@@ -594,6 +594,7 @@ struct macsec_ops;
  * @supported_eee: supported PHY EEE linkmodes
  * @advertising_eee: Currently advertised EEE linkmodes
  * @eee_enabled: Flag indicating whether the EEE feature is enabled
+ * @enable_tx_lpi: When True, MAC should transmit LPI to PHY
  * @lp_advertising: Current link partner advertised linkmodes
  * @host_interfaces: PHY interface modes supported by host
  * @eee_broken_modes: Energy efficient ethernet modes which should be prohibited
@@ -713,6 +714,7 @@ struct phy_device {
 
 	/* Energy efficient ethernet modes which should be prohibited */
 	u32 eee_broken_modes;
+	bool enable_tx_lpi;
 
 #ifdef CONFIG_LED_TRIGGER_PHY
 	struct phy_led_trigger *phy_led_triggers;