[PATCH net v2 2/2] net: ethernet: mtk_eth_soc: populate lpi_interfaces to fix EEE support

[Aleksei Sviridkin <f@lex.la>]

mtk_add_mac() fills in lpi_capabilities and lpi_timer_default but
never lpi_interfaces, so phylink treats every MAC that uses
mtk_phylink_ops as not supporting EEE: ethtool reports "Not
supported" and phy_disable_eee() keeps userspace locked out. MT7628
is unaffected, as rt5350_phylink_ops has no tx_lpi methods.

Copy the supported interfaces into lpi_interfaces once the SoC
specific fixups have finished changing them, and leave 2.5 Gbps out
for now: drop 2500BASE-X from the copy and MAC_2500FD from
lpi_capabilities. MAC_MCR folds SPEED_2500 onto MAC_MCR_SPEED_1000, so
MAC_MCR_EEE1G is what would govern LPI on such a link, and it is
unvalidated rather than unsupported: MediaTek's SDK driver sets the
EEE force bits for 100 Mbps and 1 Gbps link speed only, EEE signalling
on 2500BASE-X is outside 802.3, and the 1 us unit of the wakeup timers
is undocumented with the port clock at 2.5 times the rate. Narrowing
lpi_capabilities alone would not do it, since it gates on the media
speed a rate matching PHY reports rather than on the speed the MAC
runs at. Drop the xGMII modes too, which mtk_mac_enable_tx_lpi()
refuses outright and which on netsys v3 include the mode of MT7988's
built-in 2.5G PHY.

LPI stays off until userspace enables it. The EEE advertisement of a
PHY that advertises it out of reset does come back, since phylink
stops force-clearing it.

Fixes: 952d7325362f ("net: ethernet: mediatek: add EEE support")
Signed-off-by: Aleksei Sviridkin <f@lex.la>
---

On leaving 2.5 Gbps out: the absence of 2.5 Gbps EEE force bits in
MAC_MCR is not the argument, since the same reasoning applied to the
speed field would say the MAC cannot do 2.5 Gbps at all - 2500BASE-X
here is 1000BASE-X at 2.5 times the clock, and the MAC does not know
the difference. MAC_2500FD was deliberate in the original EEE
submission [1], which set MAC_MCR_EEE1G for SPEED_2500 and SPEED_1000
alike. The masks say nobody has validated it, not that the hardware
refuses.

On the netsys v3 switch MAC the xGMII filter empties lpi_interfaces
outright, as PHY_INTERFACE_MODE_INTERNAL is the only interface it
supports. It is a fixed link port with no PHY, so phylink had no EEE to
manage there before this patch either.

Pre-existing, made live by this patch and not addressed here:
mtk_mac_enable_tx_lpi() programs MT7531's reset wakeup times (17 for
1 Gbps, 36 for 100 Mbps) whenever it runs, as its own comment says, so
they now apply to every SoC driven by mtk_phylink_ops once a user
enables EEE on an eligible interface. Those values do not appear to
have been confirmed for MT7981, MT7986 or MT7988.

[1] https://lore.kernel.org/all/20250210125246.1950142-1-dqfext@gmail.com/
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 22 ++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index be3bd025c41a..37a831f73da6 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -4828,7 +4828,7 @@ static int mtk_add_mac(struct mtk_eth *eth, struct device_node *np)
 	phy_interface_t phy_mode;
 	struct phylink *phylink;
 	struct mtk_mac *mac;
-	int id, err;
+	int id, err, i;
 	int txqs = 1;
 	u32 val;
 
@@ -4907,8 +4907,11 @@ static int mtk_add_mac(struct mtk_eth *eth, struct device_node *np)
 	mac->phylink_config.type = PHYLINK_NETDEV;
 	mac->phylink_config.mac_capabilities = MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
 		MAC_10 | MAC_100 | MAC_1000 | MAC_2500FD;
-	mac->phylink_config.lpi_capabilities = MAC_100FD | MAC_1000FD |
-		MAC_2500FD;
+	/* MAC_MCR folds SPEED_2500 onto MAC_MCR_SPEED_1000, so LPI above
+	 * 1 Gbps would be governed by MAC_MCR_EEE1G and is unvalidated
+	 * rather than unsupported.
+	 */
+	mac->phylink_config.lpi_capabilities = MAC_100FD | MAC_1000FD;
 	mac->phylink_config.lpi_timer_default = 1000;
 
 	/* MT7623 gmac0 is now missing its speed-specific PLL configuration
@@ -4966,6 +4969,19 @@ static int mtk_add_mac(struct mtk_eth *eth, struct device_node *np)
 		__set_bit(PHY_INTERFACE_MODE_INTERNAL,
 			  mac->phylink_config.supported_interfaces);
 
+	phy_interface_copy(mac->phylink_config.lpi_interfaces,
+			   mac->phylink_config.supported_interfaces);
+
+	/* The MAC side of 2500BASE-X is never below 2.5 Gbps, not even when
+	 * a rate matching PHY drops the media to 1 Gbps, and
+	 * mtk_mac_enable_tx_lpi() refuses the xGMII modes outright.
+	 */
+	__clear_bit(PHY_INTERFACE_MODE_2500BASEX,
+		    mac->phylink_config.lpi_interfaces);
+	for (i = 0; i < PHY_INTERFACE_MODE_MAX; i++)
+		if (mtk_interface_mode_is_xgmii(eth, i))
+			__clear_bit(i, mac->phylink_config.lpi_interfaces);
+
 	phylink = phylink_create(&mac->phylink_config,
 				 of_fwnode_handle(mac->of_node),
 				 phy_mode, mac_ops);
-- 
2.55.0