[PATCH net v4] net: phy: qca83xx: read resolved QCA8337 link status

[Yongzhao Chen <yongzhao.derek@gmail.com>]

After a QCA8337 SmartSpeed downshift, genphy_read_status() can report
1000 Mbit/s from the advertised modes when the PHY is running at
100 Mbit/s. On a Redmi AX5400 running downstream OpenWrt Linux 6.18.52,
this caused qca8k to program the user-port MAC for 1000 Mbit/s and
traffic failed. An earlier prototype that read the resolved speed
from the PHY restored traffic.

Wrap genphy_read_status() and use at803x_read_specific_status() to
replace its speed and duplex result when an autonegotiated link comes
up. Resolve pause for the resulting duplex. Until the PHY reports a
resolved speed and duplex, report the link as down so that the next
poll reads them again, as marvell_read_status_page_an() does.
QCA8337's register layout matches the helper (data sheet 80-Y0619-3
Rev. D, pages 327-328).

Keep the generic master/slave read order and the early return for a
steady autonegotiated link. This avoids additional reads of the
clear-on-read idle error count in MII_STAT1000. Forced mode continues
to use BMCR. Report the MDI-X state read at link-up and invalidate it
when the link goes down or autonegotiation is disabled. Clear
mdix_ctrl because this driver does not implement MDI-X configuration.

Fixes: b3591c2a3661 ("net: dsa: qca8k: Switch to PHYLINK instead of PHYLIB")
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Yongzhao Chen <yongzhao.derek@gmail.com>
Assisted-by: LLM
---
v4:
 - Report the link as down while the PHY-specific status is unresolved
   or holds the reserved speed value, as marvell_read_status_page_an()
   does. v3 reported the link up with SPEED_UNKNOWN, and the early
   return then kept it until the link dropped.
 - Invalidate mdix when the link goes down or autonegotiation is
   disabled, instead of keeping the value read at the last link-up.
 - Rebased onto net 37f12441f557. The files involved are unchanged.
 Both issues were raised in the Sashiko review of v3, which Jakub
 forwarded.

v3: https://lore.kernel.org/netdev/20261006160316.1356-1-yongzhao.derek@gmail.com/
v2: https://lore.kernel.org/netdev/20261003173210.1235-1-yongzhao.derek@gmail.com/
v1: https://lore.kernel.org/netdev/20260928220749.857-1-yongzhao.derek@gmail.com/

Testing: the source-extraction model passes 27 checks covering speed
and duplex at the phylib notification boundary, latch-low transitions,
pause, forced mode, MDIO errors, the idle-error and MSFAIL read order
from v3, and the two issues above. v3 fails exactly the four checks
for those two issues: an unresolved or reserved status at link-up,
and mdix after a link drop or with autonegotiation disabled. An arm64
W=1 build of qca83xx.o, at803x.o and qcom-phy-lib.o is clean.

v4 has not been tested on hardware. The hardware result above used
v2's at803x_read_status() plus genphy_read_master_slave() on one board,
with an Intel igb peer, a two-pair cable and default autonegotiation.
Ping changed from 0/20 to 20/20 in each direction at resolved 100 Full.
Whether QCA8337 can report link up before the resolved bit is set is
unknown.

 drivers/net/phy/qcom/qca83xx.c | 53 ++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/net/phy/qcom/qca83xx.c b/drivers/net/phy/qcom/qca83xx.c
index bc70ed8efd8..be00bc7cda0 100644
--- a/drivers/net/phy/qcom/qca83xx.c
+++ b/drivers/net/phy/qcom/qca83xx.c
@@ -92,6 +92,58 @@ static int qca83xx_probe(struct phy_device *phydev)
 	return 0;
 }
 
+static int qca8337_read_status(struct phy_device *phydev)
+{
+	struct at803x_ss_mask ss_mask = {
+		.speed_mask = AT803X_SS_SPEED_MASK,
+		.speed_shift = __bf_shf(AT803X_SS_SPEED_MASK),
+	};
+	int ret, old_link = phydev->link;
+
+	ret = genphy_read_status(phydev);
+	if (ret)
+		return ret;
+
+	/* Keep the state resolved at link-up while the link stays up */
+	if (phydev->autoneg == AUTONEG_ENABLE && old_link && phydev->link)
+		goto out;
+
+	phydev->mdix = ETH_TP_MDI_INVALID;
+
+	/* genphy_read_status() derives speed and duplex from the
+	 * advertisements, which is wrong after a SmartSpeed downshift.
+	 * Use what the PHY resolved instead.
+	 */
+	if (phydev->autoneg == AUTONEG_ENABLE && phydev->autoneg_complete &&
+	    phydev->link) {
+		phydev->speed = SPEED_UNKNOWN;
+		phydev->duplex = DUPLEX_UNKNOWN;
+		phydev->pause = false;
+		phydev->asym_pause = false;
+
+		ret = at803x_read_specific_status(phydev, ss_mask);
+		if (ret)
+			return ret;
+
+		/* Report the link down until speed and duplex are resolved,
+		 * so that the next poll reads them again.
+		 */
+		if (phydev->speed == SPEED_UNKNOWN ||
+		    phydev->duplex == DUPLEX_UNKNOWN) {
+			phydev->link = 0;
+			phydev->mdix = ETH_TP_MDI_INVALID;
+		} else {
+			phy_resolve_aneg_pause(phydev);
+		}
+	}
+
+out:
+	/* MDI-X configuration is not implemented */
+	phydev->mdix_ctrl = ETH_TP_MDI_INVALID;
+
+	return 0;
+}
+
 static int qca83xx_config_init(struct phy_device *phydev)
 {
 	u8 switch_revision;
@@ -220,6 +272,7 @@ static struct phy_driver qca83xx_driver[] = {
 	.flags			= PHY_IS_INTERNAL,
 	.config_init		= qca83xx_config_init,
 	.soft_reset		= genphy_soft_reset,
+	.read_status		= qca8337_read_status,
 	.get_sset_count		= qca83xx_get_sset_count,
 	.get_strings		= qca83xx_get_strings,
 	.get_stats		= qca83xx_get_stats,

base-commit: 37f12441f557468a56c1e27790413aa78c82afa2
-- 
2.43.0