The Lynx PCS USXGMII setup programs the replicator advertisement, but
does not explicitly enable and restart in-band autonegotiation or program
the replicator link timers.

This leaves the PCS dependent on firmware or bootloader state. Systems
which do not get the USXGMII replicator preconfigured before Linux may
therefore fail to negotiate the link correctly.

After programming the USXGMII device ability, configure the replicator
BMCR with reset, autonegotiation enable and autonegotiation restart. Also
program the replicator link timer registers with the values used by the
ENETC/Felix setup.

Signed-off-by: Patryk Biel <pbiel7@gmail.com>
---
This is a follow-up to the discussion started here:

Link: https://lore.kernel.org/netdev/CA+DkFDaW_wJ5p9_P7pMpz-8iE6xeKkdF-MQcd2m2GcyVUE3S4Q@mail.gmail.com/

To summarize: on systems that don't rely on the U-Boot Felix switch
driver to pre-configure 10G-QXGMII in-band autonegotiation, the Lynx
PCS USXGMII code programs the replicator device ability but never
actually enables/restarts autonegotiation nor sets up the replicator
link timers. This leaves link establishment dependent on bootloader
state that isn't guaranteed to exist.

This series only addresses the PCS side of the problem: it configures
the USXGMII replicator BMCR (reset/AN enable/AN restart) and the link
timer registers whenever lynx_pcs_config_usxgmii() is called, so that
in-band AN comes up correctly regardless of what the bootloader did.

It intentionally does NOT yet remove the "only supports in-band AN for
now" limitation, nor does it wire up neg_mode-based configuration to
support the managed = "in-band-status" property being absent from the
device tree. That part still needs more work/testing on my side (in
particular the in-band-disable path isn't behaving as expected yet
with the PHY I'm testing against), and I'd like to discuss the right
approach for it separately before sending a follow-up series.

Feedback welcome, especially on whether this is an acceptable
incremental step or whether it should be bundled together with the
neg_mode/in-band-disable work
---
Changes in v2:
- Reorder local variable declarations in lynx_pcs_config_usxgmii().
- Move USXGMII replicator link timer configuration before the autonegotiation restart.
- Use phylink_get_link_timer_ns() instead of hardcoded USXGMII 
  replicator link timer values, converting to 3.2 ns register step.
- Link to v1: https://lore.kernel.org/r/20260820-b4-fix-pcs-lynx-an-v1-1-62d66391eaff@gmail.com
---
 drivers/net/pcs/pcs-lynx.c | 47 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/drivers/net/pcs/pcs-lynx.c b/drivers/net/pcs/pcs-lynx.c
index a92081560e641ad2b297b7395cc72bf2f59ea16c..564c8a3d2b06fde92a249308f955566d6baac36f 100644
--- a/drivers/net/pcs/pcs-lynx.c
+++ b/drivers/net/pcs/pcs-lynx.c
@@ -20,6 +20,9 @@
 #define IF_MODE_SPEED_MSK		GENMASK(3, 2)
 #define IF_MODE_HALF_DUPLEX		BIT(4)
 
+/* USXGMII replicator link timer step is 3.2 ns (312.5 MHz clock) */
+#define USXGMII_LINK_TIMER_VAL(ns)	((u32)((ns) * 10 / 32))
+
 struct lynx_pcs {
 	struct phylink_pcs pcs;
 	struct mdio_device *mdio;
@@ -156,6 +159,9 @@ static int lynx_pcs_config_usxgmii(struct mdio_device *pcs,
 {
 	struct mii_bus *bus = pcs->bus;
 	int addr = pcs->addr;
+	int link_timer_ns;
+	u32 link_timer;
+	int ret;
 
 	if (neg_mode != PHYLINK_PCS_NEG_INBAND_ENABLED) {
 		dev_err(&pcs->dev, "%s only supports in-band AN for now\n",
@@ -164,10 +170,43 @@ static int lynx_pcs_config_usxgmii(struct mdio_device *pcs,
 	}
 
 	/* Configure device ability for the USXGMII Replicator */
-	return mdiobus_c45_write(bus, addr, MDIO_MMD_VEND2, MII_ADVERTISE,
-				 MDIO_USXGMII_10G | MDIO_USXGMII_LINK |
-				 MDIO_USXGMII_FULL_DUPLEX |
-				 ADVERTISE_SGMII | ADVERTISE_LPACK);
+	ret = mdiobus_c45_write(bus, addr, MDIO_MMD_VEND2, MII_ADVERTISE,
+				MDIO_USXGMII_10G | MDIO_USXGMII_LINK |
+				MDIO_USXGMII_FULL_DUPLEX |
+				ADVERTISE_SGMII | ADVERTISE_LPACK);
+	if (ret < 0) {
+		dev_err(&pcs->dev, "could not set USXGMII replicator config\n");
+		return ret;
+	}
+
+	link_timer_ns = phylink_get_link_timer_ns(interface);
+	if (link_timer_ns > 0) {
+		link_timer = USXGMII_LINK_TIMER_VAL(link_timer_ns);
+
+		ret = mdiobus_c45_write(bus, addr, MDIO_MMD_VEND2,
+					LINK_TIMER_LO, link_timer & 0xffff);
+		if (ret < 0) {
+			dev_err(&pcs->dev, "could not set USXGMII Link Timer 1\n");
+			return ret;
+		}
+
+		ret = mdiobus_c45_write(bus, addr, MDIO_MMD_VEND2,
+					LINK_TIMER_HI, (link_timer >> 16) & 0x1f);
+		if (ret < 0) {
+			dev_err(&pcs->dev, "could not set USXGMII Link Timer 2\n");
+			return ret;
+		}
+	}
+
+	/* Configure autonegotiation */
+	ret = mdiobus_c45_write(bus, addr, MDIO_MMD_VEND2, MII_BMCR,
+				BMCR_RESET | BMCR_ANENABLE | BMCR_ANRESTART);
+	if (ret < 0) {
+		dev_err(&pcs->dev, "could not set USXGMII replicator control config\n");
+		return ret;
+	}
+
+	return ret;
 }
 
 static int lynx_pcs_config(struct phylink_pcs *pcs, unsigned int neg_mode,

---
base-commit: 7cbfb180945ce529608e4d4e24a6d483699fab1e
change-id: 20260820-b4-fix-pcs-lynx-an-3fd1d5e94ce6

Best regards,
-- 
Patryk Biel <pbiel7@gmail.com>