[PATCH net-next v2] net: macb: set default_an_inband to true for SGMII

[Charles Perry <charles.perry@microchip.com>]

Most platforms using GEM in SGMII mode use in-band autonegotiation
because it is on by default in GEM's 1G PCS and is always on since
commit e276e5e40e92 ("net: macb: Disable PCS auto-negotiation for SGMII
fixed-link mode"). Leave it on if possible using the "default_an_inband"
flag of "struct phylink_config" so that platforms that lack in-band
autonegotiation configurability at the PHY do not break with commit
1338cfef1ff1 ("net: macb: fix SGMII with inband aneg disabled") which
will turn off in-band autoneg for non hot pluggable PHYs.

Once the majority of the PHY drivers that support SGMII have the
->config_inband() callback, this commit could be reverted so that non
hot pluggable PHY use outband negotiation with macb, like its the case
for other MACs.

Fixes: 1338cfef1ff1 ("net: macb: fix SGMII with inband aneg disabled")
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Closes: https://lore.kernel.org/r/20260304-nebulizer-rounding-40fbc81a2ba1@spud
Signed-off-by: Charles Perry <charles.perry@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---

Notes:
    Changes in v2:
      - Add a missing Reported-by: and fix the Tested-by: tag (Conor)

 drivers/net/ethernet/cadence/macb_main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 963a5d4e1a88..d1fc6a9b9fe5 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -838,6 +838,12 @@ static int macb_mii_probe(struct net_device *dev)
 	if (bp->phy_interface == PHY_INTERFACE_MODE_SGMII) {
 		bp->phylink_config.poll_fixed_state = true;
 		bp->phylink_config.get_fixed_state = macb_get_pcs_fixed_state;
+		/* The PCSAUTONEG bit in PCSCNTRL is on out of reset. Setting
+		 * default_an_inband to true tells phylink to turn it off only
+		 * if necessary (e.g. a fixed link or a PHY that doesn't support
+		 * inband).
+		 */
+		bp->phylink_config.default_an_inband = true;
 	}
 
 	bp->phylink_config.mac_capabilities = MAC_ASYM_PAUSE |
-- 
2.47.3