The LAN7801 is designed exclusively for external PHYs (unlike the
LAN7800/LAN7850 which have internal PHYs), but lan78xx_mdio_init()
restricts PHY scanning to MDIO addresses 0-7 by setting phy_mask to
~(0xFF). This prevents discovery of external PHYs wired to addresses
outside that range.

One such case is the DP83TC814 100BASE-T1 PHY, which is typically
configured at MDIO address 10 via PHYAD bootstrap pins and goes
undetected with the current mask.

Set phy_mask to 0 for the LAN7801 so that all 32 MDIO addresses are
scanned during bus registration, allowing any external PHY to be
discovered regardless of its address.

Fixes: 02dc1f3d613d ("lan78xx: add LAN7801 MAC only support")

Signed-off-by: Martin Pålsson <redacted>
---
Changes in v2:
- Added Fixes: tag
- Link to v1: https://lore.kernel.org/r/20260214-lan78xx-phy-mask-fix-v1-1-3baa100861e4@poleshift.se
---
 drivers/net/usb/lan78xx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 00397a807393..9d8f1ff7028d 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c

@@ -2094,8 +2094,8 @@ static int lan78xx_mdio_init(struct lan78xx_net *dev)
 		dev->mdiobus->phy_mask = ~(1 << 1);
 		break;
 	case ID_REV_CHIP_ID_7801_:
-		/* scan thru PHYAD[2..0] */
-		dev->mdiobus->phy_mask = ~(0xFF);
+		/* scan all 32 MDIO addresses for external PHYs */
+		dev->mdiobus->phy_mask = 0;