As pointed out by Florian:
https://lore.kernel.org/linux-devicetree/b542b2e8-115c-4234-a464-e73aa6bece5c@broadcom.com/ (local)

The BCM6846 has a few extra registers and cannot reuse the
compatible string from other variants of the Unimac
MDIO block: we need to be able to tell them apart.

Signed-off-by: Linus Walleij <redacted>
---
Linus Walleij (2):
      dt-bindings: net: brcm,unimac-mdio: Add bcm6846-mdio
      net: phy: mdio-bcm-unimac: Add BCM6846 support

 Documentation/devicetree/bindings/net/brcm,unimac-mdio.yaml | 1 +
 drivers/net/mdio/mdio-bcm-unimac.c                          | 1 +
 2 files changed, 2 insertions(+)
---
base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
change-id: 20241012-bcm6846-mdio-116b12d4ed11

Best regards,
-- 
Linus Walleij [off-list ref]