I don't have documentation or hardware to test, but according to commit
99c864667c9f ("net: phy: aquantia: add support for AQCS109"), "From
software point of view, it should be almost equivalent to AQR107."

I am relatively confident that the GLOBAL_CFG registers read by
aqr_gen2_fill_interface_modes() are supported, because
aqr_gen2_read_status(), currently used by AQCS109, also reads them, and
I'm unaware of any reported problem.

The change is necessary because a future patch will introduce a
requirement for all aqr_gen2_read_status() callers to have previously
called aqr_gen2_read_global_syscfg(). This is done through
aqr_gen2_fill_interface_modes().

Cc: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/phy/aquantia/aquantia_main.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/aquantia/aquantia_main.c b/drivers/net/phy/aquantia/aquantia_main.c
index e3a18fc1b52a..a7b1862e8a26 100644
--- a/drivers/net/phy/aquantia/aquantia_main.c
+++ b/drivers/net/phy/aquantia/aquantia_main.c
@@ -899,7 +899,11 @@ static int aqcs109_config_init(struct phy_device *phydev)
 	if (!ret)
 		aqr107_chip_info(phydev);
 
-	return aqr107_set_downshift(phydev, MDIO_AN_VEND_PROV_DOWNSHIFT_DFLT);
+	ret = aqr107_set_downshift(phydev, MDIO_AN_VEND_PROV_DOWNSHIFT_DFLT);
+	if (ret)
+		return ret;
+
+	return aqr_gen2_fill_interface_modes(phydev);
 }
 
 static void aqr107_link_change_notify(struct phy_device *phydev)
-- 
2.34.1