The TI DP83826 PHY can operate in either MII mode or RMII mode.
By default, it is configured by straps.
It can also be configured by writing to the bit 5 of register 0x17 - RMII
and Status Register (RCSR).

When phydev->interface is rmii, rmii mode must be enabled, otherwise
mii mode must be set.
This prevents misconfiguration of hw straps.

Signed-off-by: Jérémie Dautheribes <redacted>
---
 drivers/net/phy/dp83822.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/phy/dp83822.c b/drivers/net/phy/dp83822.c
index 30f2616ab1c2..2d8275e59dcc 100644
--- a/drivers/net/phy/dp83822.c
+++ b/drivers/net/phy/dp83822.c

@@ -100,6 +100,7 @@
 #define DP83822_WOL_CLR_INDICATION BIT(11)
 
 /* RCSR bits */
+#define DP83822_RMII_MODE_EN	BIT(5)
 #define DP83822_RGMII_MODE_EN	BIT(9)
 #define DP83822_RX_CLK_SHIFT	BIT(12)
 #define DP83822_TX_CLK_SHIFT	BIT(11)

@@ -500,6 +501,16 @@ static int dp83826_config_init(struct phy_device *phydev)
 	u16 val, mask;
 	int ret;
 
+	if (phydev->interface == PHY_INTERFACE_MODE_RMII)
+		ret = phy_set_bits_mmd(phydev, DP83822_DEVADDR, MII_DP83822_RCSR,
+				       DP83822_RMII_MODE_EN);
+	else
+		ret = phy_clear_bits_mmd(phydev, DP83822_DEVADDR, MII_DP83822_RCSR,
+					 DP83822_RMII_MODE_EN);