Re: [PATCH net] net: phy: dp83869: Set auto mdix bit for forced 100Base-Tx mode
From: Meghana Malladi
Date: Wed Feb 11 2026 - 09:10:14 EST
Hi Andrew,
On 2/11/26 19:34, Andrew Lunn wrote:
On Wed, Feb 11, 2026 at 07:23:12PM +0530, Meghana Malladi wrote:
Hi Russell,
On 2/11/26 18:56, Russell King (Oracle) wrote:
On Wed, Feb 11, 2026 at 06:40:32PM +0530, Meghana Malladi wrote:
When using DP83869 in force 100Base-Tx mode, the PHY is required
to have robust Auto-MDIX feature enabled from register 1Eh.
Refer to 7.4.1.2 100BASE-TX section in the TRM [1] for more details.
[1]: https://www.ti.com/lit/ds/symlink/dp83869hm.pdf
Signed-off-by: Meghana Malladi <m-malladi@xxxxxx>
---
drivers/net/phy/dp83869.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/drivers/net/phy/dp83869.c b/drivers/net/phy/dp83869.c
index 1f381d7b13ff..70d759c45c6a 100644
--- a/drivers/net/phy/dp83869.c
+++ b/drivers/net/phy/dp83869.c
@@ -110,6 +110,7 @@
/* CFG4 bits */
#define DP83869_INT_OE BIT(7)
+#define DP83869_CFG4_ENABLE_AUTO_MDIX_100FD BIT(9)
/* OP MODE */
#define DP83869_OP_MODE_MII BIT(5)
@@ -900,6 +901,23 @@ static int dp83869_phy_reset(struct phy_device *phydev)
return dp83869_config_init(phydev);
}
+static void dp83869_link_change_notify(struct phy_device *phydev)
+{
+ int cfg4;
+
+ /* When using DP83869 in force 100Base-Tx mode, the PHY is required
+ * to have robust Auto-MDIX feature enabled
+ */
+ if (phydev->autoneg == AUTONEG_DISABLE &&
+ phydev->speed == SPEED_100 &&
+ phydev->duplex == DUPLEX_FULL) {
+ cfg4 = phy_read(phydev, DP83869_CFG4);
+ if (cfg4 >= 0) {
+ cfg4 |= DP83869_CFG4_ENABLE_AUTO_MDIX_100FD;
+ phy_write(phydev, DP83869_CFG4, cfg4);
+ }
+ }
Shouldn't this kind of configuration be done via .config_aneg() ?
AFAIK, in case of fixed mode, auto-neg might not be triggered all the time.
In the phy_ethtool_ksettings_set() function, auto-neg is initiated only if
the PHY hasn't started. PHY drivers are new to me, please do correct me if I
am wrong.
.config_aneg() is badly named, since it is also used for forced mode. Just check
phydev->autoneg == AUTONEG_DISABLE.
Ok thanks, will fix this in v2 then.
Andrew