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net: phy: smsc: Force predictable MDI-X state on LAN87xx

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Override the hardware strap configuration for MDI-X mode to ensure a
predictable initial state for the driver. The initial mode of the LAN87xx
PHY is determined by the AUTOMDIX_EN strap pin, but the driver has no
documented way to read its latched status.

This unpredictability means the driver cannot know if the PHY has
initialized with Auto-MDIX enabled or disabled, preventing it from
providing a reliable interface to the user.

This patch introduces a `config_init` hook that forces the PHY into a
known state by explicitly enabling Auto-MDIX.

Fixes: 05b35e7eb9 ("smsc95xx: add phylib support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Andre Edich <andre.edich@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250703114941.3243890-3-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Oleksij Rempel
2025-07-03 13:49:40 +02:00
committed by Jakub Kicinski
parent a141af8eb2
commit 0713e55533
1 changed files with 28 additions and 1 deletions
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29
drivers/net/phy/smsc.c
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@@ -262,6 +262,33 @@ int lan87xx_read_status(struct phy_device *phydev)
}
EXPORT_SYMBOL_GPL(lan87xx_read_status);
static int lan87xx_phy_config_init(struct phy_device *phydev)
{
int rc;
/* The LAN87xx PHY's initial MDI-X mode is determined by the AUTOMDIX_EN
* hardware strap, but the driver cannot read the strap's status. This
* creates an unpredictable initial state.
*
* To ensure consistent and reliable behavior across all boards,
* override the strap configuration on initialization and force the PHY
* into a known state with Auto-MDIX enabled, which is the expected
* default for modern hardware.
*/
rc = phy_modify(phydev, SPECIAL_CTRL_STS,
SPECIAL_CTRL_STS_OVRRD_AMDIX_ |
SPECIAL_CTRL_STS_AMDIX_ENABLE_ |
SPECIAL_CTRL_STS_AMDIX_STATE_,
SPECIAL_CTRL_STS_OVRRD_AMDIX_ |
SPECIAL_CTRL_STS_AMDIX_ENABLE_);
if (rc < 0)
return rc;
phydev->mdix_ctrl = ETH_TP_MDI_AUTO;
return smsc_phy_config_init(phydev);
}
static int lan874x_phy_config_init(struct phy_device *phydev)
{
u16 val;
@@ -696,7 +723,7 @@ static struct phy_driver smsc_phy_driver[] = {
/* basic functions */
.read_status = lan87xx_read_status,
.config_init = smsc_phy_config_init,
.config_init = lan87xx_phy_config_init,
.soft_reset = smsc_phy_reset,
.config_aneg = lan87xx_config_aneg,