[PATCH net v2 0/4] net: phy: smsc: robustness fixes for LAN87xx/LAN9500

[PATCH net v2 0/4] net: phy: smsc: robustness fixes for LAN87xx/LAN9500

[Oleksij Rempel]

changes v2:
- drop IRQ patch.
- no other changes are made

Hi all,

The SMSC 10/100 PHYs (LAN87xx family) found in smsc95xx (lan95xx)
USB-Ethernet adapters show several quirks around the Auto-MDIX feature:

- A hardware strap (AUTOMDIX_EN) may boot the PHY in fixed-MDI mode, and
  the current driver cannot always override it.

- When Auto-MDIX is left enabled while autonegotiation is forced off,
  the PHY endlessly swaps the TX/RX pairs and never links up.

- The driver sets the enable bit for Auto-MDIX but forgets the override
  bit, so userspace requests are silently ignored.

- Rapid configuration changes can wedge the link if PHY IRQs are
  enabled.

The four patches below make the MDIX state fully predictable and prevent
link failures in every tested strap / autoneg / MDI-X permutation.

Tested on LAN9512 Eval board.

Best Regards,
Oleksij

Oleksij Rempel (3):
  net: phy: smsc: Fix Auto-MDIX configuration when disabled by strap
  net: phy: smsc: Force predictable MDI-X state on LAN87xx
  net: phy: smsc: Fix link failure in forced mode with Auto-MDIX

 drivers/net/phy/smsc.c | 57 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 52 insertions(+), 5 deletions(-)

--
2.39.5

[PATCH net v2 1/3] net: phy: smsc: Fix Auto-MDIX configuration when disabled by strap

[Oleksij Rempel]

Correct the Auto-MDIX configuration to ensure userspace settings are
respected when the feature is disabled by the AUTOMDIX_EN hardware strap.

The LAN9500 PHY allows its default MDI-X mode to be configured via a
hardware strap. If this strap sets the default to "MDI-X off", the
driver was previously unable to enable Auto-MDIX from userspace.

When handling the ETH_TP_MDI_AUTO case, the driver would set the
SPECIAL_CTRL_STS_AMDIX_ENABLE_ bit but neglected to set the required
SPECIAL_CTRL_STS_OVRRD_AMDIX_ bit. Without the override flag, the PHY
falls back to its hardware strap default, ignoring the software request.

This patch corrects the behavior by also setting the override bit when
enabling Auto-MDIX. This ensures that the userspace configuration takes
precedence over the hardware strap, allowing Auto-MDIX to be enabled
correctly in all scenarios.

Fixes: 05b35e7eb9a1 ("smsc95xx: add phylib support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Andre Edich <andre.edich@microchip.com>
---
 drivers/net/phy/smsc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/smsc.c b/drivers/net/phy/smsc.c
index 31463b9e5697..adf12d7108b5 100644
--- a/drivers/net/phy/smsc.c
+++ b/drivers/net/phy/smsc.c
@@ -167,7 +167,8 @@ static int lan87xx_config_aneg(struct phy_device *phydev)
 			SPECIAL_CTRL_STS_AMDIX_STATE_;
 		break;
 	case ETH_TP_MDI_AUTO:
-		val = SPECIAL_CTRL_STS_AMDIX_ENABLE_;
+		val = SPECIAL_CTRL_STS_OVRRD_AMDIX_ |
+			SPECIAL_CTRL_STS_AMDIX_ENABLE_;
 		break;
 	default:
 		return genphy_config_aneg(phydev);
-- 
2.39.5

[PATCH net v2 2/3] net: phy: smsc: Force predictable MDI-X state on LAN87xx

[Oleksij Rempel]

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: 05b35e7eb9a1 ("smsc95xx: add phylib support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Andre Edich <andre.edich@microchip.com>
---
 drivers/net/phy/smsc.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/smsc.c b/drivers/net/phy/smsc.c
index adf12d7108b5..ad9a3d91bb8a 100644
--- a/drivers/net/phy/smsc.c
+++ b/drivers/net/phy/smsc.c
@@ -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,
 
-- 
2.39.5

[PATCH net v2 3/3] net: phy: smsc: Fix link failure in forced mode with Auto-MDIX

[Oleksij Rempel]

Force a fixed MDI-X mode when auto-negotiation is disabled to prevent
link instability.

When forcing the link speed and duplex on a LAN9500 PHY (e.g., with
`ethtool -s eth0 autoneg off ...`) while leaving MDI-X control in auto
mode, the PHY fails to establish a stable link. This occurs because the
PHY's Auto-MDIX algorithm is not designed to operate when
auto-negotiation is disabled. In this state, the PHY continuously
toggles the TX/RX signal pairs, which prevents the link partner from
synchronizing.

This patch resolves the issue by detecting when auto-negotiation is
disabled. If the MDI-X control mode is set to 'auto', the driver now
forces a specific, stable mode (ETH_TP_MDI) to prevent the pair
toggling. This choice of a fixed MDI mode mirrors the behavior the
hardware would exhibit if the AUTOMDIX_EN strap were configured for a
fixed MDI connection.

Fixes: 05b35e7eb9a1 ("smsc95xx: add phylib support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Andre Edich <andre.edich@microchip.com>
---
 drivers/net/phy/smsc.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/net/phy/smsc.c b/drivers/net/phy/smsc.c
index ad9a3d91bb8a..b6489da5cfcd 100644
--- a/drivers/net/phy/smsc.c
+++ b/drivers/net/phy/smsc.c
@@ -155,10 +155,29 @@ static int smsc_phy_reset(struct phy_device *phydev)
 
 static int lan87xx_config_aneg(struct phy_device *phydev)
 {
-	int rc;
+	u8 mdix_ctrl;
 	int val;
+	int rc;
+
+	/* When auto-negotiation is disabled (forced mode), the PHY's
+	 * Auto-MDIX will continue toggling the TX/RX pairs.
+	 *
+	 * To establish a stable link, we must select a fixed MDI mode.
+	 * If the user has not specified a fixed MDI mode (i.e., mdix_ctrl is
+	 * 'auto'), we default to ETH_TP_MDI. This choice of a ETH_TP_MDI mode
+	 * mirrors the behavior the hardware would exhibit if the AUTOMDIX_EN
+	 * strap were configured for a fixed MDI connection.
+	 */
+	if (phydev->autoneg == AUTONEG_DISABLE) {
+		if (phydev->mdix_ctrl == ETH_TP_MDI_AUTO)
+			mdix_ctrl = ETH_TP_MDI;
+		else
+			mdix_ctrl = phydev->mdix_ctrl;
+	} else {
+		mdix_ctrl = phydev->mdix_ctrl;
+	}
 
-	switch (phydev->mdix_ctrl) {
+	switch (mdix_ctrl) {
 	case ETH_TP_MDI:
 		val = SPECIAL_CTRL_STS_OVRRD_AMDIX_;
 		break;
@@ -184,7 +203,7 @@ static int lan87xx_config_aneg(struct phy_device *phydev)
 	rc |= val;
 	phy_write(phydev, SPECIAL_CTRL_STS, rc);
 
-	phydev->mdix = phydev->mdix_ctrl;
+	phydev->mdix = mdix_ctrl;
 	return genphy_config_aneg(phydev);
 }
 
-- 
2.39.5

Re: [PATCH net v2 1/3] net: phy: smsc: Fix Auto-MDIX configuration when disabled by strap

[Maxime Chevallier]

Hi Oleksij,

On Thu,  3 Jul 2025 13:49:39 +0200
Oleksij Rempel <o.rempel@pengutronix.de> wrote:

> Correct the Auto-MDIX configuration to ensure userspace settings are
> respected when the feature is disabled by the AUTOMDIX_EN hardware strap.
> 
> The LAN9500 PHY allows its default MDI-X mode to be configured via a
> hardware strap. If this strap sets the default to "MDI-X off", the
> driver was previously unable to enable Auto-MDIX from userspace.
> 
> When handling the ETH_TP_MDI_AUTO case, the driver would set the
> SPECIAL_CTRL_STS_AMDIX_ENABLE_ bit but neglected to set the required
> SPECIAL_CTRL_STS_OVRRD_AMDIX_ bit. Without the override flag, the PHY
> falls back to its hardware strap default, ignoring the software request.
> 
> This patch corrects the behavior by also setting the override bit when
> enabling Auto-MDIX. This ensures that the userspace configuration takes
> precedence over the hardware strap, allowing Auto-MDIX to be enabled
> correctly in all scenarios.
> 
> Fixes: 05b35e7eb9a1 ("smsc95xx: add phylib support")
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> Cc: Andre Edich <andre.edich@microchip.com>

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime

Re: [PATCH net v2 2/3] net: phy: smsc: Force predictable MDI-X state on LAN87xx

[Maxime Chevallier]

On Thu,  3 Jul 2025 13:49:40 +0200
Oleksij Rempel <o.rempel@pengutronix.de> wrote:

> 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: 05b35e7eb9a1 ("smsc95xx: add phylib support")
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> Cc: Andre Edich <andre.edich@microchip.com>

The patch looks good to me, but I have a few questions.  As this
overrides some configuration on existing HW, and I'm not utra familiar
with auto-mdix, is there any chance this could cause regressions ?

Especially regarding your patch 3, is there any chance that the PHY is
strapped in a fixed MDIX mode to address the broken autoneg off mode ? 

I'm not saying that strapping is a good solution for that ofc :) it's a
shame we can't read the strap config :/

Maxime

Re: [PATCH net v2 2/3] net: phy: smsc: Force predictable MDI-X state on LAN87xx

[Andrew Lunn]

> The patch looks good to me, but I have a few questions.  As this
> overrides some configuration on existing HW, and I'm not utra familiar
> with auto-mdix, is there any chance this could cause regressions ?
> 
> Especially regarding your patch 3, is there any chance that the PHY is
> strapped in a fixed MDIX mode to address the broken autoneg off mode ? 
> 
> I'm not saying that strapping is a good solution for that ofc :) it's a
> shame we can't read the strap config :/

This might technically be considered a behaviour change. However there
are few systems which don't support it. It is also independent of
auto-neg, so autoneg off should not be an issue.

I think this is reasonably safe, and if somebody does report a
regression, we can revert the patch.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH net v2 3/3] net: phy: smsc: Fix link failure in forced mode with Auto-MDIX

[Andrew Lunn]

On Thu, Jul 03, 2025 at 01:49:41PM +0200, Oleksij Rempel wrote:
> Force a fixed MDI-X mode when auto-negotiation is disabled to prevent
> link instability.
> 
> When forcing the link speed and duplex on a LAN9500 PHY (e.g., with
> `ethtool -s eth0 autoneg off ...`) while leaving MDI-X control in auto
> mode, the PHY fails to establish a stable link. This occurs because the
> PHY's Auto-MDIX algorithm is not designed to operate when
> auto-negotiation is disabled. In this state, the PHY continuously
> toggles the TX/RX signal pairs, which prevents the link partner from
> synchronizing.

That is not good. Somebody got that badly wrong. They should operate
independently.

> This patch resolves the issue by detecting when auto-negotiation is
> disabled. If the MDI-X control mode is set to 'auto', the driver now
> forces a specific, stable mode (ETH_TP_MDI) to prevent the pair
> toggling. This choice of a fixed MDI mode mirrors the behavior the
> hardware would exhibit if the AUTOMDIX_EN strap were configured for a
> fixed MDI connection.

The text implies it, rather than states it, but the code supports
setting a fixed mode before turning autoneg off. So user space does
have full control if needed.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH net v2 0/4] net: phy: smsc: robustness fixes for LAN87xx/LAN9500

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  3 Jul 2025 13:49:38 +0200 you wrote:
> changes v2:
> - drop IRQ patch.
> - no other changes are made
> 
> Hi all,
> 
> The SMSC 10/100 PHYs (LAN87xx family) found in smsc95xx (lan95xx)
> USB-Ethernet adapters show several quirks around the Auto-MDIX feature:
> 
> [...]

Here is the summary with links:
  - [net,v2,1/3] net: phy: smsc: Fix Auto-MDIX configuration when disabled by strap
    https://git.kernel.org/netdev/net/c/a141af8eb227
  - [net,v2,2/3] net: phy: smsc: Force predictable MDI-X state on LAN87xx
    https://git.kernel.org/netdev/net/c/0713e55533c8
  - [net,v2,3/3] net: phy: smsc: Fix link failure in forced mode with Auto-MDIX
    https://git.kernel.org/netdev/net/c/9dfe110cc0f6

You are awesome, thank you!
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