[PATCH iwl-next v2 0/3] igc: add support for forcing link speed without autonegotiation

[PATCH iwl-next v2 0/3] igc: add support for forcing link speed without autonegotiation

[KhaiWenTan]

From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>

This series adds support for forcing 10/100 Mb/s link speed via ethtool
when autonegotiation is disabled on the igc driver.

Changes in v2:
- Simon Horman's review comment: when forcing half-duplex, set
  hw->fc.requested_mode = igc_fc_none, since half-duplex cannot support
  flow control per IEEE 802.3.
- Split the original single patch into three patches for clarity:
  patches 1 and 2 are preparatory cleanups; patch 3 carries the
  functional change.

v1 at:
https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20260409072747.217836-1-khai.wen.tan@linux.intel.com/

Faizal Rahim (3):
  igc: remove unused autoneg_failed field
  igc: move autoneg-enabled settings into igc_handle_autoneg_enabled()
  igc: add support for forcing link speed without autonegotiation

 drivers/net/ethernet/intel/igc/igc_base.c    |  35 +++-
 drivers/net/ethernet/intel/igc/igc_defines.h |   9 +-
 drivers/net/ethernet/intel/igc/igc_ethtool.c | 203 +++++++++++++------
 drivers/net/ethernet/intel/igc/igc_hw.h      |  10 +-
 drivers/net/ethernet/intel/igc/igc_mac.c     |  16 +-
 drivers/net/ethernet/intel/igc/igc_main.c    |   2 +-
 drivers/net/ethernet/intel/igc/igc_phy.c     |  65 +++++-
 drivers/net/ethernet/intel/igc/igc_phy.h     |   1 +
 8 files changed, 251 insertions(+), 90 deletions(-)

--
2.43.0

[PATCH iwl-next v2 1/3] igc: remove unused autoneg_failed field

[KhaiWenTan]

From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>

autoneg_failed in struct igc_mac_info is never set in the igc driver.
Remove the field and the dead code checking it in
igc_config_fc_after_link_up().

Reviewed-by: Looi, Hong Aun <hong.aun.looi@intel.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
---
 drivers/net/ethernet/intel/igc/igc_hw.h  |  1 -
 drivers/net/ethernet/intel/igc/igc_mac.c | 16 +---------------
 2 files changed, 1 insertion(+), 16 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_hw.h b/drivers/net/ethernet/intel/igc/igc_hw.h
index be8a49a86d09..86ab8f566f44 100644
--- a/drivers/net/ethernet/intel/igc/igc_hw.h
+++ b/drivers/net/ethernet/intel/igc/igc_hw.h
@@ -92,7 +92,6 @@ struct igc_mac_info {
 	bool asf_firmware_present;
 	bool arc_subsystem_valid;

-	bool autoneg_failed;
 	bool get_link_status;
 };

diff --git a/drivers/net/ethernet/intel/igc/igc_mac.c b/drivers/net/ethernet/intel/igc/igc_mac.c
index 7ac6637f8db7..142beb9ae557 100644
--- a/drivers/net/ethernet/intel/igc/igc_mac.c
+++ b/drivers/net/ethernet/intel/igc/igc_mac.c
@@ -438,28 +438,14 @@ void igc_config_collision_dist(struct igc_hw *hw)
  * Checks the status of auto-negotiation after link up to ensure that the
  * speed and duplex were not forced.  If the link needed to be forced, then
  * flow control needs to be forced also.  If auto-negotiation is enabled
- * and did not fail, then we configure flow control based on our link
- * partner.
+ * then we configure flow control based on our link partner.
  */
 s32 igc_config_fc_after_link_up(struct igc_hw *hw)
 {
 	u16 mii_status_reg, mii_nway_adv_reg, mii_nway_lp_ability_reg;
-	struct igc_mac_info *mac = &hw->mac;
 	u16 speed, duplex;
 	s32 ret_val = 0;

-	/* Check for the case where we have fiber media and auto-neg failed
-	 * so we had to force link.  In this case, we need to force the
-	 * configuration of the MAC to match the "fc" parameter.
-	 */
-	if (mac->autoneg_failed)
-		ret_val = igc_force_mac_fc(hw);
-
-	if (ret_val) {
-		hw_dbg("Error forcing flow control settings\n");
-		goto out;
-	}
-
 	/* In auto-neg, we need to check and see if Auto-Neg has completed,
 	 * and if so, how the PHY and link partner has flow control
 	 * configured.
--
2.43.0

RE: [Intel-wired-lan] [PATCH iwl-next v2 1/3] igc: remove unused autoneg_failed field

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> Of KhaiWenTan
> Sent: Thursday, April 16, 2026 3:55 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@intel.com>; andrew+netdev@lunn.ch;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com
> Cc: intel-wired-lan@lists.osuosl.org; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; Abdul Rahim, Faizal
> <faizal.abdul.rahim@intel.com>; Looi, Hong Aun
> <hong.aun.looi@intel.com>; Tan, Khai Wen <khai.wen.tan@intel.com>;
> Faizal Rahim <faizal.abdul.rahim@linux.intel.com>; Looi; KhaiWenTan
> <khai.wen.tan@linux.intel.com>
> Subject: [Intel-wired-lan] [PATCH iwl-next v2 1/3] igc: remove unused
> autoneg_failed field
> 
> From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
> 
> autoneg_failed in struct igc_mac_info is never set in the igc driver.
> Remove the field and the dead code checking it in
> igc_config_fc_after_link_up().
> 
> Reviewed-by: Looi, Hong Aun <hong.aun.looi@intel.com>
> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
> Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
> ---
>  drivers/net/ethernet/intel/igc/igc_hw.h  |  1 -
> drivers/net/ethernet/intel/igc/igc_mac.c | 16 +---------------
>  2 files changed, 1 insertion(+), 16 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_hw.h
> b/drivers/net/ethernet/intel/igc/igc_hw.h
> index be8a49a86d09..86ab8f566f44 100644
> --- a/drivers/net/ethernet/intel/igc/igc_hw.h
> +++ b/drivers/net/ethernet/intel/igc/igc_hw.h
> @@ -92,7 +92,6 @@ struct igc_mac_info {
>  	bool asf_firmware_present;
>  	bool arc_subsystem_valid;
> 
> -	bool autoneg_failed;
>  	bool get_link_status;
>  };
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_mac.c
> b/drivers/net/ethernet/intel/igc/igc_mac.c
> index 7ac6637f8db7..142beb9ae557 100644
> --- a/drivers/net/ethernet/intel/igc/igc_mac.c
> +++ b/drivers/net/ethernet/intel/igc/igc_mac.c
> @@ -438,28 +438,14 @@ void igc_config_collision_dist(struct igc_hw
> *hw)
>   * Checks the status of auto-negotiation after link up to ensure that
> the
>   * speed and duplex were not forced.  If the link needed to be
> forced, then
>   * flow control needs to be forced also.  If auto-negotiation is
> enabled
> - * and did not fail, then we configure flow control based on our link
> - * partner.
> + * then we configure flow control based on our link partner.
>   */
>  s32 igc_config_fc_after_link_up(struct igc_hw *hw)  {
>  	u16 mii_status_reg, mii_nway_adv_reg, mii_nway_lp_ability_reg;
> -	struct igc_mac_info *mac = &hw->mac;
>  	u16 speed, duplex;
>  	s32 ret_val = 0;
> 
> -	/* Check for the case where we have fiber media and auto-neg
> failed
> -	 * so we had to force link.  In this case, we need to force the
> -	 * configuration of the MAC to match the "fc" parameter.
> -	 */
> -	if (mac->autoneg_failed)
> -		ret_val = igc_force_mac_fc(hw);
> -
> -	if (ret_val) {
> -		hw_dbg("Error forcing flow control settings\n");
> -		goto out;
> -	}
> -
>  	/* In auto-neg, we need to check and see if Auto-Neg has
> completed,
>  	 * and if so, how the PHY and link partner has flow control
>  	 * configured.
> --
> 2.43.0

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>

[PATCH iwl-next v2 2/3] igc: move autoneg-enabled settings into igc_handle_autoneg_enabled()

[KhaiWenTan]

From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>

Move the advertised link modes and flow control configuration from
igc_ethtool_set_link_ksettings() into igc_handle_autoneg_enabled().

No functional change.

Reviewed-by: Looi, Hong Aun <hong.aun.looi@intel.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
---
 drivers/net/ethernet/intel/igc/igc_ethtool.c | 72 ++++++++++++--------
 1 file changed, 44 insertions(+), 28 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
index 0122009bedd0..cfcbf2fdad6e 100644
--- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
+++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
@@ -2000,6 +2000,49 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
 	return 0;
 }

+/**
+ * igc_handle_autoneg_enabled - Configure autonegotiation advertisement
+ * @adapter: private driver structure
+ * @cmd: ethtool link ksettings from user
+ *
+ * Records advertised speeds and flow control settings when autoneg
+ * is enabled.
+ */
+static void igc_handle_autoneg_enabled(struct igc_adapter *adapter,
+				       const struct ethtool_link_ksettings *cmd)
+{
+	struct igc_hw *hw = &adapter->hw;
+	u16 advertised = 0;
+
+	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
+						  2500baseT_Full))
+		advertised |= ADVERTISE_2500_FULL;
+
+	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
+						  1000baseT_Full))
+		advertised |= ADVERTISE_1000_FULL;
+
+	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
+						  100baseT_Full))
+		advertised |= ADVERTISE_100_FULL;
+
+	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
+						  100baseT_Half))
+		advertised |= ADVERTISE_100_HALF;
+
+	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
+						  10baseT_Full))
+		advertised |= ADVERTISE_10_FULL;
+
+	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
+						  10baseT_Half))
+		advertised |= ADVERTISE_10_HALF;
+
+	hw->phy.autoneg_advertised = advertised;
+	if (adapter->fc_autoneg)
+		hw->fc.requested_mode = igc_fc_default;
+}
+
 static int
 igc_ethtool_set_link_ksettings(struct net_device *netdev,
 			       const struct ethtool_link_ksettings *cmd)
@@ -2007,7 +2050,6 @@ igc_ethtool_set_link_ksettings(struct net_device *netdev,
 	struct igc_adapter *adapter = netdev_priv(netdev);
 	struct net_device *dev = adapter->netdev;
 	struct igc_hw *hw = &adapter->hw;
-	u16 advertised = 0;

 	/* When adapter in resetting mode, autoneg/speed/duplex
 	 * cannot be changed
@@ -2032,34 +2074,8 @@ igc_ethtool_set_link_ksettings(struct net_device *netdev,
 	while (test_and_set_bit(__IGC_RESETTING, &adapter->state))
 		usleep_range(1000, 2000);

-	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
-						  2500baseT_Full))
-		advertised |= ADVERTISE_2500_FULL;
-
-	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
-						  1000baseT_Full))
-		advertised |= ADVERTISE_1000_FULL;
-
-	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
-						  100baseT_Full))
-		advertised |= ADVERTISE_100_FULL;
-
-	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
-						  100baseT_Half))
-		advertised |= ADVERTISE_100_HALF;
-
-	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
-						  10baseT_Full))
-		advertised |= ADVERTISE_10_FULL;
-
-	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
-						  10baseT_Half))
-		advertised |= ADVERTISE_10_HALF;
-
 	if (cmd->base.autoneg == AUTONEG_ENABLE) {
-		hw->phy.autoneg_advertised = advertised;
-		if (adapter->fc_autoneg)
-			hw->fc.requested_mode = igc_fc_default;
+		igc_handle_autoneg_enabled(adapter, cmd);
 	} else {
 		netdev_info(dev, "Force mode currently not supported\n");
 	}
--
2.43.0

RE: [Intel-wired-lan] [PATCH iwl-next v2 2/3] igc: move autoneg-enabled settings into igc_handle_autoneg_enabled()

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> Of KhaiWenTan
> Sent: Thursday, April 16, 2026 3:55 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@intel.com>; andrew+netdev@lunn.ch;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com
> Cc: intel-wired-lan@lists.osuosl.org; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; Abdul Rahim, Faizal
> <faizal.abdul.rahim@intel.com>; Looi, Hong Aun
> <hong.aun.looi@intel.com>; Tan, Khai Wen <khai.wen.tan@intel.com>;
> Faizal Rahim <faizal.abdul.rahim@linux.intel.com>; Looi; KhaiWenTan
> <khai.wen.tan@linux.intel.com>
> Subject: [Intel-wired-lan] [PATCH iwl-next v2 2/3] igc: move autoneg-
> enabled settings into igc_handle_autoneg_enabled()
> 
> From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
> 
> Move the advertised link modes and flow control configuration from
> igc_ethtool_set_link_ksettings() into igc_handle_autoneg_enabled().
> 
> No functional change.
> 
> Reviewed-by: Looi, Hong Aun <hong.aun.looi@intel.com>
> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
> Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
> ---
>  drivers/net/ethernet/intel/igc/igc_ethtool.c | 72 ++++++++++++-------
> -
>  1 file changed, 44 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c
> b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> index 0122009bedd0..cfcbf2fdad6e 100644
> --- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
> +++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> @@ -2000,6 +2000,49 @@ static int
> igc_ethtool_get_link_ksettings(struct net_device *netdev,
>  	return 0;
>  }
> 
> +/**
> + * igc_handle_autoneg_enabled - Configure autonegotiation
> advertisement
> + * @adapter: private driver structure
> + * @cmd: ethtool link ksettings from user
> + *
> + * Records advertised speeds and flow control settings when autoneg
> + * is enabled.
> + */
> +static void igc_handle_autoneg_enabled(struct igc_adapter *adapter,
> +				       const struct ethtool_link_ksettings
> *cmd) {
> +	struct igc_hw *hw = &adapter->hw;
> +	u16 advertised = 0;
> +
> +	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> +						  2500baseT_Full))
> +		advertised |= ADVERTISE_2500_FULL;
> +
> +	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> +						  1000baseT_Full))
> +		advertised |= ADVERTISE_1000_FULL;
> +
> +	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> +						  100baseT_Full))
> +		advertised |= ADVERTISE_100_FULL;
> +
> +	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> +						  100baseT_Half))
> +		advertised |= ADVERTISE_100_HALF;
> +
> +	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> +						  10baseT_Full))
> +		advertised |= ADVERTISE_10_FULL;
> +
> +	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> +						  10baseT_Half))
> +		advertised |= ADVERTISE_10_HALF;
> +
> +	hw->phy.autoneg_advertised = advertised;
> +	if (adapter->fc_autoneg)
> +		hw->fc.requested_mode = igc_fc_default; }
> +
>  static int
>  igc_ethtool_set_link_ksettings(struct net_device *netdev,
>  			       const struct ethtool_link_ksettings *cmd)
> @@ -2007,7 +2050,6 @@ igc_ethtool_set_link_ksettings(struct net_device
> *netdev,
>  	struct igc_adapter *adapter = netdev_priv(netdev);
>  	struct net_device *dev = adapter->netdev;
>  	struct igc_hw *hw = &adapter->hw;
> -	u16 advertised = 0;
> 
>  	/* When adapter in resetting mode, autoneg/speed/duplex
>  	 * cannot be changed
> @@ -2032,34 +2074,8 @@ igc_ethtool_set_link_ksettings(struct
> net_device *netdev,
>  	while (test_and_set_bit(__IGC_RESETTING, &adapter->state))
>  		usleep_range(1000, 2000);
> 
> -	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> -						  2500baseT_Full))
> -		advertised |= ADVERTISE_2500_FULL;
> -
> -	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> -						  1000baseT_Full))
> -		advertised |= ADVERTISE_1000_FULL;
> -
> -	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> -						  100baseT_Full))
> -		advertised |= ADVERTISE_100_FULL;
> -
> -	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> -						  100baseT_Half))
> -		advertised |= ADVERTISE_100_HALF;
> -
> -	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> -						  10baseT_Full))
> -		advertised |= ADVERTISE_10_FULL;
> -
> -	if (ethtool_link_ksettings_test_link_mode(cmd, advertising,
> -						  10baseT_Half))
> -		advertised |= ADVERTISE_10_HALF;
> -
>  	if (cmd->base.autoneg == AUTONEG_ENABLE) {
> -		hw->phy.autoneg_advertised = advertised;
> -		if (adapter->fc_autoneg)
> -			hw->fc.requested_mode = igc_fc_default;
> +		igc_handle_autoneg_enabled(adapter, cmd);
>  	} else {
>  		netdev_info(dev, "Force mode currently not
> supported\n");
>  	}
> --
> 2.43.0


Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>

[PATCH iwl-next v2 3/3] igc: add support for forcing link speed without autonegotiation

[KhaiWenTan]

From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>

Allow users to force 10/100 Mb/s link speed and duplex via ethtool
when autonegotiation is disabled. Previously, the driver rejected
these requests with "Force mode currently not supported.".

Forcing at 1000 Mb/s and 2500 Mb/s is not supported.

Reviewed-by: Looi, Hong Aun <hong.aun.looi@intel.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Signed-off-by: KhaiWenTan <khai.wen.tan@linux.intel.com>
---
 drivers/net/ethernet/intel/igc/igc_base.c    |  35 ++++-
 drivers/net/ethernet/intel/igc/igc_defines.h |   9 +-
 drivers/net/ethernet/intel/igc/igc_ethtool.c | 131 +++++++++++++------
 drivers/net/ethernet/intel/igc/igc_hw.h      |   9 ++
 drivers/net/ethernet/intel/igc/igc_mac.c     |  10 ++
 drivers/net/ethernet/intel/igc/igc_main.c    |   2 +-
 drivers/net/ethernet/intel/igc/igc_phy.c     |  65 ++++++++-
 drivers/net/ethernet/intel/igc/igc_phy.h     |   1 +
 8 files changed, 211 insertions(+), 51 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_base.c b/drivers/net/ethernet/intel/igc/igc_base.c
index 1613b562d17c..ab9120a3127f 100644
--- a/drivers/net/ethernet/intel/igc/igc_base.c
+++ b/drivers/net/ethernet/intel/igc/igc_base.c
@@ -114,11 +114,35 @@ static s32 igc_setup_copper_link_base(struct igc_hw *hw)
 	u32 ctrl;

 	ctrl = rd32(IGC_CTRL);
-	ctrl |= IGC_CTRL_SLU;
-	ctrl &= ~(IGC_CTRL_FRCSPD | IGC_CTRL_FRCDPX);
-	wr32(IGC_CTRL, ctrl);
-
-	ret_val = igc_setup_copper_link(hw);
+	ctrl &= ~(IGC_CTRL_FRCSPD | IGC_CTRL_FRCDPX |
+		  IGC_CTRL_SPEED_MASK | IGC_CTRL_FD);
+
+	if (hw->mac.autoneg_enabled) {
+		ctrl |= IGC_CTRL_SLU;
+		wr32(IGC_CTRL, ctrl);
+		ret_val = igc_setup_copper_link(hw);
+	} else {
+		ctrl |= IGC_CTRL_SLU | IGC_CTRL_FRCSPD | IGC_CTRL_FRCDPX;
+
+		switch (hw->mac.forced_speed_duplex) {
+		case IGC_FORCED_10H:
+			ctrl |= IGC_CTRL_SPEED_10;
+			break;
+		case IGC_FORCED_10F:
+			ctrl |= IGC_CTRL_SPEED_10 | IGC_CTRL_FD;
+			break;
+		case IGC_FORCED_100H:
+			ctrl |= IGC_CTRL_SPEED_100;
+			break;
+		case IGC_FORCED_100F:
+			ctrl |= IGC_CTRL_SPEED_100 | IGC_CTRL_FD;
+			break;
+		default:
+			return -IGC_ERR_CONFIG;
+		}
+		wr32(IGC_CTRL, ctrl);
+		ret_val = igc_setup_copper_link(hw);
+	}

 	return ret_val;
 }
@@ -443,6 +467,7 @@ static const struct igc_phy_operations igc_phy_ops_base = {
 	.reset			= igc_phy_hw_reset,
 	.read_reg		= igc_read_phy_reg_gpy,
 	.write_reg		= igc_write_phy_reg_gpy,
+	.force_speed_duplex	= igc_force_speed_duplex,
 };

 const struct igc_info igc_base_info = {
diff --git a/drivers/net/ethernet/intel/igc/igc_defines.h b/drivers/net/ethernet/intel/igc/igc_defines.h
index 9482ab11f050..3f504751c2d9 100644
--- a/drivers/net/ethernet/intel/igc/igc_defines.h
+++ b/drivers/net/ethernet/intel/igc/igc_defines.h
@@ -129,10 +129,13 @@
 #define IGC_ERR_SWFW_SYNC		13

 /* Device Control */
+#define IGC_CTRL_FD		BIT(0)  /* Full Duplex */
 #define IGC_CTRL_RST		0x04000000  /* Global reset */
-
 #define IGC_CTRL_PHY_RST	0x80000000  /* PHY Reset */
 #define IGC_CTRL_SLU		0x00000040  /* Set link up (Force Link) */
+#define IGC_CTRL_SPEED_MASK	GENMASK(10, 8)
+#define IGC_CTRL_SPEED_10	FIELD_PREP(IGC_CTRL_SPEED_MASK, 0)
+#define IGC_CTRL_SPEED_100	FIELD_PREP(IGC_CTRL_SPEED_MASK, 1)
 #define IGC_CTRL_FRCSPD		0x00000800  /* Force Speed */
 #define IGC_CTRL_FRCDPX		0x00001000  /* Force Duplex */
 #define IGC_CTRL_VME		0x40000000  /* IEEE VLAN mode enable */
@@ -673,6 +676,10 @@
 #define IGC_GEN_POLL_TIMEOUT	1920

 /* PHY Control Register */
+#define MII_CR_SPEED_MASK	(BIT(6) | BIT(13))
+#define MII_CR_SPEED_10		0x0000	/* SSM=0, SSL=0: 10 Mb/s */
+#define MII_CR_SPEED_100	BIT(13)	/* SSM=0, SSL=1: 100 Mb/s */
+#define MII_CR_DUPLEX_EN	BIT(8)	/* 0 = Half Duplex, 1 = Full Duplex */
 #define MII_CR_RESTART_AUTO_NEG	0x0200  /* Restart auto negotiation */
 #define MII_CR_POWER_DOWN	0x0800  /* Power down */
 #define MII_CR_AUTO_NEG_EN	0x1000  /* Auto Neg Enable */
diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
index cfcbf2fdad6e..5bd37d1be168 100644
--- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
+++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
@@ -1914,44 +1914,58 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
 	ethtool_link_ksettings_add_link_mode(cmd, supported, TP);
 	ethtool_link_ksettings_add_link_mode(cmd, advertising, TP);

-	/* advertising link modes */
-	if (hw->phy.autoneg_advertised & ADVERTISE_10_HALF)
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, 10baseT_Half);
-	if (hw->phy.autoneg_advertised & ADVERTISE_10_FULL)
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, 10baseT_Full);
-	if (hw->phy.autoneg_advertised & ADVERTISE_100_HALF)
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, 100baseT_Half);
-	if (hw->phy.autoneg_advertised & ADVERTISE_100_FULL)
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, 100baseT_Full);
-	if (hw->phy.autoneg_advertised & ADVERTISE_1000_FULL)
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, 1000baseT_Full);
-	if (hw->phy.autoneg_advertised & ADVERTISE_2500_FULL)
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, 2500baseT_Full);
-
 	/* set autoneg settings */
 	ethtool_link_ksettings_add_link_mode(cmd, supported, Autoneg);
-	ethtool_link_ksettings_add_link_mode(cmd, advertising, Autoneg);
+	if (hw->mac.autoneg_enabled) {
+		ethtool_link_ksettings_add_link_mode(cmd, advertising, Autoneg);
+		cmd->base.autoneg = AUTONEG_ENABLE;
+
+		/* advertising link modes only apply when autoneg is on */
+		if (hw->phy.autoneg_advertised & ADVERTISE_10_HALF)
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     10baseT_Half);
+		if (hw->phy.autoneg_advertised & ADVERTISE_10_FULL)
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     10baseT_Full);
+		if (hw->phy.autoneg_advertised & ADVERTISE_100_HALF)
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     100baseT_Half);
+		if (hw->phy.autoneg_advertised & ADVERTISE_100_FULL)
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     100baseT_Full);
+		if (hw->phy.autoneg_advertised & ADVERTISE_1000_FULL)
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     1000baseT_Full);
+		if (hw->phy.autoneg_advertised & ADVERTISE_2500_FULL)
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     2500baseT_Full);
+
+		/* Set pause flow control advertising */
+		switch (hw->fc.requested_mode) {
+		case igc_fc_full:
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     Pause);
+			break;
+		case igc_fc_rx_pause:
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     Pause);
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     Asym_Pause);
+			break;
+		case igc_fc_tx_pause:
+			ethtool_link_ksettings_add_link_mode(cmd, advertising,
+							     Asym_Pause);
+			break;
+		default:
+			break;
+		}
+	} else {
+		cmd->base.autoneg = AUTONEG_DISABLE;
+	}

-	/* Set pause flow control settings */
+	/* Pause is always supported */
 	ethtool_link_ksettings_add_link_mode(cmd, supported, Pause);

-	switch (hw->fc.requested_mode) {
-	case igc_fc_full:
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, Pause);
-		break;
-	case igc_fc_rx_pause:
-		ethtool_link_ksettings_add_link_mode(cmd, advertising, Pause);
-		ethtool_link_ksettings_add_link_mode(cmd, advertising,
-						     Asym_Pause);
-		break;
-	case igc_fc_tx_pause:
-		ethtool_link_ksettings_add_link_mode(cmd, advertising,
-						     Asym_Pause);
-		break;
-	default:
-		break;
-	}
-
 	status = pm_runtime_suspended(&adapter->pdev->dev) ?
 		 0 : rd32(IGC_STATUS);

@@ -1983,7 +1997,6 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
 		cmd->base.duplex = DUPLEX_UNKNOWN;
 	}
 	cmd->base.speed = speed;
-	cmd->base.autoneg = AUTONEG_ENABLE;

 	/* MDI-X => 2; MDI =>1; Invalid =>0 */
 	if (hw->phy.media_type == igc_media_type_copper)
@@ -2000,6 +2013,41 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
 	return 0;
 }

+/**
+ * igc_handle_autoneg_disabled - Configure forced speed/duplex settings
+ * @adapter: private driver structure
+ * @speed: requested speed (must be SPEED_10 or SPEED_100)
+ * @duplex: requested duplex
+ *
+ * Records forced speed/duplex when autoneg is disabled.
+ * Caller must validate speed before calling this function.
+ */
+static void igc_handle_autoneg_disabled(struct igc_adapter *adapter, u32 speed,
+					u8 duplex)
+{
+	struct igc_mac_info *mac = &adapter->hw.mac;
+
+	switch (speed) {
+	case SPEED_10:
+		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
+			IGC_FORCED_10F : IGC_FORCED_10H;
+		break;
+	case SPEED_100:
+		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
+			IGC_FORCED_100F : IGC_FORCED_100H;
+		break;
+	default:
+		WARN_ONCE(1, "Unsupported speed %u\n", speed);
+		return;
+	}
+
+	mac->autoneg_enabled = false;
+
+	/* Half-duplex cannot support flow control per IEEE 802.3 */
+	if (duplex == DUPLEX_HALF)
+		adapter->hw.fc.requested_mode = igc_fc_none;
+}
+
 /**
  * igc_handle_autoneg_enabled - Configure autonegotiation advertisement
  * @adapter: private driver structure
@@ -2038,6 +2086,7 @@ static void igc_handle_autoneg_enabled(struct igc_adapter *adapter,
 						  10baseT_Half))
 		advertised |= ADVERTISE_10_HALF;

+	hw->mac.autoneg_enabled = true;
 	hw->phy.autoneg_advertised = advertised;
 	if (adapter->fc_autoneg)
 		hw->fc.requested_mode = igc_fc_default;
@@ -2071,14 +2120,20 @@ igc_ethtool_set_link_ksettings(struct net_device *netdev,
 		}
 	}

+	if (cmd->base.autoneg == AUTONEG_DISABLE &&
+	    cmd->base.speed != SPEED_10 && cmd->base.speed != SPEED_100) {
+		netdev_info(dev, "Unsupported speed for forced link\n");
+		return -EINVAL;
+	}
+
 	while (test_and_set_bit(__IGC_RESETTING, &adapter->state))
 		usleep_range(1000, 2000);

-	if (cmd->base.autoneg == AUTONEG_ENABLE) {
+	if (cmd->base.autoneg == AUTONEG_ENABLE)
 		igc_handle_autoneg_enabled(adapter, cmd);
-	} else {
-		netdev_info(dev, "Force mode currently not supported\n");
-	}
+	else
+		igc_handle_autoneg_disabled(adapter, cmd->base.speed,
+					    cmd->base.duplex);

 	/* MDI-X => 2; MDI => 1; Auto => 3 */
 	if (cmd->base.eth_tp_mdix_ctrl) {
diff --git a/drivers/net/ethernet/intel/igc/igc_hw.h b/drivers/net/ethernet/intel/igc/igc_hw.h
index 86ab8f566f44..62aaee55668a 100644
--- a/drivers/net/ethernet/intel/igc/igc_hw.h
+++ b/drivers/net/ethernet/intel/igc/igc_hw.h
@@ -73,6 +73,13 @@ struct igc_info {

 extern const struct igc_info igc_base_info;

+enum igc_forced_speed_duplex {
+	IGC_FORCED_10H,
+	IGC_FORCED_10F,
+	IGC_FORCED_100H,
+	IGC_FORCED_100F,
+};
+
 struct igc_mac_info {
 	struct igc_mac_operations ops;

@@ -93,6 +100,8 @@ struct igc_mac_info {
 	bool arc_subsystem_valid;

 	bool get_link_status;
+	bool autoneg_enabled;
+	enum igc_forced_speed_duplex forced_speed_duplex;
 };

 struct igc_nvm_operations {
diff --git a/drivers/net/ethernet/intel/igc/igc_mac.c b/drivers/net/ethernet/intel/igc/igc_mac.c
index 142beb9ae557..8bbb6d5581c7 100644
--- a/drivers/net/ethernet/intel/igc/igc_mac.c
+++ b/drivers/net/ethernet/intel/igc/igc_mac.c
@@ -446,6 +446,16 @@ s32 igc_config_fc_after_link_up(struct igc_hw *hw)
 	u16 speed, duplex;
 	s32 ret_val = 0;

+	/* When autoneg is disabled, force the MAC flow control settings
+	 * to match the "fc" parameter.
+	 */
+	if (!hw->mac.autoneg_enabled) {
+		ret_val = igc_force_mac_fc(hw);
+		if (ret_val)
+			hw_dbg("Error forcing flow control settings\n");
+		goto out;
+	}
+
 	/* In auto-neg, we need to check and see if Auto-Neg has completed,
 	 * and if so, how the PHY and link partner has flow control
 	 * configured.
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 72bc5128d8b8..437e1d1ef1e4 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -7298,7 +7298,7 @@ static int igc_probe(struct pci_dev *pdev,
 	/* Initialize link properties that are user-changeable */
 	adapter->fc_autoneg = true;
 	hw->phy.autoneg_advertised = 0xaf;
-
+	hw->mac.autoneg_enabled = true;
 	hw->fc.requested_mode = igc_fc_default;
 	hw->fc.current_mode = igc_fc_default;

diff --git a/drivers/net/ethernet/intel/igc/igc_phy.c b/drivers/net/ethernet/intel/igc/igc_phy.c
index 6c4d204aecfa..4cf737fb3b21 100644
--- a/drivers/net/ethernet/intel/igc/igc_phy.c
+++ b/drivers/net/ethernet/intel/igc/igc_phy.c
@@ -494,12 +494,20 @@ s32 igc_setup_copper_link(struct igc_hw *hw)
 	s32 ret_val = 0;
 	bool link;

-	/* Setup autoneg and flow control advertisement and perform
-	 * autonegotiation.
-	 */
-	ret_val = igc_copper_link_autoneg(hw);
-	if (ret_val)
-		goto out;
+	if (hw->mac.autoneg_enabled) {
+		/* Setup autoneg and flow control advertisement and perform
+		 * autonegotiation.
+		 */
+		ret_val = igc_copper_link_autoneg(hw);
+		if (ret_val)
+			goto out;
+	} else {
+		ret_val = hw->phy.ops.force_speed_duplex(hw);
+		if (ret_val) {
+			hw_dbg("Error Forcing Speed/Duplex\n");
+			goto out;
+		}
+	}

 	/* Check link status. Wait up to 100 microseconds for link to become
 	 * valid.
@@ -778,3 +786,48 @@ u16 igc_read_phy_fw_version(struct igc_hw *hw)

 	return gphy_version;
 }
+
+/**
+ * igc_force_speed_duplex - Force PHY speed and duplex settings
+ * @hw: pointer to the HW structure
+ *
+ * Programs the GPY PHY control register to disable autonegotiation
+ * and force the speed/duplex indicated by hw->mac.forced_speed_duplex.
+ */
+s32 igc_force_speed_duplex(struct igc_hw *hw)
+{
+	struct igc_phy_info *phy = &hw->phy;
+	u16 phy_ctrl;
+	s32 ret_val;
+
+	ret_val = phy->ops.read_reg(hw, PHY_CONTROL, &phy_ctrl);
+	if (ret_val)
+		return ret_val;
+
+	phy_ctrl &= ~(MII_CR_SPEED_MASK | MII_CR_DUPLEX_EN |
+		      MII_CR_AUTO_NEG_EN | MII_CR_RESTART_AUTO_NEG);
+
+	switch (hw->mac.forced_speed_duplex) {
+	case IGC_FORCED_10H:
+		phy_ctrl |= MII_CR_SPEED_10;
+		break;
+	case IGC_FORCED_10F:
+		phy_ctrl |= MII_CR_SPEED_10 | MII_CR_DUPLEX_EN;
+		break;
+	case IGC_FORCED_100H:
+		phy_ctrl |= MII_CR_SPEED_100;
+		break;
+	case IGC_FORCED_100F:
+		phy_ctrl |= MII_CR_SPEED_100 | MII_CR_DUPLEX_EN;
+		break;
+	default:
+		return -IGC_ERR_CONFIG;
+	}
+
+	ret_val = phy->ops.write_reg(hw, PHY_CONTROL, phy_ctrl);
+	if (ret_val)
+		return ret_val;
+
+	hw->mac.get_link_status = true;
+	return 0;
+}
diff --git a/drivers/net/ethernet/intel/igc/igc_phy.h b/drivers/net/ethernet/intel/igc/igc_phy.h
index 832a7e359f18..d37a89174826 100644
--- a/drivers/net/ethernet/intel/igc/igc_phy.h
+++ b/drivers/net/ethernet/intel/igc/igc_phy.h
@@ -18,5 +18,6 @@ void igc_power_down_phy_copper(struct igc_hw *hw);
 s32 igc_write_phy_reg_gpy(struct igc_hw *hw, u32 offset, u16 data);
 s32 igc_read_phy_reg_gpy(struct igc_hw *hw, u32 offset, u16 *data);
 u16 igc_read_phy_fw_version(struct igc_hw *hw);
+s32 igc_force_speed_duplex(struct igc_hw *hw);

 #endif
--
2.43.0

Re: [PATCH iwl-next v2 3/3] igc: add support for forcing link speed without autonegotiation

[Simon Horman]

From: 'Simon Horman' <horms@kernel.org>

This is an AI-generated review of your patch. The human sending this
email has considered the AI review valid, or at least plausible.
Full review at: https://sashiko.dev
---
igc: add support for forcing link speed without autonegotiation

This commit adds support to allow users to force 10/100 Mb/s link speed
and duplex via ethtool when autonegotiation is disabled.

> diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> index cfcbf2fdad6ea..5bd37d1be1688 100644
> --- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
> +++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c

[ ... ]

> @@ -2000,6 +2013,41 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
>  	return 0;
>  }
>  
> +/**
> + * igc_handle_autoneg_disabled - Configure forced speed/duplex settings
> + * @adapter: private driver structure
> + * @speed: requested speed (must be SPEED_10 or SPEED_100)
> + * @duplex: requested duplex
> + *
> + * Records forced speed/duplex when autoneg is disabled.
> + * Caller must validate speed before calling this function.
> + */
> +static void igc_handle_autoneg_disabled(struct igc_adapter *adapter, u32 speed,
> +					u8 duplex)
> +{
> +	struct igc_mac_info *mac = &adapter->hw.mac;
> +
> +	switch (speed) {
> +	case SPEED_10:
> +		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
> +			IGC_FORCED_10F : IGC_FORCED_10H;
> +		break;
> +	case SPEED_100:
> +		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
> +			IGC_FORCED_100F : IGC_FORCED_100H;
> +		break;
> +	default:
> +		WARN_ONCE(1, "Unsupported speed %u\n", speed);
> +		return;
> +	}
> +
> +	mac->autoneg_enabled = false;
> +
> +	/* Half-duplex cannot support flow control per IEEE 802.3 */
> +	if (duplex == DUPLEX_HALF)
> +		adapter->hw.fc.requested_mode = igc_fc_none;
> +}

If userspace issues an ethtool command without specifying duplex, the duplex
value can be DUPLEX_UNKNOWN. In this case, forced_speed_duplex correctly
defaults to half-duplex since duplex == DUPLEX_FULL evaluates to false. 

However, since DUPLEX_UNKNOWN is not equal to DUPLEX_HALF, the check above
fails, and the requested flow control mode remains unchanged. Could this leave
flow control enabled on a forced half-duplex link, violating IEEE 802.3?
Should this check be based on the resolved mac->forced_speed_duplex state
instead?

[ ... ]

> @@ -2071,14 +2120,20 @@ igc_ethtool_set_link_ksettings(struct net_device *netdev,
>  		}
>  	}
>  
> +	if (cmd->base.autoneg == AUTONEG_DISABLE &&
> +	    cmd->base.speed != SPEED_10 && cmd->base.speed != SPEED_100) {
> +		netdev_info(dev, "Unsupported speed for forced link\n");
> +		return -EINVAL;
> +	}
> +
>  	while (test_and_set_bit(__IGC_RESETTING, &adapter->state))
>  		usleep_range(1000, 2000);

This isn't a bug introduced by this patch, but does this ad-hoc
synchronization using bit flags circumvent proper locking guarantees? The
networking subsystem guidelines forbid using bit flags as ad-hoc locks. 

Using a bit flag in a polling loop bypasses lockdep analysis, fairness, and
strict memory ordering. Could this be replaced with a real synchronization
mechanism like a mutex?

Re: [PATCH iwl-next v2 3/3] igc: add support for forcing link speed without autonegotiation

[Abdul Rahim, Faizal]

On 19/4/2026 12:48 am, Simon Horman wrote:
> From: 'Simon Horman' <horms@kernel.org>
> 
> This is an AI-generated review of your patch. The human sending this
> email has considered the AI review valid, or at least plausible.
> Full review at: https://sashiko.dev
> ---
> igc: add support for forcing link speed without autonegotiation
> 
> This commit adds support to allow users to force 10/100 Mb/s link speed
> and duplex via ethtool when autonegotiation is disabled.
> 
>> diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
>> index cfcbf2fdad6ea..5bd37d1be1688 100644
>> --- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
>> +++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> 
> [ ... ]
> 
>> @@ -2000,6 +2013,41 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
>>   	return 0;
>>   }
>>   
>> +/**
>> + * igc_handle_autoneg_disabled - Configure forced speed/duplex settings
>> + * @adapter: private driver structure
>> + * @speed: requested speed (must be SPEED_10 or SPEED_100)
>> + * @duplex: requested duplex
>> + *
>> + * Records forced speed/duplex when autoneg is disabled.
>> + * Caller must validate speed before calling this function.
>> + */
>> +static void igc_handle_autoneg_disabled(struct igc_adapter *adapter, u32 speed,
>> +					u8 duplex)
>> +{
>> +	struct igc_mac_info *mac = &adapter->hw.mac;
>> +
>> +	switch (speed) {
>> +	case SPEED_10:
>> +		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
>> +			IGC_FORCED_10F : IGC_FORCED_10H;
>> +		break;
>> +	case SPEED_100:
>> +		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
>> +			IGC_FORCED_100F : IGC_FORCED_100H;
>> +		break;
>> +	default:
>> +		WARN_ONCE(1, "Unsupported speed %u\n", speed);
>> +		return;
>> +	}
>> +
>> +	mac->autoneg_enabled = false;
>> +
>> +	/* Half-duplex cannot support flow control per IEEE 802.3 */
>> +	if (duplex == DUPLEX_HALF)
>> +		adapter->hw.fc.requested_mode = igc_fc_none;
>> +}
> 
> If userspace issues an ethtool command without specifying duplex, the duplex
> value can be DUPLEX_UNKNOWN. In this case, forced_speed_duplex correctly
> defaults to half-duplex since duplex == DUPLEX_FULL evaluates to false.
> 
> However, since DUPLEX_UNKNOWN is not equal to DUPLEX_HALF, the check above
> fails, and the requested flow control mode remains unchanged. Could this leave
> flow control enabled on a forced half-duplex link, violating IEEE 802.3?
> Should this check be based on the resolved mac->forced_speed_duplex state
> instead?
>

You're right, thanks for pointing that out.

That said, it feels simpler to address it with [1]:
if (duplex != DUPLEX_FULL)
     adapter->hw.fc.requested_mode = igc_fc_none;

Rather than [2]:
  if (mac->forced_speed_duplex == IGC_FORCED_10H ||
         mac->forced_speed_duplex == IGC_FORCED_100H)
         adapter->hw.fc.requested_mode = igc_fc_none;

Are you okay with [1] ?

> [ ... ]
> 
>> @@ -2071,14 +2120,20 @@ igc_ethtool_set_link_ksettings(struct net_device *netdev,
>>   		}
>>   	}
>>   
>> +	if (cmd->base.autoneg == AUTONEG_DISABLE &&
>> +	    cmd->base.speed != SPEED_10 && cmd->base.speed != SPEED_100) {
>> +		netdev_info(dev, "Unsupported speed for forced link\n");
>> +		return -EINVAL;
>> +	}
>> +
>>   	while (test_and_set_bit(__IGC_RESETTING, &adapter->state))
>>   		usleep_range(1000, 2000);
> 
> This isn't a bug introduced by this patch, but does this ad-hoc
> synchronization using bit flags circumvent proper locking guarantees? The
> networking subsystem guidelines forbid using bit flags as ad-hoc locks.
> 
> Using a bit flag in a polling loop bypasses lockdep analysis, fairness, and
> strict memory ordering. Could this be replaced with a real synchronization
> mechanism like a mutex?

It looks like a worthwhile cleanup. However, it likely doesn’t belong in 
this series, since the synchronization pattern predates these patches and 
is used throughout the igc driver (set_ringparam, set_pauseparam, 
set_channels, etc.). We could address it in different patch series and 
align the other code paths at the same time ?

Re: [PATCH iwl-next v2 3/3] igc: add support for forcing link speed without autonegotiation

[Simon Horman]

On Mon, Apr 20, 2026 at 11:20:07AM +0800, Abdul Rahim, Faizal wrote:
> 
> 
> On 19/4/2026 12:48 am, Simon Horman wrote:
> > From: 'Simon Horman' <horms@kernel.org>
> > 
> > This is an AI-generated review of your patch. The human sending this
> > email has considered the AI review valid, or at least plausible.
> > Full review at: https://sashiko.dev
> > ---
> > igc: add support for forcing link speed without autonegotiation
> > 
> > This commit adds support to allow users to force 10/100 Mb/s link speed
> > and duplex via ethtool when autonegotiation is disabled.
> > 
> > > diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> > > index cfcbf2fdad6ea..5bd37d1be1688 100644
> > > --- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
> > > +++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> > 
> > [ ... ]
> > 
> > > @@ -2000,6 +2013,41 @@ static int igc_ethtool_get_link_ksettings(struct net_device *netdev,
> > >   	return 0;
> > >   }
> > > +/**
> > > + * igc_handle_autoneg_disabled - Configure forced speed/duplex settings
> > > + * @adapter: private driver structure
> > > + * @speed: requested speed (must be SPEED_10 or SPEED_100)
> > > + * @duplex: requested duplex
> > > + *
> > > + * Records forced speed/duplex when autoneg is disabled.
> > > + * Caller must validate speed before calling this function.
> > > + */
> > > +static void igc_handle_autoneg_disabled(struct igc_adapter *adapter, u32 speed,
> > > +					u8 duplex)
> > > +{
> > > +	struct igc_mac_info *mac = &adapter->hw.mac;
> > > +
> > > +	switch (speed) {
> > > +	case SPEED_10:
> > > +		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
> > > +			IGC_FORCED_10F : IGC_FORCED_10H;
> > > +		break;
> > > +	case SPEED_100:
> > > +		mac->forced_speed_duplex = (duplex == DUPLEX_FULL) ?
> > > +			IGC_FORCED_100F : IGC_FORCED_100H;
> > > +		break;
> > > +	default:
> > > +		WARN_ONCE(1, "Unsupported speed %u\n", speed);
> > > +		return;
> > > +	}
> > > +
> > > +	mac->autoneg_enabled = false;
> > > +
> > > +	/* Half-duplex cannot support flow control per IEEE 802.3 */
> > > +	if (duplex == DUPLEX_HALF)
> > > +		adapter->hw.fc.requested_mode = igc_fc_none;
> > > +}
> > 
> > If userspace issues an ethtool command without specifying duplex, the duplex
> > value can be DUPLEX_UNKNOWN. In this case, forced_speed_duplex correctly
> > defaults to half-duplex since duplex == DUPLEX_FULL evaluates to false.
> > 
> > However, since DUPLEX_UNKNOWN is not equal to DUPLEX_HALF, the check above
> > fails, and the requested flow control mode remains unchanged. Could this leave
> > flow control enabled on a forced half-duplex link, violating IEEE 802.3?
> > Should this check be based on the resolved mac->forced_speed_duplex state
> > instead?
> > 
> 
> You're right, thanks for pointing that out.
> 
> That said, it feels simpler to address it with [1]:
> if (duplex != DUPLEX_FULL)
>     adapter->hw.fc.requested_mode = igc_fc_none;
> 
> Rather than [2]:
>  if (mac->forced_speed_duplex == IGC_FORCED_10H ||
>         mac->forced_speed_duplex == IGC_FORCED_100H)
>         adapter->hw.fc.requested_mode = igc_fc_none;
> 
> Are you okay with [1] ?

Yes, [1] sounds sensible to me.

> 
> > [ ... ]
> > 
> > > @@ -2071,14 +2120,20 @@ igc_ethtool_set_link_ksettings(struct net_device *netdev,
> > >   		}
> > >   	}
> > > +	if (cmd->base.autoneg == AUTONEG_DISABLE &&
> > > +	    cmd->base.speed != SPEED_10 && cmd->base.speed != SPEED_100) {
> > > +		netdev_info(dev, "Unsupported speed for forced link\n");
> > > +		return -EINVAL;
> > > +	}
> > > +
> > >   	while (test_and_set_bit(__IGC_RESETTING, &adapter->state))
> > >   		usleep_range(1000, 2000);
> > 
> > This isn't a bug introduced by this patch, but does this ad-hoc
> > synchronization using bit flags circumvent proper locking guarantees? The
> > networking subsystem guidelines forbid using bit flags as ad-hoc locks.
> > 
> > Using a bit flag in a polling loop bypasses lockdep analysis, fairness, and
> > strict memory ordering. Could this be replaced with a real synchronization
> > mechanism like a mutex?
> 
> It looks like a worthwhile cleanup. However, it likely doesn’t belong in
> this series, since the synchronization pattern predates these patches and is
> used throughout the igc driver (set_ringparam, set_pauseparam, set_channels,
> etc.). We could address it in different patch series and align the other
> code paths at the same time ?

Yes, agreed.