Re: [PATCH iwl-next v3 3/3] igc: add support for forcing link speed without autonegotiation

["Abdul Rahim, Faizal" <faizal.abdul.rahim@linux.intel.com>]

On 24/4/2026 9:59 pm, Simon Horman wrote:
> On Wed, Apr 22, 2026 at 11:57:01PM +0800, KhaiWenTan wrote:
>> 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>
> 
> ...
> 
>> diff --git 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_FULL)
>> +		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;
>> +	}
> 
> The condition above verifies speed only if autoneg is AUTONEG_DISABLE.
> 
>> +
>>   	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);
> 
> But here igc_handle_autoneg_disabled, which relies on speed having been
> verified, is called if autoneg is not AUTONEG_ENABLE.
> 
> If autoneg is AUTONEG_DISABLE here, then all is good.
> But if it is neither AUTONEG_DISABLE nor AUTONEG_ENABLE then we
> are in trouble.
> 
> I suggest verifying autoneg is either AUTONEG_ENABLE or AUTONEG_DISABLE
> earlier in this function.

Will update, thanks.