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

[Abdul Rahim, Faizal]

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@xxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > Signed-off-by: Faizal Rahim <faizal.abdul.rahim@xxxxxxxxxxxxxxx>
> > Signed-off-by: KhaiWenTan <khai.wen.tan@xxxxxxxxxxxxxxx>
>
> ...
>
> > 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.