On 19/4/2026 12:48 am, Simon Horman wrote:
From: 'Simon Horman' <[email protected]>
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 ?
