[igb] add DROP_EN to each RX queue config if TX flow control is disabled

[Adrian Chadd]

Hi,

This patch enables the DROP_EN flag to each RX queue if TX flow
control is disabled. It (mostly) mirrors what the ixgbe driver does.

This prevents a single full RX ring from stalling the rest of the RX rings.

How's it look? (indenting and such aside, thanks google.)



-a

Index: sys/dev/e1000/if_igb.c
===================================================================
--- sys/dev/e1000/if_igb.c (revision 271290)
+++ sys/dev/e1000/if_igb.c (working copy)
@@ -4712,6 +4712,18 @@
  rctl |= E1000_RCTL_SZ_2048;
  }

+ /*
+ * If TX flow control is disabled and there's >1 queue defined,
+ * enable DROP.
+ *
+ * This drops frames rather than hanging the RX MAC for all queues.
+ */
+ if ((adapter->num_queues > 1) &&
+     (adapter->fc == e1000_fc_none ||
+     adapter->fc == e1000_fc_rx_pause)) {
+        srrctl |= E1000_SRRCTL_DROP_EN;
+ }
+
  /* Setup the Base and Length of the Rx Descriptor Rings */
  for (int i = 0; i < adapter->num_queues; i++, rxr++) {
  u64 bus_addr = rxr->rxdma.dma_paddr;
@@ -6255,6 +6267,7 @@

  adapter->hw.fc.current_mode = adapter->hw.fc.requested_mode;
  e1000_force_mac_fc(&adapter->hw);
+ /* XXX TODO: update DROP_EN on each RX queue if appropriate */
  return (error);
 }