e1000e: fix the use of magic numbers for buffer overrun issue

This is a follow on to commit b10effb92e27 ("fix buffer overrun while the
 I219 is processing DMA transactions") to address David Laights concerns
about the use of "magic" numbers.  So define masks as well as add
additional code comments to give a better understanding of what needs to
be done to avoid a buffer overrun.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Reviewed-by: Alexander H Duyck <alexander.h.duyck@intel.com>
Reviewed-by: Dima Ruinskiy <dima.ruinskiy@intel.com>
Reviewed-by: Raanan Avargil <raanan.avargil@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
index f2f49239b015..9f18d39bdc8f 100644
--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
@@ -3034,9 +3034,12 @@ static void e1000_configure_tx(struct e1000_adapter *adapter)
 		ew32(IOSFPC, reg_val);
 
 		reg_val = er32(TARC(0));
-		/* SPT and KBL Si errata workaround to avoid Tx hang */
-		reg_val &= ~BIT(28);
-		reg_val |= BIT(29);
+		/* SPT and KBL Si errata workaround to avoid Tx hang.
+		 * Dropping the number of outstanding requests from
+		 * 3 to 2 in order to avoid a buffer overrun.
+		 */
+		reg_val &= ~E1000_TARC0_CB_MULTIQ_3_REQ;
+		reg_val |= E1000_TARC0_CB_MULTIQ_2_REQ;
 		ew32(TARC(0), reg_val);
 	}
 }