e1000e: correct flow control thresholds

The flow control thresholds, i.e. high and low watermarks of the Rx
FIFO for when the hardware should transmit PAUSE frames (XON and XOFF,
respectively), need to be tuned for more efficient use of the FIFO.
The logic to set the thresholds for parts that support early-receive
(ERT) was also wrong in that it should check whether jumbo frames are
in use.
Signed-off-by: NBruce Allan <bruce.w.allan@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/e1000e/defines.h

@@ -469,6 +469,8 @@
 #define AUTO_READ_DONE_TIMEOUT      10
 
 /* Flow Control */
+#define E1000_FCRTH_RTH  0x0000FFF8     /* Mask Bits[15:3] for RTH */
+#define E1000_FCRTL_RTL  0x0000FFF8     /* Mask Bits[15:3] for RTL */
 #define E1000_FCRTL_XONE 0x80000000     /* Enable XON frame transmission */
 
 /* Transmit Configuration Word */

drivers/net/e1000e/netdev.c

@@ -2751,23 +2751,25 @@ void e1000e_reset(struct e1000_adapter *adapter)
 	/*
 	 * flow control settings
 	 *
-	 * The high water mark must be low enough to fit one full frame
+	 * The high water mark must be low enough to fit two full frame
 	 * (or the size used for early receive) above it in the Rx FIFO.
 	 * Set it to the lower of:
 	 * - 90% of the Rx FIFO size, and
 	 * - the full Rx FIFO size minus the early receive size (for parts
 	 *   with ERT support assuming ERT set to E1000_ERT_2048), or
-	 * - the full Rx FIFO size minus one full frame
+	 * - the full Rx FIFO size minus two full frames
 	 */
-	if (adapter->flags & FLAG_HAS_ERT)
+	if ((adapter->flags & FLAG_HAS_ERT) &&
+	    (adapter->netdev->mtu > ETH_DATA_LEN))
 		hwm = min(((pba << 10) * 9 / 10),
 			  ((pba << 10) - (E1000_ERT_2048 << 3)));
 	else
 		hwm = min(((pba << 10) * 9 / 10),
-			  ((pba << 10) - adapter->max_frame_size));
+			  ((pba << 10) - (2 * adapter->max_frame_size)));
 
-	fc->high_water = hwm & 0xFFF8; /* 8-byte granularity */
-	fc->low_water = fc->high_water - 8;
+	fc->high_water = hwm & E1000_FCRTH_RTH; /* 8-byte granularity */
+	fc->low_water = (fc->high_water - (2 * adapter->max_frame_size));
+	fc->low_water &= E1000_FCRTL_RTL; /* 8-byte granularity */
 
 	if (adapter->flags & FLAG_DISABLE_FC_PAUSE_TIME)
 		fc->pause_time = 0xFFFF;