ixgbe: update {P}FC thresholds to account for X540 and loopback

Revise high and low threshold marks wrt flow control to account
for the X540 devices and latency introduced by the loopback
switch.

Without this it was in theory possible to drop frames on a
supposedly lossless link with X540 or SR-IOV enabled.

Previously we used a magic number in a define to calculate the
threshold values. This made it difficult to sort out exactly
which latencies were or were not being accounted for. Here
I was overly explicit and tried to used #define names that would
be recognizable after reading the IEEE 802.1Qbb specification.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 121 insertions, 7 deletions

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 3594b09f4993..ba703d30f3a9 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -3351,9 +3351,128 @@ static void ixgbe_configure_dcb(struct ixgbe_adapter *adapter)
 		IXGBE_WRITE_REG(hw, IXGBE_RQTC, reg);
 	}
 }
+#endif
+
+/* Additional bittime to account for IXGBE framing */
+#define IXGBE_ETH_FRAMING 20
+
+/*
+ * ixgbe_hpbthresh - calculate high water mark for flow control
+ *
+ * @adapter: board private structure to calculate for
+ * @pb - packet buffer to calculate
+ */
+static int ixgbe_hpbthresh(struct ixgbe_adapter *adapter, int pb)
+{
+	struct ixgbe_hw *hw = &adapter->hw;
+	struct net_device *dev = adapter->netdev;
+	int link, tc, kb, marker;
+	u32 dv_id, rx_pba;
+
+	/* Calculate max LAN frame size */
+	tc = link = dev->mtu + ETH_HLEN + ETH_FCS_LEN + IXGBE_ETH_FRAMING;
+
+#ifdef IXGBE_FCOE
+	/* FCoE traffic class uses FCOE jumbo frames */
+	if (dev->features & NETIF_F_FCOE_MTU) {
+		int fcoe_pb = 0;
 
+#ifdef CONFIG_IXGBE_DCB
+		fcoe_pb = netdev_get_prio_tc_map(dev, adapter->fcoe.up);
+
+#endif
+		if (fcoe_pb == pb && tc < IXGBE_FCOE_JUMBO_FRAME_SIZE)
+			tc = IXGBE_FCOE_JUMBO_FRAME_SIZE;
+	}
 #endif
 
+	/* Calculate delay value for device */
+	switch (hw->mac.type) {
+	case ixgbe_mac_X540:
+		dv_id = IXGBE_DV_X540(link, tc);
+		break;
+	default:
+		dv_id = IXGBE_DV(link, tc);
+		break;
+	}
+
+	/* Loopback switch introduces additional latency */
+	if (adapter->flags & IXGBE_FLAG_SRIOV_ENABLED)
+		dv_id += IXGBE_B2BT(tc);
+
+	/* Delay value is calculated in bit times convert to KB */
+	kb = IXGBE_BT2KB(dv_id);
+	rx_pba = IXGBE_READ_REG(hw, IXGBE_RXPBSIZE(pb)) >> 10;
+
+	marker = rx_pba - kb;
+
+	/* It is possible that the packet buffer is not large enough
+	 * to provide required headroom. In this case throw an error
+	 * to user and a do the best we can.
+	 */
+	if (marker < 0) {
+		e_warn(drv, "Packet Buffer(%i) can not provide enough"
+			    "headroom to support flow control."
+			    "Decrease MTU or number of traffic classes\n", pb);
+		marker = tc + 1;
+	}
+
+	return marker;
+}
+
+/*
+ * ixgbe_lpbthresh - calculate low water mark for for flow control
+ *
+ * @adapter: board private structure to calculate for
+ * @pb - packet buffer to calculate
+ */
+static int ixgbe_lpbthresh(struct ixgbe_adapter *adapter)
+{
+	struct ixgbe_hw *hw = &adapter->hw;
+	struct net_device *dev = adapter->netdev;
+	int tc;
+	u32 dv_id;
+
+	/* Calculate max LAN frame size */
+	tc = dev->mtu + ETH_HLEN + ETH_FCS_LEN;
+
+	/* Calculate delay value for device */
+	switch (hw->mac.type) {
+	case ixgbe_mac_X540:
+		dv_id = IXGBE_LOW_DV_X540(tc);
+		break;
+	default:
+		dv_id = IXGBE_LOW_DV(tc);
+		break;
+	}
+
+	/* Delay value is calculated in bit times convert to KB */
+	return IXGBE_BT2KB(dv_id);
+}
+
+/*
+ * ixgbe_pbthresh_setup - calculate and setup high low water marks
+ */
+static void ixgbe_pbthresh_setup(struct ixgbe_adapter *adapter)
+{
+	struct ixgbe_hw *hw = &adapter->hw;
+	int num_tc = netdev_get_num_tc(adapter->netdev);
+	int i;
+
+	if (!num_tc)
+		num_tc = 1;
+
+	hw->fc.low_water = ixgbe_lpbthresh(adapter);
+
+	for (i = 0; i < num_tc; i++) {
+		hw->fc.high_water[i] = ixgbe_hpbthresh(adapter, i);
+
+		/* Low water marks must not be larger than high water marks */
+		if (hw->fc.low_water > hw->fc.high_water[i])
+			hw->fc.low_water = 0;
+	}
+}
+
 static void ixgbe_configure_pb(struct ixgbe_adapter *adapter)
 {
 	struct ixgbe_hw *hw = &adapter->hw;
@@ -3367,6 +3486,7 @@ static void ixgbe_configure_pb(struct ixgbe_adapter *adapter)
 		hdrm = 0;
 
 	hw->mac.ops.set_rxpba(hw, tc, hdrm, PBA_STRATEGY_EQUAL);
+	ixgbe_pbthresh_setup(adapter);
 }
 
 static void ixgbe_fdir_filter_restore(struct ixgbe_adapter *adapter)
@@ -4769,13 +4889,11 @@ static int __devinit ixgbe_sw_init(struct ixgbe_adapter *adapter)
 {
 	struct ixgbe_hw *hw = &adapter->hw;
 	struct pci_dev *pdev = adapter->pdev;
-	struct net_device *dev = adapter->netdev;
 	unsigned int rss;
 #ifdef CONFIG_IXGBE_DCB
 	int j;
 	struct tc_configuration *tc;
 #endif
-	int max_frame = dev->mtu + ETH_HLEN + ETH_FCS_LEN;
 
 	/* PCI config space info */
 
@@ -4851,8 +4969,7 @@ static int __devinit ixgbe_sw_init(struct ixgbe_adapter *adapter)
 #ifdef CONFIG_DCB
 	adapter->last_lfc_mode = hw->fc.current_mode;
 #endif
-	hw->fc.high_water = FC_HIGH_WATER(max_frame);
-	hw->fc.low_water = FC_LOW_WATER(max_frame);
+	ixgbe_pbthresh_setup(adapter);
 	hw->fc.pause_time = IXGBE_DEFAULT_FCPAUSE;
 	hw->fc.send_xon = true;
 	hw->fc.disable_fc_autoneg = false;
@@ -5119,9 +5236,6 @@ static int ixgbe_change_mtu(struct net_device *netdev, int new_mtu)
 	/* must set new MTU before calling down or up */
 	netdev->mtu = new_mtu;
 
-	hw->fc.high_water = FC_HIGH_WATER(max_frame);
-	hw->fc.low_water = FC_LOW_WATER(max_frame);
-
 	if (netif_running(netdev))
 		ixgbe_reinit_locked(adapter);