ixgbe: DCB, fix TX hang occurring in stress condition with PFC

The DCB credits refill quantum _must_ be greater than half the max
packet size. This is needed to guarantee that TX DMA operations
are not attempted during a pause state. Additionally, the min IFG
must be set correctly for DCB mode. If a DMA operation is
requested unexpectedly during the pause state the HW data
store may be corrupted leading to a DMA hang. The DMA hang
requires a reset to correct. This fixes the HW configuration
to avoid this condition.

Signed-off-by: John Fastabend <[e-mail]>
Tested-by: Ross Brattain <[e-mail]>
Signed-off-by: Jeff Kirsher <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ixgbe/ixgbe_dcb.c

···
  * ixgbe_dcb_check_config().
  */
 s32 ixgbe_dcb_calculate_tc_credits(struct ixgbe_dcb_config *dcb_config,
-                                   u8 direction)
+				   int max_frame, u8 direction)
 {
 	struct tc_bw_alloc *p;
+	int min_credit;
+	int min_multiplier;
+	int min_percent = 100;
 	s32 ret_val = 0;
 	/* Initialization values default for Tx settings */
 	u32 credit_refill       = 0;
···
 		ret_val = DCB_ERR_CONFIG;
 		goto out;
 	}
+
+	min_credit = ((max_frame / 2) + DCB_CREDIT_QUANTUM - 1) /
+			DCB_CREDIT_QUANTUM;
+
+	/* Find smallest link percentage */
+	for (i = 0; i < MAX_TRAFFIC_CLASS; i++) {
+		p = &dcb_config->tc_config[i].path[direction];
+		bw_percent = dcb_config->bw_percentage[direction][p->bwg_id];
+		link_percentage = p->bwg_percent;
+
+		link_percentage = (link_percentage * bw_percent) / 100;
+
+		if (link_percentage && link_percentage < min_percent)
+			min_percent = link_percentage;
+	}
+
+	/*
+	 * The ratio between traffic classes will control the bandwidth
+	 * percentages seen on the wire. To calculate this ratio we use
+	 * a multiplier. It is required that the refill credits must be
+	 * larger than the max frame size so here we find the smallest
+	 * multiplier that will allow all bandwidth percentages to be
+	 * greater than the max frame size.
+	 */
+	min_multiplier = (min_credit / min_percent) + 1;
 
 	/* Find out the link percentage for each TC first */
 	for (i = 0; i < MAX_TRAFFIC_CLASS; i++) {
···
 		/* Save link_percentage for reference */
 		p->link_percent = (u8)link_percentage;
 
-		/* Calculate credit refill and save it */
-		credit_refill = link_percentage * MINIMUM_CREDIT_REFILL;
+		/* Calculate credit refill ratio using multiplier */
+		credit_refill = min(link_percentage * min_multiplier,
+				    MAX_CREDIT_REFILL);
 		p->data_credits_refill = (u16)credit_refill;
 
 		/* Calculate maximum credit for the TC */
···
 		 * of a TC is too small, the maximum credit may not be
 		 * enough to send out a jumbo frame in data plane arbitration.
 		 */
-		if (credit_max && (credit_max < MINIMUM_CREDIT_FOR_JUMBO))
-			credit_max = MINIMUM_CREDIT_FOR_JUMBO;
+		if (credit_max && (credit_max < min_credit))
+			credit_max = min_credit;
 
 		if (direction == DCB_TX_CONFIG) {
 			/*

drivers/net/ixgbe/ixgbe_dcb.h

···
 /* DCB driver APIs */
 
 /* DCB credits calculation */
-s32 ixgbe_dcb_calculate_tc_credits(struct ixgbe_dcb_config *, u8);
+s32 ixgbe_dcb_calculate_tc_credits(struct ixgbe_dcb_config *, int, u8);
 
 /* DCB hw initialization */
 s32 ixgbe_dcb_hw_config(struct ixgbe_hw *, struct ixgbe_dcb_config *);
 
 /* DCB definitions for credit calculation */
+#define DCB_CREDIT_QUANTUM	64   /* DCB Quantum */
 #define MAX_CREDIT_REFILL       511  /* 0x1FF * 64B = 32704B */
-#define MINIMUM_CREDIT_REFILL   5    /* 5*64B = 320B */
-#define MINIMUM_CREDIT_FOR_JUMBO 145  /* 145= UpperBound((9*1024+54)/64B) for 9KB jumbo frame */
 #define DCB_MAX_TSO_SIZE        (32*1024) /* MAX TSO packet size supported in DCB mode */
 #define MINIMUM_CREDIT_FOR_TSO  (DCB_MAX_TSO_SIZE/64 + 1) /* 513 for 32KB TSO packet */
 #define MAX_CREDIT              4095 /* Maximum credit supported: 256KB * 1204 / 64B */

drivers/net/ixgbe/ixgbe_dcb_82599.c

···
 	reg &= ~IXGBE_RTTDCS_ARBDIS;
 	IXGBE_WRITE_REG(hw, IXGBE_RTTDCS, reg);
 
+	/* Enable Security TX Buffer IFG for DCB */
+	reg = IXGBE_READ_REG(hw, IXGBE_SECTXMINIFG);
+	reg |= IXGBE_SECTX_DCB;
+	IXGBE_WRITE_REG(hw, IXGBE_SECTXMINIFG, reg);
+
 	return 0;
 }
 

drivers/net/ixgbe/ixgbe_dcb_82599.h

···
 
 #define IXGBE_TXPBTHRESH_DCB    0xA        /* THRESH value for DCB mode */
 
+/* SECTXMINIFG DCB */
+#define IXGBE_SECTX_DCB		0x00001F00 /* DCB TX Buffer IFG */
+
 
 /* DCB hardware-specific driver APIs */
 

drivers/net/ixgbe/ixgbe_main.c

···
 static void ixgbe_configure_dcb(struct ixgbe_adapter *adapter)
 {
 	struct ixgbe_hw *hw = &adapter->hw;
+	int max_frame = adapter->netdev->mtu + ETH_HLEN + ETH_FCS_LEN;
 	u32 txdctl;
 	int i, j;
 
···
 	if (hw->mac.type == ixgbe_mac_82598EB)
 		netif_set_gso_max_size(adapter->netdev, 32768);
 
-	ixgbe_dcb_calculate_tc_credits(&adapter->dcb_cfg, DCB_TX_CONFIG);
-	ixgbe_dcb_calculate_tc_credits(&adapter->dcb_cfg, DCB_RX_CONFIG);
+#ifdef CONFIG_FCOE
+	if (adapter->netdev->features & NETIF_F_FCOE_MTU)
+		max_frame = max(max_frame, IXGBE_FCOE_JUMBO_FRAME_SIZE);
+#endif
+
+	ixgbe_dcb_calculate_tc_credits(&adapter->dcb_cfg, max_frame,
+					DCB_TX_CONFIG);
+	ixgbe_dcb_calculate_tc_credits(&adapter->dcb_cfg, max_frame,
+					DCB_RX_CONFIG);
 
 	/* reconfigure the hardware */
 	ixgbe_dcb_hw_config(&adapter->hw, &adapter->dcb_cfg);