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 <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 5 deletions

diff --git a/drivers/net/ixgbe/ixgbe_dcb.c b/drivers/net/ixgbe/ixgbe_dcb.c
index 8bb9ddb6dffe..0d44c6470ca3 100644
--- a/drivers/net/ixgbe/ixgbe_dcb.c
+++ b/drivers/net/ixgbe/ixgbe_dcb.c
@@ -43,9 +43,12 @@
  * 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;
@@ -59,6 +62,31 @@ s32 ixgbe_dcb_calculate_tc_credits(struct ixgbe_dcb_config *dcb_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++) {
                 p = &dcb_config->tc_config[i].path[direction];
@@ -73,8 +101,9 @@ s32 ixgbe_dcb_calculate_tc_credits(struct ixgbe_dcb_config *dcb_config,
                 /* 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 */
@@ -85,8 +114,8 @@ s32 ixgbe_dcb_calculate_tc_credits(struct ixgbe_dcb_config *dcb_config,
                  * 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) {
                         /*