bnxt_en: Fix completion ring sizing with TPA enabled.

The current completion ring sizing formula is wrong with TPA enabled.
The formula assumes that the number of TPA completions are bound by the
RX ring size, but that's not true.  TPA_START completions are immediately
recycled so they are not bound by the RX ring size.  We must add
bp->max_tpa to the worst case maximum RX and TPA completions.

The completion ring can overflow because of this mistake.  This will
cause hardware to disable the completion ring when this happens,
leading to RX and TX traffic to stall on that ring.  This issue is
generally exposed only when the RX ring size is set very small.

Fix the formula by adding bp->max_tpa to the number of RX completions
if TPA is enabled.

Fixes: c0c050c5 ("bnxt_en: New Broadcom ethernet driver.");
Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -3418,7 +3418,7 @@ void bnxt_set_tpa_flags(struct bnxt *bp)
  */
 void bnxt_set_ring_params(struct bnxt *bp)
 {
-	u32 ring_size, rx_size, rx_space;
+	u32 ring_size, rx_size, rx_space, max_rx_cmpl;
 	u32 agg_factor = 0, agg_ring_size = 0;
 
 	/* 8 for CRC and VLAN */
@@ -3474,7 +3474,15 @@ void bnxt_set_ring_params(struct bnxt *bp)
 	bp->tx_nr_pages = bnxt_calc_nr_ring_pages(ring_size, TX_DESC_CNT);
 	bp->tx_ring_mask = (bp->tx_nr_pages * TX_DESC_CNT) - 1;
 
-	ring_size = bp->rx_ring_size * (2 + agg_factor) + bp->tx_ring_size;
+	max_rx_cmpl = bp->rx_ring_size;
+	/* MAX TPA needs to be added because TPA_START completions are
+	 * immediately recycled, so the TPA completions are not bound by
+	 * the RX ring size.
+	 */
+	if (bp->flags & BNXT_FLAG_TPA)
+		max_rx_cmpl += bp->max_tpa;
+	/* RX and TPA completions are 32-byte, all others are 16-byte */
+	ring_size = max_rx_cmpl * 2 + agg_ring_size + bp->tx_ring_size;
 	bp->cp_ring_size = ring_size;
 
 	bp->cp_nr_pages = bnxt_calc_nr_ring_pages(ring_size, CP_DESC_CNT);