nfp: eliminate an if statement in calculation of completed frames

Given that our rings are always a power of 2, we can simplify the
calculation of number of completed TX descriptors by using masking
instead of if statement based on whether the index have wrapped
or not.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Jakub Kicinski

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -940,10 +940,7 @@ static void nfp_net_tx_complete(struct nfp_net_tx_ring *tx_ring)
 	if (qcp_rd_p == tx_ring->qcp_rd_p)
 		return;
 
-	if (qcp_rd_p > tx_ring->qcp_rd_p)
-		todo = qcp_rd_p - tx_ring->qcp_rd_p;
-	else
-		todo = qcp_rd_p + tx_ring->cnt - tx_ring->qcp_rd_p;
+	todo = D_IDX(tx_ring, qcp_rd_p + tx_ring->cnt - tx_ring->qcp_rd_p);
 
 	while (todo--) {
 		idx = D_IDX(tx_ring, tx_ring->rd_p++);
@@ -1014,10 +1011,7 @@ static bool nfp_net_xdp_complete(struct nfp_net_tx_ring *tx_ring)
 	if (qcp_rd_p == tx_ring->qcp_rd_p)
 		return true;
 
-	if (qcp_rd_p > tx_ring->qcp_rd_p)
-		todo = qcp_rd_p - tx_ring->qcp_rd_p;
-	else
-		todo = qcp_rd_p + tx_ring->cnt - tx_ring->qcp_rd_p;
+	todo = D_IDX(tx_ring, qcp_rd_p + tx_ring->cnt - tx_ring->qcp_rd_p);
 
 	done_all = todo <= NFP_NET_XDP_MAX_COMPLETE;
 	todo = min(todo, NFP_NET_XDP_MAX_COMPLETE);