net: ethernet: ti: am65-cpsw-qos: Add support to taprio for past base_time

If the base-time for taprio is in the past, start the schedule at the time
of the form "base_time + N*cycle_time" where N is the smallest possible
integer such that the above time is in the future.
Signed-off-by: Tanmay Patil <t-patil@ti.com>
Signed-off-by: Chintan Vankar <c-vankar@ti.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/am65-cpsw-qos.c

@@ -9,6 +9,7 @@
 
 #include <linux/pm_runtime.h>
 #include <linux/math.h>
+#include <linux/math64.h>
 #include <linux/time.h>
 #include <linux/units.h>
 #include <net/pkt_cls.h>
@@ -837,6 +838,7 @@ static int am65_cpsw_taprio_replace(struct net_device *ndev,
 	struct am65_cpsw_port *port = am65_ndev_to_port(ndev);
 	struct am65_cpts *cpts = common->cpts;
 	struct am65_cpsw_est *est_new;
+	u64 cur_time, n;
 	int ret, tact;
 
 	if (!netif_running(ndev)) {
@@ -888,13 +890,21 @@ static int am65_cpsw_taprio_replace(struct net_device *ndev,
 	if (tact == TACT_PROG)
 		am65_cpsw_timer_stop(ndev);
 
-	if (!est_new->taprio.base_time)
-		est_new->taprio.base_time = am65_cpts_ns_gettime(cpts);
-
 	am65_cpsw_port_est_get_buf_num(ndev, est_new);
 	am65_cpsw_est_set_sched_list(ndev, est_new);
 	am65_cpsw_port_est_assign_buf_num(ndev, est_new->buf);
 
+	/* If the base-time is in the past, start schedule from the time:
+	 * base_time + (N*cycle_time)
+	 * where N is the smallest possible integer such that the above
+	 * time is in the future.
+	 */
+	cur_time = am65_cpts_ns_gettime(cpts);
+	if (est_new->taprio.base_time < cur_time) {
+		n = div64_u64(cur_time - est_new->taprio.base_time, est_new->taprio.cycle_time);
+		est_new->taprio.base_time += (n + 1) * est_new->taprio.cycle_time;
+	}
+
 	am65_cpsw_est_set(ndev, 1);
 
 	if (tact == TACT_PROG) {