[PATCH 4.17 018/101] net: macb: Fix ptp time adjustment for large negative delta

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Harini Katakam <harini.kata...@xilinx.com>

[ Upstream commit 64d7839af8c8f67daaf9bf387135052c55d85f90 ]

When delta passed to gem_ptp_adjtime is negative, the sign is
maintained in the ns_to_timespec64 conversion. Hence timespec_add
should be used directly. timespec_sub will just subtract the negative
value thus increasing the time difference.

Signed-off-by: Harini Katakam <harini.kata...@xilinx.com>
Acked-by: Nicolas Ferre <nicolas.fe...@microchip.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/net/ethernet/cadence/macb_ptp.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

--- a/drivers/net/ethernet/cadence/macb_ptp.c
+++ b/drivers/net/ethernet/cadence/macb_ptp.c
@@ -170,10 +170,7 @@ static int gem_ptp_adjtime(struct ptp_cl
 
        if (delta > TSU_NSEC_MAX_VAL) {
                gem_tsu_get_time(&bp->ptp_clock_info, &now);
-               if (sign)
-                       now = timespec64_sub(now, then);
-               else
-                       now = timespec64_add(now, then);
+               now = timespec64_add(now, then);
 
                gem_tsu_set_time(&bp->ptp_clock_info,
                                 (const struct timespec64 *)&now);