ptp: ocp: have adjtime handle negative delta_ns correctly

delta_ns is a s64, but it was being passed ptp_ocp_adjtime_coarse
as an u64.  Also, it turns out that timespec64_add_ns() only handles
positive values, so perform the math with set_normalized_timespec().

Fixes: 90f8f4c0 ("ptp: ocp: Add ptp_ocp_adjtime_coarse for large adjustments")
Suggested-by: Vadim Fedorenko <vfedorenko@novek.ru>
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Acked-by: Vadim Fedorenko <vfedorenko@novek.ru>
Link: https://lore.kernel.org/r/20220513225231.1412-1-jonathan.lemon@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/ptp/ptp_ocp.c

@@ -841,7 +841,7 @@ __ptp_ocp_adjtime_locked(struct ptp_ocp *bp, u32 adj_val)
 }
 
 static void
-ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, u64 delta_ns)
+ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, s64 delta_ns)
 {
 	struct timespec64 ts;
 	unsigned long flags;
@@ -850,7 +850,8 @@ ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, u64 delta_ns)
 	spin_lock_irqsave(&bp->lock, flags);
 	err = __ptp_ocp_gettime_locked(bp, &ts, NULL);
 	if (likely(!err)) {
-		timespec64_add_ns(&ts, delta_ns);
+		set_normalized_timespec64(&ts, ts.tv_sec,
+					  ts.tv_nsec + delta_ns);
 		__ptp_ocp_settime_locked(bp, &ts);
 	}
 	spin_unlock_irqrestore(&bp->lock, flags);