LF-9952 clocksource: imx-tpm: Wait for CnV write to take effect

The value write into the TPM CnV can only be updated into the HW when
CNT increase. Additional writes to the CnV write buffer are ignored until
the register has been updated. So we need to check if the CnV has been
updated before continue. Wait for 1 CNT cycle in worst case.

Additionally, current return check is not correct, if a max_delta need
be set, it will return '-ETIME' wrongly due to the 'int' type cast,
so refine the check logic to fix it.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Jason Liu <jason.hui.liu@nxp.com>

Author: JackyBai

drivers/clocksource/timer-imx-tpm.c

@@ -83,20 +83,28 @@ static u64 notrace tpm_read_sched_clock(void)
 static int tpm_set_next_event(unsigned long delta,
 				struct clock_event_device *evt)
 {
-	unsigned long next, now;
+	unsigned long next, prev, now;
 
-	next = tpm_read_counter();
-	next += delta;
+	prev = tpm_read_counter();
+	next = prev + delta;
 	writel(next, timer_base + TPM_C0V);
 	now = tpm_read_counter();
 
+	/*
+	 * Need to wait CNT increase at least 1 cycle to make sure
+	 * the C0V has been updated into HW.
+	 */
+	if ((next & 0xffffffff) != readl(timer_base + TPM_C0V))
+		while (now == tpm_read_counter())
+			;
+
 	/*
 	 * NOTE: We observed in a very small probability, the bus fabric
 	 * contention between GPU and A7 may results a few cycles delay
 	 * of writing CNT registers which may cause the min_delta event got
 	 * missed, so we need add a ETIME check here in case it happened.
 	 */
-	return (int)(next - now) <= 0 ? -ETIME : 0;
+	return (now - prev) >= delta ? -ETIME : 0;
 }
 
 static int tpm_set_state_oneshot(struct clock_event_device *evt)