clocksource/drivers/imx-tpm: Fix next event not taking effect sometime

The value written into the TPM CnV can only be updated into the hardware
when the counter increases. Additional writes to the CnV write buffer are
ignored until the register has been updated. Therefore, we need to check
if the CnV has been updated before continuing. This may require waiting for
1 counter cycle in the worst case.

Cc: stable@vger.kernel.org
Fixes: 059ab7b ("clocksource/drivers/imx-tpm: Add imx tpm timer support")
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>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20240725193355.1436005-2-Frank.Li@nxp.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/timer-imx-tpm.c

@@ -90,6 +90,14 @@ static int tpm_set_next_event(unsigned long 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