clocksource/drivers/imx-tpm: Correct some registers operation flow

According to i.MX7ULP reference manual, TPM_SC_CPWMS can ONLY be written when
counter is disabled, TPM_SC_TOF is write-1-clear, TPM_C0SC_CHF is also
write-1-clear, correct these registers initialization flow;

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/timer-imx-tpm.c

@@ -20,6 +20,7 @@
 #define TPM_SC				0x10
 #define TPM_SC_CMOD_INC_PER_CNT		(0x1 << 3)
 #define TPM_SC_CMOD_DIV_DEFAULT		0x3
+#define TPM_SC_TOF_MASK			(0x1 << 7)
 #define TPM_CNT				0x14
 #define TPM_MOD				0x18
 #define TPM_STATUS			0x1c
@@ -29,6 +30,7 @@
 #define TPM_C0SC_MODE_SHIFT		2
 #define TPM_C0SC_MODE_MASK		0x3c
 #define TPM_C0SC_MODE_SW_COMPARE	0x4
+#define TPM_C0SC_CHF_MASK		(0x1 << 7)
 #define TPM_C0V				0x24
 
 static void __iomem *timer_base;
@@ -205,9 +207,13 @@ static int __init tpm_timer_init(struct device_node *np)
 	 * 4) Channel0 disabled
 	 * 5) DMA transfers disabled
 	 */
+	/* make sure counter is disabled */
 	writel(0, timer_base + TPM_SC);
+	/* TOF is W1C */
+	writel(TPM_SC_TOF_MASK, timer_base + TPM_SC);
 	writel(0, timer_base + TPM_CNT);
-	writel(0, timer_base + TPM_C0SC);
+	/* CHF is W1C */
+	writel(TPM_C0SC_CHF_MASK, timer_base + TPM_C0SC);
 
 	/* increase per cnt, div 8 by default */
 	writel(TPM_SC_CMOD_INC_PER_CNT | TPM_SC_CMOD_DIV_DEFAULT,