watchdog: imx7ulp: Add explict memory barrier for unlock sequence

When reconfiguring the WDOG Timer of i.MX7ULP, there is a certain
probability causes it to reset. The reason is that the CMD32EN of the
WDOG Timer of i.MX7ULP is disabled in bootloader. The unlock sequence
are two 16-bit writes to the CNT register within 16 bus clocks. Adding
mb() is to guarantee that two 16-bit writes are finished within 16 bus
clocks. Memory barriers cannot be added between these two 16-bit writes
so that writel_relaxed is used.

Suggested-by: Ye Li <[email protected]>
Signed-off-by: Jacky Bai <[email protected]>
Signed-off-by: Alice Guo <[email protected]>
Reviewed-by: Ye Li <[email protected]>
Reviewed-by: Guenter Roeck <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Wim Van Sebroeck <[email protected]>

Author: JackyBai

drivers/watchdog/imx7ulp_wdt.c

@@ -179,9 +179,13 @@ static int imx7ulp_wdt_init(void __iomem *base, unsigned int timeout)
 	int ret;
 
 	local_irq_disable();
+
+	mb();
 	/* unlock the wdog for reconfiguration */
 	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
 	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
+	mb();
+
 	ret = imx7ulp_wdt_wait(base, WDOG_CS_ULK);
 	if (ret)
 		goto init_out;