[PATCH] IMX: Rearm watchdog after loading value for restart

[frederikj at gmail.com]

When calling the restart function the watchdog is activated and the WDOG
timeout field is set to 0. This gives a reset time of 500 ms, which is
consistent with the following delay. However this new time is not loaded
into the WDOG until the WDOG service routine is run (see IMX6SXRM section
70.5.1.1 "Servicing WDOG to reload the counter").

Not reloading the counter could result in a random delay up to 128 seconds
before the system restarts, depending on the previous value of the WDOG
timeout field and when it has last been serviced. That bug is fixed with
this patch.

Signed-off-by: Frederik Juul <Frederik.juul at 3shape.com>

--- linux/arch/arm/mach-imx/system.c.orig	2017-04-20 10:41:33.207558297 +0200
+++ linux/arch/arm/mach-imx/system.c	2017-04-27 14:27:19.225474885 +0200
@@ -32,6 +32,8 @@
 #include "common.h"
 #include "hardware.h"
 
+#define IMX_WATCHDOG_SERVICE_REGISTER 2
+
 static void __iomem *wdog_base;
 static struct clk *wdog_clk;
 static int wcr_enable = (1 << 2);
@@ -59,6 +61,10 @@ void mxc_restart(enum reboot_mode mode,
 	imx_writew(wcr_enable, wdog_base);
 	imx_writew(wcr_enable, wdog_base);
 
+	/* Rearm WDOG to load 500ms value */
+	imx_writew(0x5555, wdog_base+IMX_WATCHDOG_SERVICE_REGISTER);
+	imx_writew(0xaaaa, wdog_base+IMX_WATCHDOG_SERVICE_REGISTER);
+
 	/* wait for reset to assert... */
 	mdelay(500);