[PATCH v6 4/4] watchdog: vt8500: Add a restart handler

[Alexey Charkov <alchark@gmail.com>]

Reset the SoC through the watchdog when the machine's own restart hook
leaves it running: the PMSR write in vt8500_restart() has no effect on
WM8950, so a reboot there ends in "Reboot failed -- System halted"
unless a watchdog armed from userspace happens to fire.

Arm the match a millisecond ahead of the current count, which leaves
ample margin for the register writes to land.

Register at priority 128, the default for restart handlers and also the
priority of the ARM machine restart hook. That hook is registered first,
from setup_arch(), and handlers of equal priority run in registration
order, so this one runs right after it and only matters where the hook
fails to reset the SoC.

Signed-off-by: Alexey Charkov <alchark@gmail.com>
---
 drivers/watchdog/vt8500-wdt.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/watchdog/vt8500-wdt.c b/drivers/watchdog/vt8500-wdt.c
index e0f838fd1d50..0ce1e2b06410 100644
--- a/drivers/watchdog/vt8500-wdt.c
+++ b/drivers/watchdog/vt8500-wdt.c
@@ -25,6 +25,9 @@
 
 #define VT8500_WDT_DEFAULT_TIMEOUT	30	/* seconds */
 
+/* How far ahead of the current count to arm the match for a restart */
+#define VT8500_WDT_RESTART_TICKS	(VT8500_TIMER_HZ / 1000)	/* 1 ms */
+
 static bool nowayout = WATCHDOG_NOWAYOUT;
 module_param(nowayout, bool, 0);
 MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
@@ -75,9 +78,18 @@ static int vt8500_watchdog_stop(struct watchdog_device *wdd)
 	return 0;
 }
 
+static int vt8500_watchdog_restart(struct watchdog_device *wdd,
+				   unsigned long action, void *data)
+{
+	struct vt8500_wdt_info *info = watchdog_get_drvdata(wdd);
+
+	return vt8500_watchdog_arm(info, VT8500_WDT_RESTART_TICKS);
+}
+
 static const struct watchdog_ops vt8500_watchdog_ops = {
 	.start			= vt8500_watchdog_start,
 	.stop			= vt8500_watchdog_stop,
+	.restart		= vt8500_watchdog_restart,
 };
 
 static const struct watchdog_info vt8500_watchdog_info = {
@@ -107,6 +119,7 @@ static int vt8500_wdt_probe(struct auxiliary_device *auxdev,
 	info = container_of(auxdev, struct vt8500_wdt_info, auxdev);
 	watchdog_set_drvdata(wdd, info);
 	watchdog_set_nowayout(wdd, nowayout);
+	watchdog_set_restart_priority(wdd, 128);
 
 	/* Let the core feed a watchdog left running, e.g. across kexec */
 	if (readl(info->regbase + VT8500_WDT_EN_REG) & VT8500_WDT_EN)

-- 
2.56.0