[PATCH] RTC: Implement pretimeout watchdog for DS1307

[Mark Tomlinson <mark.tomlinson@xxxxxxxxxxxxxxxxxxx>]

If the hardware watchdog in the clock chip simply pulls the reset line
of the CPU, then there is no chance to write a stack trace to help
determine what may have been blocking the CPU.

This patch adds a pretimeout to the watchdog, which, if enabled, sets
a timer to go off before the hardware watchdog kicks in, and calls
the standard pretimeout function, which can (for example) call panic.

Signed-off-by: Mark Tomlinson <mark.tomlinson@xxxxxxxxxxxxxxxxxxx>
---
 drivers/rtc/rtc-ds1307.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 49702942bb08..647f8659d0bd 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -23,6 +23,7 @@
 #include <linux/clk-provider.h>
 #include <linux/regmap.h>
 #include <linux/watchdog.h>
+#include <linux/timer.h>
 
 /*
  * We can't determine type by probing, but if we expect pre-Linux code
@@ -174,6 +175,10 @@ struct ds1307 {
 #ifdef CONFIG_COMMON_CLK
 	struct clk_hw		clks[2];
 #endif
+#ifdef CONFIG_WATCHDOG_CORE
+	struct timer_list	soft_timer;
+	struct watchdog_device	*wdt;
+#endif
 };
 
 struct chip_desc {
@@ -863,12 +868,34 @@ static int m41txx_rtc_set_offset(struct device *dev, long offset)
 }
 
 #ifdef CONFIG_WATCHDOG_CORE
+static void ds1388_soft_wdt_expire(struct timer_list *soft_timer)
+{
+	struct ds1307 *ds1307 = container_of(soft_timer, struct ds1307, soft_timer);
+
+	watchdog_notify_pretimeout(ds1307->wdt);
+}
+
+static void ds1388_soft_timer_set(struct watchdog_device *wdt_dev)
+{
+	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
+	int soft_timeout;
+
+	if (wdt_dev->pretimeout > 0) {
+		soft_timeout = wdt_dev->timeout - wdt_dev->pretimeout;
+		mod_timer(&ds1307->soft_timer, jiffies + soft_timeout * HZ);
+	} else {
+		del_timer(&ds1307->soft_timer);
+	}
+}
+
 static int ds1388_wdt_start(struct watchdog_device *wdt_dev)
 {
 	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
 	u8 regs[2];
 	int ret;
 
+	ds1388_soft_timer_set(wdt_dev);
+
 	ret = regmap_update_bits(ds1307->regmap, DS1388_REG_FLAG,
 				 DS1388_BIT_WF, 0);
 	if (ret)
@@ -900,6 +927,7 @@ static int ds1388_wdt_stop(struct watchdog_device *wdt_dev)
 {
 	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
 
+	del_timer(&ds1307->soft_timer);
 	return regmap_update_bits(ds1307->regmap, DS1388_REG_CONTROL,
 				  DS1388_BIT_WDE | DS1388_BIT_RST, 0);
 }
@@ -909,6 +937,7 @@ static int ds1388_wdt_ping(struct watchdog_device *wdt_dev)
 	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
 	u8 regs[2];
 
+	ds1388_soft_timer_set(wdt_dev);
 	return regmap_bulk_read(ds1307->regmap, DS1388_REG_WDOG_HUN_SECS, regs,
 				sizeof(regs));
 }
@@ -923,6 +952,7 @@ static int ds1388_wdt_set_timeout(struct watchdog_device *wdt_dev,
 	regs[0] = 0;
 	regs[1] = bin2bcd(wdt_dev->timeout);
 
+	ds1388_soft_timer_set(wdt_dev);
 	return regmap_bulk_write(ds1307->regmap, DS1388_REG_WDOG_HUN_SECS, regs,
 				 sizeof(regs));
 }
@@ -1652,7 +1682,8 @@ static void ds1307_clks_register(struct ds1307 *ds1307)
 
 #ifdef CONFIG_WATCHDOG_CORE
 static const struct watchdog_info ds1388_wdt_info = {
-	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
+	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
+		   WDIOF_MAGICCLOSE | WDIOF_PRETIMEOUT,
 	.identity = "DS1388 watchdog",
 };
 
@@ -1681,6 +1712,8 @@ static void ds1307_wdt_register(struct ds1307 *ds1307)
 	wdt->timeout = 99;
 	wdt->max_timeout = 99;
 	wdt->min_timeout = 1;
+	ds1307->wdt = wdt;
+	timer_setup(&ds1307->soft_timer, ds1388_soft_wdt_expire, 0);
 
 	watchdog_init_timeout(wdt, 0, ds1307->dev);
 	watchdog_set_drvdata(wdt, ds1307);
-- 
2.28.0