watchdog: at91sam9_wdt: increase security margin on watchdog counter reset

Try to reset the watchdog counter 4 or 2 times more often than actually
requested, to avoid spurious watchdog reset.
If this is not possible because of the min_heartbeat value, reset it at
the min_heartbeat period.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
index ab0c4e0..489729b 100644 (file)
--- a/drivers/watchdog/at91sam9_wdt.c
+++ b/drivers/watchdog/at91sam9_wdt.c
@@ -158,6 +158,7 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
        int err;
        u32 mask = wdt->mr_mask;
        unsigned long min_heartbeat = 1;
+       unsigned long max_heartbeat;
        struct device *dev = &pdev->dev;
 
        tmp = wdt_read(wdt, AT91_WDT_MR);
@@ -181,23 +182,29 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
        if (delta < value)
                min_heartbeat = ticks_to_hz_roundup(value - delta);
 
-       wdt->heartbeat = ticks_to_hz_rounddown(value);
-       if (!wdt->heartbeat) {
+       max_heartbeat = ticks_to_hz_rounddown(value);
+       if (!max_heartbeat) {
                dev_err(dev,
                        "heartbeat is too small for the system to handle it correctly\n");
                return -EINVAL;
        }
 
-       if (wdt->heartbeat < min_heartbeat + 4) {
+       /*
+        * Try to reset the watchdog counter 4 or 2 times more often than
+        * actually requested, to avoid spurious watchdog reset.
+        * If this is not possible because of the min_heartbeat value, reset
+        * it at the min_heartbeat period.
+        */
+       if ((max_heartbeat / 4) >= min_heartbeat)
+               wdt->heartbeat = max_heartbeat / 4;
+       else if ((max_heartbeat / 2) >= min_heartbeat)
+               wdt->heartbeat = max_heartbeat / 2;
+       else
                wdt->heartbeat = min_heartbeat;
+
+       if (max_heartbeat < min_heartbeat + 4)
                dev_warn(dev,
                         "min heartbeat and max heartbeat might be too close for the system to handle it correctly\n");
-               if (wdt->heartbeat < 4)
-                       dev_warn(dev,
-                                "heartbeat might be too small for the system to handle it correctly\n");
-       } else {
-               wdt->heartbeat -= 4;
-       }
 
        if ((tmp & AT91_WDT_WDFIEN) && wdt->irq) {
                err = request_irq(wdt->irq, wdt_interrupt,