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Subject[PATCH 3/3] watchdog: at91sam9_wdt: increase security margin on watchdog counter reset
Date
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>
---
drivers/watchdog/at91sam9_wdt.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
index ab0c4e0..489729b 100644
--- 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,
--
1.7.9.5


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