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Subject[PATCH] watchdog: at91sam9_wdt: various fixes
Date
Fix the secs_to_ticks macro in case 0 is passed as an argument.

Rework the heartbeat calculation to increase the security margin of the
watchdog reset timer.

Use the min_heartbeat value instead of the calculated heartbeat value for
the first watchdog reset.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
---
drivers/watchdog/at91sam9_wdt.c | 35 ++++++++++++++++++++++++-----------
1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
index 9bd089e..f1b59f1 100644
--- a/drivers/watchdog/at91sam9_wdt.c
+++ b/drivers/watchdog/at91sam9_wdt.c
@@ -51,7 +51,7 @@
#define ticks_to_hz_rounddown(t) ((((t) + 1) * HZ) >> 8)
#define ticks_to_hz_roundup(t) (((((t) + 1) * HZ) + 255) >> 8)
#define ticks_to_secs(t) (((t) + 1) >> 8)
-#define secs_to_ticks(s) (((s) << 8) - 1)
+#define secs_to_ticks(s) (s ? (((s) << 8) - 1) : 0)

#define WDT_MR_RESET 0x3FFF2FFF

@@ -61,6 +61,11 @@
/* Watchdog max delta/value in secs */
#define WDT_COUNTER_MAX_SECS ticks_to_secs(WDT_COUNTER_MAX_TICKS)

+/* Watchdog heartbeat shift used for security margin:
+ * we'll try to rshift the heartbeat value with this value to secure
+ * the watchdog reset. */
+#define WDT_HEARTBEAT_SHIFT 2
+
/* Hardware timeout in seconds */
#define WDT_HW_TIMEOUT 2

@@ -158,7 +163,9 @@ 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;
+ int shift;

tmp = wdt_read(wdt, AT91_WDT_MR);
if ((tmp & mask) != (wdt->mr & mask)) {
@@ -181,23 +188,27 @@ 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) {
+ for (shift = WDT_HEARTBEAT_SHIFT; shift > 0; shift--) {
+ if ((max_heartbeat >> shift) < min_heartbeat)
+ continue;
+
+ wdt->heartbeat = max_heartbeat >> shift;
+ break;
+ }
+
+ if (!shift)
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,
@@ -213,7 +224,9 @@ static int at91_wdt_init(struct platform_device *pdev, struct at91wdt *wdt)
tmp & wdt->mr_mask, wdt->mr & wdt->mr_mask);

setup_timer(&wdt->timer, at91_ping, (unsigned long)wdt);
- mod_timer(&wdt->timer, jiffies + wdt->heartbeat);
+ /* Use min_heartbeat the first time because the watchdog timer might
+ * be running for a long time when we reach this init function. */
+ mod_timer(&wdt->timer, jiffies + min_heartbeat);

/* Try to set timeout from device tree first */
if (watchdog_init_timeout(&wdt->wdd, 0, dev))
--
1.7.9.5


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