Currently we have no means to adjust the watchdog behavior on early start up before user space has opened the device. The generic behavior among the watchdog drivers is to not start the watchdog at all (or disable it, if possible, or in case at91sam9_wdt, start a kernel timer that keeps on pinging the watchdog on behalf of user space until a watchdog daemon opens it). This unfortunately opens a time window between starting the driver and starting the user space watchdog daemon where a crash in the kernel or user space might prevent the watchdog from ever resetting the device at all. This is obviously bad on production systems. Introduce a new device tree property that, when set, changes the watchdog driver behavior in such way that there no longer is any window where crash is not caught by the watchdog. In atmel HW we need to use a kernel timer to ping the watchdog for the duration of the timeout, but that is trivial as we already have a timer there that keeps pinging it until the watchdog device is open. The documentation however only states how the driver should behave, not how it should be implemented in some other watchdog hardware. Patch revision history: -v4: Binding documentation is now separated completely from the driver patch. The documentation no longer makes any assumptions about how the actual implementation is made, it just describes the actual behavior the driver should implement in order to satisfy the requirement. - v3: Rename the property to "early-timeout-sec" and use it as a timeout value that stops the timer in the atmel driver after the timeout expires. A watchdog.txt is also introduced for documenting the common watchdog properties, including now this one and "timeout-sec" property. - v2: Rename the property to "enable-early-reset" as the behavior itself is not atmel specific. This way other drivers are free to implement same behavior with the same property name. - v1: Propose property name "atmle,no-early-timer" for disabling the timer that keeps the atmel watchdog running until user space opens the device. Timo Kokkonen (2): at91sam9_wdt: Allow watchdog to reset device at early boot devicetree: Document generic watchdog properties .../devicetree/bindings/watchdog/watchdog.txt | 20 ++++++++++++++++++++ drivers/watchdog/at91sam9_wdt.c | 9 ++++++++- 2 files changed, 28 insertions(+), 1 deletion(-) create mode 100644 Documentation/devicetree/bindings/watchdog/watchdog.txt -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
