On 2015/4/10 21:06, Timo Kokkonen wrote:
The watchdog kernel API is quite limited. It has support for providing generic device handling, but it doesn't really know anything about the watchdog hardware or its constraints. The watchdog drivers come with a lot of diversity and their own set of quirks and constraints. Some of their limitations are not nice for the user space, so the drivers work around them with all sorts of ad hoc implementations. One common pattern is to use kernel timers or work queues to allow longer timeout parameters than the actual hardware supports. To solve this problem, this patch set extends the kernel watchdog API with a few parameters that let the core know more about the watchdog HW and take care about the timeout extending. The patch set also implements "early_timeout_sec" feature that is very common on many production systems where early kernel or user space crashes must lead to a device reset. Traditional watchdog handling does not allow this as the watchdog is stopped (fully or emulating stopped state with kernel timers) before user space opens it for the first time. The changes are designed to be taken in use one driver at time. If the driver does not set the new parameters and call watchdog_init_params(), the watchdog behavior is exactly the same as before. In principle this new API makes it possible for the user space to see every watchdog hardware to behave the same, at least in terms of watchdog timeouts. Once the API is in, it should be easier to move even more common behavior out of the driver code to the watchdog core and make the drivers simpler. I'm not anticipating this patch set to go in as is, this is merely to help bringing up the discussion as there is a working patch set to look at. There are propably some corner cases that I didn't get right yet. Also, we could even remove the maximum timeout completely as the HW no longer limits the watchdog timeouts. This propably needs some thinking still and your commenting. Please review and give feedback.
Tested on the SAMA5D4EK. Tested-by Wenyou Yang <wenyou.yang@xxxxxxxxx>
Patch revision history: -v5: Re-think the approach to be fully generic. The early_timeout_sec handling is no longer in the driver but in the watchdog core. As a result the core needed to gain knowledge about the watchdog hardware. Appropriate handling is added in the core. The side effect for this is that drivers using the new extensions can be simplified a lot and different kinds of watchdog hardware can be made to behave the same for the user space. -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 (4): watchdog: Extend kernel API to know about HW limitations watchdog: Allow watchdog to reset device at early boot devicetree: Document generic watchdog properties watchdog: at91sam9_wdt: Convert to use new watchdog core extensions .../devicetree/bindings/watchdog/watchdog.txt | 20 ++++ drivers/watchdog/at91sam9_wdt.c | 58 +++-------- drivers/watchdog/watchdog_core.c | 108 ++++++++++++++++++++- drivers/watchdog/watchdog_dev.c | 12 +++ include/linux/watchdog.h | 24 +++++ 5 files changed, 173 insertions(+), 49 deletions(-) create mode 100644 Documentation/devicetree/bindings/watchdog/watchdog.txt
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