[PATCHv6 0/4] watchdog: Extend kernel API and add early_timeout_sec feature

[Yang, Wenyou]

> -----Original Message-----
> From: Timo Kokkonen [mailto:timo.kokkonen at offcode.fi]
> Sent: 2015年4月14日 15:27
> To: linux-arm-kernel at lists.infradead.org; linux-watchdog at vger.kernel.org;
> boris.brezillon at free-electrons.com; Ferre, Nicolas; alexandre.belloni at free-
> electrons.com
> Cc: Yang, Wenyou; Timo Kokkonen
> Subject: [PATCHv6 0/4] watchdog: Extend kernel API and add early_timeout_sec
> feature
> 
> 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. This patch set
> converts at91sam9_wdt to use the new API.
> 
> Please review and give feedback.

Tested on sama5d4ek, it works fine.

> 
> Patch revision history:
> 
> -v6: Fixed some issued based on feedback from Wenyou Yang. The logic
>   in watchdog_worker() function is now significantly easier to
>   read. Several errors with stopping and starting the worker are also
>   now fixed.
> 
> -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                   | 124 ++++++++++++++++++++-
>  drivers/watchdog/watchdog_dev.c                    |  26 ++++-
>  include/linux/watchdog.h                           |  24 ++++
>  5 files changed, 201 insertions(+), 51 deletions(-)  create mode 100644
> Documentation/devicetree/bindings/watchdog/watchdog.txt
> 
> --
> 2.1.0

Best Regards,
Wenyou Yang