Subject: [PATCH] at91sam9_wdt: Allow watchdog to reset device at early boot

From: [email-masked] (Guenter Roeck)
Date: Thu, 27 Nov 2014 09:23:30 -0800

On 11/27/2014 01:22 AM, Nicolas Ferre wrote:
> On 27/11/2014 07:53, Timo Kokkonen wrote:
>> Hi,
>>
>> On 21.11.2014 14:23, Timo Kokkonen wrote:
>>> By default the driver will start a kernel timer which keeps on kicking
>>> the watchdog HW until user space has opened the watchdog
>>> device. Usually this is desirable as the watchdog HW is running by
>>> default and the user space may not have any watchdog daemon running at
>>> all.
>>>
>>> However, on production systems it may be mandatory that also early
>>> crashes and lockups will lead to a watchdog reset, even if they happen
>>> before the user space has opened the watchdog device.
>>>
>>> To resolve the issue, add a new device tree property
>>> "enable-early-reset" which will prevent the kernel timer from pinging
>>> the watchdog HW on behalf of user space. The default is still to use
>>> kernel timer, but more strict behavior can be enabled via the device
>>> tree property.
>>>
>>> Signed-off-by: Timo Kokkonen <[email-masked]>
>>
>> I forgot to put the PATCHv2 on the subject line.. But anyway, any
>> thoughts about it? Is there something that should be done to get it forward?
>
> Sorry for not having come back to you quickly.
>
> The only thing that tend to prevent me from taking this patch is the
> fact that this DT property is mostly a software, Linux-specific one...
> Which is somehow not covered by the DT.
> This might explain as well why this property is not present on other SoCs.
>
> Can we have other people's advices?
>

We have been thinking about a more generic (infrastructure based) solution
for the problem at hand, but that was a bit more complex and would specify
the actual timeout during boot, not just a boolean like suggested here.

As for DT not supposed to be used for configuration, that is really a
tricky problem which is hard to solve. I seem to recall, though, that
it may be now acceptable under certain conditions. A module parameter
might be easier.

Guenter

> Bye,
>
>>> ---
>>>    Documentation/devicetree/bindings/watchdog/atmel-wdt.txt | 4 ++++
>>>    drivers/watchdog/at91sam9_wdt.c                          | 6 +++++-
>>>    2 files changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
>>> index f90e294..a0b7b75 100644
>>> --- a/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
>>> +++ b/Documentation/devicetree/bindings/watchdog/atmel-wdt.txt
>>> @@ -28,6 +28,10 @@ Optional properties:
>>>    	entering idle state.
>>>    - atmel,dbg-halt : Should be present if you want to stop the watchdog when
>>>    	entering debug state.
>>> +- enable-early-reset : Should be present if you want to let the
>>> +	watchdog timer to expire even before user space has opened the
>>> +	device. If not set, a kernel timer will keep on pinging the
>>> +	watchdog until it is opened.
>>>
>>>    Example:
>>>    	watchdog at fffffd40 {
>>> diff --git a/drivers/watchdog/at91sam9_wdt.c b/drivers/watchdog/at91sam9_wdt.c
>>> index 489729b..78b1977 100644
>>> --- a/drivers/watchdog/at91sam9_wdt.c
>>> +++ b/drivers/watchdog/at91sam9_wdt.c
>>> @@ -89,6 +89,7 @@ struct at91wdt {
>>>    	u32 mr_mask;
>>>    	unsigned long heartbeat;	/* WDT heartbeat in jiffies */
>>>    	bool nowayout;
>>> +	bool no_early_timer;
>>>    	unsigned int irq;
>>>    };
>>>
>>> @@ -122,7 +123,7 @@ static void at91_ping(unsigned long data)
>>>    {
>>>    	struct at91wdt *wdt = (struct at91wdt *)data;
>>>    	if (time_before(jiffies, wdt->next_heartbeat) ||
>>> -	    !watchdog_active(&wdt->wdd)) {
>>> +		(!watchdog_active(&wdt->wdd) && !wdt->no_early_timer)) {
>>>    		at91_wdt_reset(wdt);
>>>    		mod_timer(&wdt->timer, jiffies + wdt->heartbeat);
>>>    	} else {
>>> @@ -316,6 +317,9 @@ static int of_at91wdt_init(struct device_node *np, struct at91wdt *wdt)
>>>
>>>    	wdt->mr |= max | ((max - min) << 16);
>>>
>>> +	if (of_property_read_bool(np, "enable-early-reset"))
>>> +		wdt->no_early_timer = 1;
>>> +
>>>    	return 0;
>>>    }
>>>    #else
>>>
>>
>>
>
>