Re: [PATCH] watchdog: bcm47xx_wdt.c: add restart handler support

[Guenter Roeck <linux@roeck-us.net>]

On 01/24/2015 09:31 AM, Rafał Miłecki wrote:
> On 24 January 2015 at 17:54, Guenter Roeck <linux@roeck-us.net> wrote:
>> On 01/24/2015 08:45 AM, Rafał Miłecki wrote:
>>>
>>> On 24 January 2015 at 17:32, Guenter Roeck <linux@roeck-us.net> wrote:
>>>>
>>>> On 01/24/2015 05:47 AM, Rafał Miłecki wrote:
>>>>>
>>>>>
>>>>> Just like in case of other watchdog drivers, use the new kernel core
>>>>> API to provide restart support.
>>>>>
>>>>> Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
>>>>> ---
>>>>>     drivers/watchdog/bcm47xx_wdt.c | 22 ++++++++++++++++++++--
>>>>>     1 file changed, 20 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/watchdog/bcm47xx_wdt.c
>>>>> b/drivers/watchdog/bcm47xx_wdt.c
>>>>> index 9816485..dac3c5d 100644
>>>>> --- a/drivers/watchdog/bcm47xx_wdt.c
>>>>> +++ b/drivers/watchdog/bcm47xx_wdt.c
>>>>> @@ -169,6 +169,17 @@ static int bcm47xx_wdt_notify_sys(struct
>>>>> notifier_block *this,
>>>>>           return NOTIFY_DONE;
>>>>>     }
>>>>>
>>>>> +static int bcm47xx_wdt_restart(struct notifier_block *this, unsigned
>>>>> long
>>>>> mode,
>>>>> +                              void *cmd)
>>>>> +{
>>>>> +       struct bcm47xx_wdt *wdt;
>>>>> +
>>>>> +       wdt = container_of(this, struct bcm47xx_wdt, restart_handler);
>>>>> +       wdt->timer_set(wdt, 1);
>>>>> +
>>>>> +       return NOTIFY_DONE;
>>>>> +}
>>>>> +
>>>>>     static struct watchdog_ops bcm47xx_wdt_soft_ops = {
>>>>>           .owner          = THIS_MODULE,
>>>>>           .start          = bcm47xx_wdt_soft_start,
>>>>> @@ -204,20 +215,27 @@ static int bcm47xx_wdt_probe(struct
>>>>> platform_device
>>>>> *pdev)
>>>>>           watchdog_set_nowayout(&wdt->wdd, nowayout);
>>>>>
>>>>>           wdt->notifier.notifier_call = &bcm47xx_wdt_notify_sys;
>>>>> -
>>>>>           ret = register_reboot_notifier(&wdt->notifier);
>>>>>           if (ret)
>>>>>                   goto err_timer;
>>>>>
>>>>> -       ret = watchdog_register_device(&wdt->wdd);
>>>>> +       wdt->restart_handler.notifier_call = &bcm47xx_wdt_restart;
>>>>> +       wdt->restart_handler.priority = 128;
>>>>
>>>>
>>>>
>>>> This should be low priority since it doesn't immediately restart the
>>>> system
>>>> but uses a watchdog timeout.
>>>
>>>
>>> I think this is also the only way to reboot Broadcom device. Is there
>>> some howto on values I should use? Should I change it to sth like 64?
>>> Or what number?
>>>
>>
>> 64 is fine.
>>
>> You never know if someone using that chip implements, for example, reset
>> with a gpio pin.
>
> Sure, that's why I wanted to left 129-255 values for other situations.
> As watchdog reset is used in 99% of cases, I wanted to use the middle
> priority for it.
>
... and then forcing everyone else to use a higher priority than 128,
resulting in a priority war. Guess those who predicted that this would
happen were right after all :-(.

> Actually it seems that currently every watchdog driver with restart
> handler uses priority 128. This includes: alim7101_wdt.c dw_wdt.c
> imx2_wdt.c meson_wdt.c moxart_wdt.c s3c2410_wdt.c sunxi_wdt.c
>
> Are you sure this value 128 is wrong in case of bcm47xx_wdt? What
> makes it alright for all other drivers?
>
The other drivers do not use a watchdog timeout to accomplish an indirect
restart, but use a register from the set of registers used by the watchdog
driver to implement the restart. Or at least that is how it should be.

Guenter