Re: [PATCH V2 1/3] watchdog: imgpdc: Allow timeout to be set in device-tree

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

On 04/02/2015 07:16 PM, Andrew Bresticker wrote:
> Hi Guenter,
>
> On Thu, Apr 2, 2015 at 6:52 PM, Guenter Roeck <linux@roeck-us.net> wrote:
>> On 04/02/2015 09:46 AM, Andrew Bresticker wrote:
>>>
>>> On Wed, Apr 1, 2015 at 6:08 PM, Guenter Roeck <linux@roeck-us.net> wrote:
>>>>
>>>> On 04/01/2015 03:22 PM, James Hogan wrote:
>>>>>
>>>>>
>>>>> Hi Andrew,
>>>>>
>>>>> On Wed, Apr 01, 2015 at 10:43:14AM -0700, Andrew Bresticker wrote:
>>>>>>
>>>>>>
>>>>>> Since the heartbeat is statically initialized to its default value,
>>>>>> watchdog_init_timeout() will never look in the device-tree for a
>>>>>> timeout-sec value.  Instead of statically initializing heartbeat,
>>>>>> fall back to the default timeout value if watchdog_init_timeout()
>>>>>> fails.
>>>>>
>>>>>
>>>>>
>>>>> Whoops. Sorry about that. I wasn't aware that a timeout-sec value was
>>>>> expected. It isn't mentioned in the DT binding documentation for this
>>>>> device :-(.
>>>>>
>>>>>>
>>>>>> Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
>>>>>> Cc: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
>>>>>> Cc: James Hogan <james.hogan@imgtec.com>
>>>>>> ---
>>>>>> New for v2.
>>>>>> ---
>>>>>>     drivers/watchdog/imgpdc_wdt.c | 6 +++---
>>>>>>     1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/watchdog/imgpdc_wdt.c
>>>>>> b/drivers/watchdog/imgpdc_wdt.c
>>>>>> index 0deaa4f..89b2abc 100644
>>>>>> --- a/drivers/watchdog/imgpdc_wdt.c
>>>>>> +++ b/drivers/watchdog/imgpdc_wdt.c
>>>>>> @@ -42,7 +42,7 @@
>>>>>>     #define PDC_WDT_MIN_TIMEOUT           1
>>>>>>     #define PDC_WDT_DEF_TIMEOUT           64
>>>>>>
>>>>>> -static int heartbeat = PDC_WDT_DEF_TIMEOUT;
>>>>>> +static int heartbeat;
>>>>>>     module_param(heartbeat, int, 0);
>>>>>>     MODULE_PARM_DESC(heartbeat, "Watchdog heartbeats in seconds "
>>>>>>           "(default=" __MODULE_STRING(PDC_WDT_DEF_TIMEOUT) ")");
>>>>>> @@ -195,9 +195,9 @@ static int pdc_wdt_probe(struct platform_device
>>>>>> *pdev)
>>>>>>
>>>>>>           ret = watchdog_init_timeout(&pdc_wdt->wdt_dev, heartbeat,
>>>>>> &pdev->dev);
>>>>>>           if (ret < 0) {
>>>>>> -               pdc_wdt->wdt_dev.timeout =
>>>>>> pdc_wdt->wdt_dev.max_timeout;
>>>>>> +               pdc_wdt->wdt_dev.timeout = PDC_WDT_DEF_TIMEOUT;
>>>>>
>>>>>
>>>>>
>>>>> The watchdog_init_timeout kerneldoc comment suggests that the old value
>>>>> should be the default timeout, i.e. that timeout should be set to
>>>>> PDC_WDT_DEF_TIMEOUT before calling watchdog_init_timeout, rather than
>>>>> whenever ret < 0.
>>>>>
>>>>> Indeed, if heartbeat is set to an invalid non-zero value,
>>>>> watchdog_init_timeout will still try and set timeout from DT, but also
>>>>> still returns -EINVAL regardless of whether that succeeds, and this
>>>>> would incorrectly override the timeout from DT with the hardcoded
>>>>> default.
>>>>>
>>>>>>                   dev_warn(&pdev->dev,
>>>>>> -                        "Initial timeout out of range! setting max
>>>>>> timeout\n");
>>>>>> +                        "Initial timeout out of range! setting default
>>>>>> timeout\n");
>>>>>
>>>>>
>>>>>
>>>>> It feels wrong for a presumably safe & normal situation (i.e. no default
>>>>> in DT, which arguably shouldn't contain policy anyway) to show a
>>>>> warning, but it can also show due to an invalid module parameter (or
>>>>> invalid DT property) which is most definitely justified.
>>>>>
>>>>
>>>> Agreed. I would suggest to leave that part alone and set the default
>>>> prior
>>>> to calling watchdog_init_timeout().
>>>
>>>
>>> Yes, but I think James' concern here was that we'd now get a
>>> dev_warn() in the normal case where no timeout is specified via module
>>> parameter or DT.
>>>
>> My understanding is that watchdog_init_timeout only returns an error if
>> the second parameter is not 0 and invalid, or if the timeout-sec property
>> has been provided and is invalid. I am not entirely sure I understand
>> why you think this is a problem. Can you please explain ?
>
> Unless I've gone completely insane, I'm pretty sure this will return
> -EINVAL if timeout_parm is 0 and timeout-sec is not present:
>
> int watchdog_init_timeout(struct watchdog_device *wdd,
>                                  unsigned int timeout_parm, struct device *dev)
> {
>          unsigned int t = 0;
>          int ret = 0;
>
>          watchdog_check_min_max_timeout(wdd);
>
>          /* try to get the timeout module parameter first */
>          if (!watchdog_timeout_invalid(wdd, timeout_parm) && timeout_parm) {
>                  wdd->timeout = timeout_parm;
>                  return ret;
>          }
>          if (timeout_parm)
>                  ret = -EINVAL;
>
>          /* try to get the timeout_sec property */
>          if (dev == NULL || dev->of_node == NULL)
>                  return ret;
>          of_property_read_u32(dev->of_node, "timeout-sec", &t);
>          if (!watchdog_timeout_invalid(wdd, t) && t)
>                  wdd->timeout = t;
>          else
>                  ret = -EINVAL;
>
>          return ret;
> }
>
> That said, the behavior you describe makes more sense, so perhaps
> watchdog_init_timeout() should be updated to match.
>

Ah yes, you are right, that last else case. Guess we'll need input from Wim
on how to handle this.

Guenter