Re: [PATCH v2 5/7] Watchdog: introduce "pretimeout" into framework

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Hi Guenter,

Great thanks, I have got your review feedback, I will fix the problems :-)
For update_limits, I also don't want to have that in the watchdog
driver, and you can't find it in my last version.
And this version, I integrate the watchdog_init_timeout and
watchdog_init_pretimeout. so I can not add a  driver specific
"update_limits" between them.
I think maybe we can not make this "update_limits" after calling
init_timeouts, because we need to test and verify the timeout setting
right after init_pretimeout by max_timeout and min_timeout. that is
why I call update_limits right after init_pretimeout and before
init_timeout.

any suggestion ?  Great thanks !  :-)

On 21 May 2015 at 18:17, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On 05/21/2015 03:05 AM, Fu Wei wrote:
>>
>> Hi Guenter,
>>
>> Thanks for review. :-)
>> feedback inline below
>>
>> On 21 May 2015 at 17:04, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>>>
>>> On 05/21/2015 01:32 AM, fu.wei@xxxxxxxxxx wrote:
>>>>
>>>>
>>>> From: Fu Wei <fu.wei@xxxxxxxxxx>
>>>>
>>>> Also update Documentation/watchdog/watchdog-kernel-api.txt to
>>>> introduce:
>>>> (1)the new elements in the watchdog_device and watchdog_ops struct;
>>>> (2)the new API "watchdog_init_timeouts".
>>>>
>>>> Reasons:
>>>> (1)kernel already has two watchdog drivers are using "pretimeout":
>>>>          drivers/char/ipmi/ipmi_watchdog.c
>>>>          drivers/watchdog/kempld_wdt.c(but the definition is different)
>>>> (2)some other dirvers are going to use this: ARM SBSA Generic Watchdog
>>>>
>>>> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
>>>> ---
>>>
>>>
>>>
>>> [ ... ]
>>>
>>>> +extern int watchdog_init_timeouts(struct watchdog_device *wdd,
>>>> +                                  unsigned int pretimeout_parm,
>>>> +                                  unsigned int timeout_parm,
>>>> +                                  void (*update_limits)(struct
>>>> watchdog_device *),
>>>> +                                  struct device *dev);
>>>>
>>>> -The watchdog_init_timeout function allows you to initialize the timeout
>>>> field
>>>> -using the module timeout parameter or by retrieving the timeout-sec
>>>> property from
>>>> -the device tree (if the module timeout parameter is invalid). Best
>>>> practice is
>>>> -to set the default timeout value as timeout value in the
>>>> watchdog_device
>>>> and
>>>> -then use this function to set the user "preferred" timeout value.
>>>> +The watchdog_init_timeouts function allows you to initialize the
>>>> pretimeout and
>>>> +timeout fields using the module pretimeout and timeout parameter or by
>>>> +retrieving the elements in the timeout-sec property(the first element
>>>> is
>>>> for
>>>> +timeout, the second one is for pretimeout) from the device tree(if the
>>>> module
>>>> +pretimeout and timeout parameter are invalid).
>>>> +Normally, the pretimeout value will affect the limitation of timeout,
>>>> and
>>>> it
>>>> +is also hardware related. So you can write a function in your driver to
>>>> update
>>>> +the limitation of timeout, according to the pretimeout value. Then pass
>>>> the
>>>> +function pointer by the update_limits parameter. If you driver doesn't
>>>> +need this adjustment, just pass NULL to the update_limits parameter.
>>>
>>>
>>>
>>> You've lost me a bit with the update_limits function.
>>> watchdog_init_timeouts()
>>> is called from the driver.
>>
>>
>> yes, that is the help function which will be called from watchdog
>> driver, like SBSA watchdog driver
>>
>>> Why should the function have to call back into
>>> the
>>> driver to update the parameters which are passed from the driver ?
>>
>>
>> Let me explain this, please correct me if I misunderstand something.
>> According to the concept of "pretimeout" in kernel, the timeout
>> contains the pretimeout, like
>>
>>   * Kernel/API:                         P---------| pretimeout
>>   *                      |-------------------------------T timeout
>>
>> If you set up the value of pretimeout, that means pretimeout
>> <min_timeout < timeout < max_timeout < (pretimeout +
>> max_timeout_for_1th_stage)
>> For  min_timeout > pretimeout.  if some one setup a timeout like :
>> pretimeout >  timeout > min_timeout, I think that could be a problem
>> For  max_timeout < (pretimeout + max_timeout_for_1th_stage),  if some
>> one setup a timeout like (pretimeout + max_timeout_for_1th_stage) <
>> timeout >  max_timeout .
>>
>> I have explained a little in doc, but the adjustment may have
>> something to do with hardware, like  max_timeout_for_1th_stage(in SBSA
>> watchdog , limited by WCV)
>>
>> maybe this problem wouldn't happen ,if you set up  max_timeout to a
>> small number. so you can pass NULL to the pointer.
>>   but I think maybe for other device , that may happen.
>>
>>> Seems to me the driver can do that calculation first, then call
>>> watchdog_init_timeouts() with the result. Am I missing something ?
>>
>>
>> maybe I am overthinking it :-)
>> please correct me
>>
>
> I just sent a more complete review. In general I think this problem
> (where the driver needs to update timeout limits based on the value of
> pretimeout) is very driver specific, and should be kept in the driver.
> I would prefer to keep it out of the API if possible.
>
> Unless I am missing something, it should be possible to call the
> update_limits function in the driver after calling init_timeouts.
>
> Thanks,
> Guenter
>



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch
Ph: +86 21 61221326(direct)
Ph: +86 186 2020 4684 (mobile)
Room 1512, Regus One Corporate Avenue,Level 15,
One Corporate Avenue,222 Hubin Road,Huangpu District,
Shanghai,China 200021
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