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SubjectRe: [PATCH v2 5/7] Watchdog: introduce "pretimeout" into framework
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Hi Guenter,

Thanks for review. :-)
feedback inline below

On 21 May 2015 at 17:04, Guenter Roeck <linux@roeck-us.net> wrote:
> On 05/21/2015 01:32 AM, fu.wei@linaro.org wrote:
>>
>> From: Fu Wei <fu.wei@linaro.org>
>>
>> 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@linaro.org>
>> ---
>
>
> [ ... ]
>
>> +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

>
> 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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