Messages in this thread | | | Date | Thu, 21 May 2015 03:17:28 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH v2 5/7] Watchdog: introduce "pretimeout" into framework |
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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@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 >
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
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