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)(structwatchdog_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 timeoutIf 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