Hi Timo, On 22 May 2015 at 16:59, Timo Kokkonen <timo.kokko...@offcode.fi> wrote: > On 22.05.2015 11:23, Fu Wei wrote: >> >> Hi Timo, >> >> >> On 22 May 2015 at 14:30, Timo Kokkonen <timo.kokko...@offcode.fi> wrote: >>> >>> On 21.05.2015 11:32, fu....@linaro.org wrote: >>>> >>>> >>>> From: Fu Wei <fu....@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 >>>> >>> >>> Hi, >>> >>> As I was proposing some other API changes with my early-timeout-sec work, >>> I >>> can see my work is going to collide with your API change proposal a bit. >>> So >>> maybe I should ask your opinion as well.. >> >> >> Thank you for reminding me of that, I saw "early-timeout-sec", but >> because I don't get it in kernel API or watchdog_core.c, so I did not >> pay attention to it. >> Sorry. >> >>> >>> Could this pretimeout feature be something that other drivers could >>> benefit >>> too? >> >> >> yes , as you may know, I am making a patch for pretimeout support in >> watchdog framework >> >>> I can see that it does not do anything else except call panic() before >>> letting the watchdog expire. This is something that could be emulated >>> easily >>> by the watchdog core for drivers that don't know anything about >>> pretimeouts >>> at all. >> >> >> For SBSA watchdog, there are two stage timeout, and according to kernel >> doc: >> ---------------------- >> Pretimeouts: >> >> Some watchdog timers can be set to have a trigger go off before the >> actual time they will reset the system. This can be done with an NMI, >> interrupt, or other mechanism. This allows Linux to record useful >> information (like panic information and kernel coredumps) before it >> resets. >> ---------------------- >> >> I think panic() is the right way to do now. but people may also need >> to config : >> PANIC_TIMEOUT [!=0] >> KEXEC >> KDUMP >> for debug reason >> > > Yes, so basically if we hit pretimeout, we probably have already crashed.
yes, for now , I only use panic(), but at the beginning, I offer user some options: https://lists.linaro.org/pipermail/linaro-acpi/2015-April/004350.html > The only difference is that we now have some seconds time to dump out useful > data and then either reboot or let the actual watchdog reset take care of > resetting the device. panic() sounds like a good thing to do. Maybe you > could also dump registers on other CPUs too or try to get out some other > useful information about the kernel in case it has crashed or something. But > I'm just guessing. yes, that is my thought. because there is the kdump support in panic(), so that can give use a chance to figure out why the watchdog wasn't fed. > >>> >>> The way I was planning the API change there would need to be a small >>> change >>> with each watchdog driver in order to let the watchdog core take over >>> generic behaviour on behalf of the driver. My goal was to make the change >>> so >>> that each driver that gets converted to the new API extensions gets a >>> support for early-timeout-sec for free, without needing to enable support >>> for it any way. If the API was designed properly, also pretimeouts could >>> be >>> handled easily and maybe even so that other drivers could have that >>> feature >>> even though their hardware does not explicitly give any support for it. >> >> >> could you please point out your patch , then I can learn your idea :-) >> For now , I am working on a common "Pretimeouts" following the concept >> in kernel doc. >> >>> >>> Any thoughts? >> >> >> my thoughts is in my pretimeout patch , would you provide some suggestion >> ? >> > > Here is an archive link to my patch set: > > http://www.spinics.net/lists/linux-watchdog/msg06473.html Ah , cool, I can see some common in your patch. Thanks :-) See if I can learn something from your patches > > Your patch set is adding a new call to the core for adjusting the > pretimoeut, which is probably a good thing in case the driver needs special > handling for it anyway. But if the core had capability to emulate pretimeout > for drivers that can't support it in hardware, it would be good if there was > a way for the core to support it even though the driver had zero code for > it. The core also has watchdog_init_timeout() right now but even that is not > called from that many drivers. I would like to fix that too so that drivers > would not need to bother so much about it but let core take care of it more. > This is why I proposed the watchdog_init_params() call that could dig all > the generic parameters from device tree on behalf of the driver. This is > where I though timeout and early-timeout-sec parameters would be parsed from > device tree, but it could also parse pretimeout parameter as well. > Apparently Guenter did not like my approach so we might need some other way > to do it. I am using pretimeout, because SBSA watchdog hardware support two stages timeout, I am reusing the existing kernel concept, but your early_timeout_sec is a new concept. If you check my previous patchset , you will see : at the beginning, pretimeout support is not a generic features in my patchset. Then Arnd suggest that I can try to make pretimeout into watchdog framework, and Guenter said :"Makes sense." So I am still trying to improve pretimeout support :-) If I can make pretimeout merged, may be you can try pretimeout to implement early_timeout_sec function? It is up to the maintainers, I will try my best. Thanks :-) > > I don't get to say how this should be done, I'm just throwing ideas here. > But I think the watchdog core would be a lot better place for implementing > the generic features than drivers. That way a lot of drivers could enable > support the new features for free. > > Thanks, > -Timo -- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
