Hi Guenter,
you always can provide help very quickly, thank you very much :-)
On 23 June 2015 at 23:21, Guenter Roeck linux@roeck-us.net wrote:
On Tue, Jun 23, 2015 at 09:26:35PM +0800, Fu Wei wrote:
Hi Guenter,
[ ...]
When the first timeout occurs, WS0(SPI or LPI) is triggered,
the second timeout period(as long as the first timeout period) starts.no longer accurate if WOR is used for the second period.
In WS0 interrupt routine, panic() will be called for collecting
crashdown info.
If system can not recover from WS0 interrupt routine, then second
timeout occurs, WS1(reset or higher level interrupt) is triggered.
The two timeout period can be set by WOR(32bit).The second timeout period is determined by ...
WOR gives a maximum watch period of around 10s at the maximum
system counter frequency.
The System Counter shall run at maximum of 400MHz."... at the maximum system counter frequency of 400 MHz.", and drop the last sentence.
For the second timeout period, I have discussed with a kdump developers, (1)10s maybe not good enough for all the case of panic + kdump, so maybe we still need to use WCV in the second timeout period (2)in the second timeout period, maybe we need to programme WCV for two reason: a, trigger WS1 to reboot system ASAP; b, feed the watchdog without cleanning WS0 flag.
WHY we want to feed the watchdog (keepalive) without cleanning WS0 flag?? REASON: (1)if the system context is large, we may need to feed the dog until we get all the things backed up. (2)if system goes wrong, WS0 triggered, then panic--> kdump. if we feed the dog by WRR or programming WOR, WS0 flag will be cleaned. Once system goes wrong again, then panic again..... So this system will be in a panic--kdump--panic--kdump loop, have not chance to reset.
So if we are in the second timeout period, we may need to always programme WCV.
The crashdump kernel is supposed to reload the watchdog driver, which will ping the watchdog. If it isn't able to do that in 10 seconds, something is wrong.
yes, 10s maybe not enough for all case. When I tested kdump on arm64, sometimes , it took 20s. So I am thinking : can we make the max value of pretimeout > 10s in this driver.
status = readl_relaxed(gwdt->control_base + SBSA_GWDT_WCS);if (status & SBSA_GWDT_WCS_WS1) {dev_warn(dev, "System reset by WDT(WCV: %llx)\n",sbsa_gwdt_get_wcv(wdd));WCV here only tells us how many clock cycles were executed since the system started (or something like that). So I still don't understand why it is valuable to print that number.
this number provides the time of system reset, I thinks that may help admin to analyse the system failure.
It doesn't mean anything to anyone but you since it is not in a well defined time scale.
maybe I should convert it to second? I think the original value is better?
Also, I would be somewhat surprised if WCV would retain its value on reset. Much more likely it is the time (in clock cycles) since reset.
yes, It has been mentioned in SBSA: --------------------- If WS0 is asserted and a timeout refresh occurs then the following must occur: If the system is compliant to SBSA level 0 or level 1 then it is IMPLEMENTATION DEFINED as to whether the compare value is loaded with the sum of the zero-extended watchdog offset register and the current generic timer system count value, or whether it retains its current value. If the system is compliant to SBSA level 2 or higher the compare value must retain its current value. This means that the compare value records the time that WS1 is asserted. ---------------------
Hope I understand it correctly. please let me know , if I misunderstand something, thanks
Guenter