Le 11/03/2015 09:38, Boris Brezillon a écrit : > On Sun, 08 Mar 2015 02:11:45 +0100 > "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> wrote: > >> On Saturday, March 07, 2015 12:06:45 PM Alexandre Belloni wrote: >>> On 07/03/2015 at 11:39:39 +0100, Pavel Machek wrote : >>>>> The Atmel watchdog can't be stopped once it's started. This is actually >>>>> very useful so we can reset if suspend or resume failed, the only >>>>> drawback is that you have to wake up from time to time (e.g. by using >>>>> the RTC/RTT) to clear the watchdog and then go back to sleep ASAP. >>>> >>>> Yeah. So you do "echo mem > /sys/power/state", and few seconds/minutes >>>> after watchdog kills the system. But you did not ask for dead system, >>>> you asked for suspend. >>>> >>>> And while that behaviour is useful for you, I don't think it is >>>> exactly useful behaviour, nor it is the behaviour user would expect. >>>> >>> >>> I think you misunderstood, that is exactly the expected behaviour. This >>> is hardware defined. Once the watchdog is started, nobody can stop it. >>> Trying to change the mode register will result in a reset of the SoC. >>> >>> It is documented in the datasheet and any user wanting another behaviour >>> is out of luck. >>> >>> So basically, when using a watchdog, you have to wake up every 15-16s to >>> restart it. >> >> So question is if we need a separate interrupt handler for that, expecially >> since it is shared with the PIT timer anyway. >> >> Seems to me that the simplest way out of this conundrum would be to simply >> make the timer's interrupt handler kick the watchdog every once a while and >> get rid of the separate watchdog interrupt handler entirely. > > The watchdog interrupt handler is not here to ping the watchdog, it's > here to reset the platform if the watchdog hasn't been refreshed > appropriately. > > IOW, it's a software watchdog using at91 WDT capabilities to determine > when it should reboot the system. > IIRC, we need this on some at91 platforms to fix a HW bug (maybe > Nicolas can confirm this). Yes, the HW bug that we address in these functions: at91sam9260_restart() and at91sam9g45_restart(). We have this issue because of NAND flash lines shared with DDR that are driven during product reboot on old products (Cf. these functions comments). This bug would kick-in when doing "software reset"/"watchdog reset"/"push button reset". Only the "software reset" is handled by the functions above. So, yes, this "software watchdog" is there for this purpose IIRC. Bye, -- Nicolas Ferre -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
