On Apr 28, 2016, at 12:25 PM, John Syne <john3909@xxxxxxxxx> wrote: > >> >> On Apr 28, 2016, at 5:44 AM, John Syne <john3909@xxxxxxxxx> wrote: >> >> >> >>> On Apr 28, 2016, at 1:14 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: >>> >>> On Wed, 27 Apr 2016, John Syne wrote: >>> >>>> I’m attempting to add DMA support to the ti_am335x_adc driver but when >>>> running the Lauterback debugger, I get strange timer corruption and the >>>> kernel completely loops forever in include/linux/math64.h and takes the >>>> “bhi” branch below and never gets to C00BB2A0. >>> >>>> So here is what I see after single stepping and running and stopping several >>>> times. As you can see, the timer is negative and this is causing a lockup. I >>>> have seen the same occur with timekeeping_get_ns where delta is negative ( >>>> tkr->cycle_last occurs after cycle_now) . Seems like a race condition. Does >>> >>> It's not a race condition. By stopping the kernel you make the clocksource >>> wrap around resulting in a negative delta. >> That makes sense, however it seems that clocksource wraps every 172 seconds, which doesn’t make sense to me. Given a 32 bit number, I would expect clocksource to wrap every 2,147 seconds. What am I missing? >>> >>>> anyone have any idea as to why this would be happening, or alternatively, >>>> how can I just cleanup this up when I get a negative value. I tried setting >>>> tkr->cycle_last = cycle_now, but that didn’t work. >>> >>> Enabling CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE should fix that issue. >> Thanks Thomas. I’ll give that a try. > I see that CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE is only defined for x86 in that it is included in arch/x86/Kconfig. Cannot select it with > make xconfig > > My guess is I can do the same with arch/arm/Kconfig and add > > select CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE in config ARM section. > > Does that sound correct? Hi Thomas, I made this change and it does seem to be working. I have not seen any lockups while using Lauterbach single stepping since making this change. Thank you for all your help. Regards, John > > Regards, > John >> >> Regards, >> John >>> >>> Thanks, >>> >>> tglx -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
