> 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. 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
