David Brownell <davi...@pacbell.net> writes: > On Monday 30 March 2009, Kevin Hilman wrote: >> "Mark A. Greer" <mgr...@mvista.com> writes: >> >> > On Sat, Mar 28, 2009 at 09:20:46PM -0700, David Brownell wrote: >> >> On Saturday 28 March 2009, Mark A. Greer wrote: >> >> > When enabled, the clocksource remains a continuous >> >> > 32-bit counter but the clock event will no longer >> >> > support periodic interrupts. Instead only oneshot >> >> > timers will be supported and implemented by setting >> >> > the compare register to the current timer value plus >> >> > the period that the clock event subsystem is requesting. >> >> >> >> How well stress tested is that mode? >> >> >> >> Thing is, it's inherently racey because the "current" >> >> timer is counting up while you're setting the compare >> >> register. Maybe it incremented just after you read it. >> >> That normally means min_delta_ns for the clockevent needs >> >> to be at least two ticks ... ideally several more than >> >> that, on the order of an IRQ latency, >> > >> > Yes, it is racey and I ran into the race when I had some >> > printk's in it during debugging. I bumped up >> > clockevent_davinci.min_delta_ns until they went away. >> > The printk's added so many artifacts that it wasn't valid >> > testing, though. >> > >> >> For the record this is quite like HPET on x86, where >> >> there's one counter (used in 32-bit mode even though >> >> it may well support 64-bits) and a bunch of compare >> >> registers (32 bit, almost always) to generate IRQs. >> > >> > I did test it doing more-or-less "normal" things but >> > I don't believe the true min is 1ns. :) >> > >> > I'll do some experimenting and come up with a better >> > value. >> > >> >> Maybe a test patch that converts dm644x, dm355, and dm646x to use a >> single timer would allow broader testing of this as well. > > Wouldn't be quite the same. Those don't actually have > compare registers which work that way...
doh! of course. Kevin _______________________________________________ Davinci-linux-open-source mailing list Davinci-linux-open-source@linux.davincidsp.com http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source
