On 26 June 2018 at 21:00, Guenter Roeck <li...@roeck-us.net> wrote: > Here is a log, with debug messages added to ptimer code.
Thanks for the logging. (I am currently also messing about with buildroot to try to reproduce -- I have a kernel that boots, but since it has no initial filesystem it hits the "stop because I can't find init" before anything interesting happens.) > Without my patch: > > ptimer_tick(0x555556edac70): enabled=1 delta=250000 limit=250000 > ptimer_reload(555556edac70): frac=0 period=40 delta=250000 limit=250000 > adjust=1 > ptimer_tick(0x555556edac70): enabled=1 delta=250000 limit=250000 > ptimer_reload(555556edac70): frac=0 period=40 delta=250000 limit=250000 > adjust=1 > [ 0.497942] clocksource: Switched to clocksource mps2-clksrc^M > ptimer_tick(0x555556edac70): enabled=1 delta=250000 limit=250000 > ptimer_reload(555556edac70): frac=0 period=40 delta=250000 limit=250000 > adjust=1 > > # up to here timer is in periodic mode and fires on a regular basis > > # prepare to switch to one-shot mode > ptimer_reload(555556edac70): frac=0 period=40 delta=0 limit=0 adjust=0 > > # set timer for one-shot mode, start > ptimer_set_count(0x555556edac70, 92004 > ptimer_reload(555556edac70): frac=0 period=40 delta=92004 limit=0 adjust=0 > > # one-shot mode fires > ptimer_tick(0x555556edac70): enabled=1 delta=92004 limit=0 > > # timer is in periodic mode, limit is 0 (from one-shot mode) > # reload propagates limit -> delta, making it 0 > ptimer_reload(555556edac70): frac=0 period=40 delta=0 limit=0 adjust=-1 > > # and the timer is disabled as result. > 0x555556edac70: Timer with delta zero, disabling > > ptimer_set_count(0x555556edac70, 199340 > ptimer_reload(555556edac70): frac=0 period=40 delta=199340 limit=0 adjust=0 > [ 0.514458] NET: Registered protocol family 2^M > ptimer_tick(0x555556edac70): enabled=1 delta=199340 limit=0 > ptimer_reload(555556edac70): frac=0 period=40 delta=0 limit=0 adjust=-1 > 0x555556edac70: Timer with delta zero, disabling > ptimer_set_count(0x555556edac70, 240488 > ptimer_reload(555556edac70): frac=0 period=40 delta=240488 limit=0 adjust=0 > [ 0.526096] tcp_listen_portaddr_hash hash table entries: 512 (order: 0, > 4096 > bytes)^M > [ 0.526533] TCP established hash table entries: 1024 (order: 0, 4096 > bytes)^M > [ 0.526943] TCP bind hash table entries: 1024 (order: 0, 4096 bytes)^M > ptimer_tick(0x555556edac70): enabled=1 delta=240488 limit=0 > ptimer_reload(555556edac70): frac=0 period=40 delta=0 limit=0 adjust=-1 > 0x555556edac70: Timer with delta zero, disabling OK, but I can't see anything actually going wrong here. Once the guest sets the RELOAD register to 0, it gets one-shot timers, and needs to write to VALUE each time to restart the timer. We seem to get calls to set_count which set different counts, and a a tick for each set_count, so that looks like it's working to me. (But see below...) > And so on. The system may finish booting or lock up. Which one it is seems > to be random. > > Same log with my patch applied: > > ptimer_tick(0x555556edac70): enabled=1 delta=250000 limit=250000 > ptimer_reload(555556edac70): frac=0 period=40 delta=250000 limit=250000 > adjust=1 > > # switch to one-shot mode > ptimer_reload(555556edac70): frac=0 period=40 delta=0 limit=0 adjust=0 > > @ set counter, start > ptimer_set_count(0x555556edac70, 24 > ptimer_reload(555556edac70): frac=0 period=40 delta=24 limit=0 adjust=0 > > # tick > ptimer_tick(0x555556edac70): enabled=2 delta=24 limit=0 > > # update counter, restart > ptimer_set_count(0x555556edac70, 209498 > ptimer_reload(555556edac70): frac=0 period=40 delta=209498 limit=0 adjust=0 > [ 0.509883] NET: Registered protocol family 2^M > > # tick > ptimer_tick(0x555556edac70): enabled=2 delta=209498 limit=0 > > # update counter, restart > ptimer_set_count(0x555556edac70, 217500 > ptimer_reload(555556edac70): frac=0 period=40 delta=217500 limit=0 adjust=0 > > # tick > ptimer_tick(0x555556edac70): enabled=2 delta=217500 limit=0 This doesn't seem to be behaving any differently (apart from having silenced the fprintf about the zero delta). My reading of the code in ptimer_tick() is that the behaviour for "this was setup as a one-shot" is in effect the same as for "this was setup as periodic but the reload value is 0" is the same: it sets enabled to 0 and delta to 0. One thing I do notice reading the code is that we don't actually do anything to re-enable the timer on a write to the VALUE register. We call ptimer_set_count(), but that will not reenable the timer if it was disabled -- the cmsdk timer code needs to call ptimer_run() if necessary, I think. But that bug should manifest whether we're setting the timer up as a one-shot or as a periodic with a 0 limit, because ptimer_tick() will disable the timer when it fires whichever way we do that. thanks -- PMM
