The patch titled hpet: hpet driver periodic timer setup bug fixes has been added to the -mm tree. Its filename is hpet-hpet-driver-periodic-timer-setup-bug-fixes.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: hpet: hpet driver periodic timer setup bug fixes From: Nils Carlson <nils.carlson@xxxxxxxxxxxx> The periodic interrupt from drivers/char/hpet.c does not work correctly, both when using the periodic capability of the hardware and while emulating the periodic interrupt (when hardware does not support periodic mode). With timers capable of periodic interrupts, the comparator field is first set with the period value followed by set of hidden accumulator, which has the side effect of overwriting the comparator value. This results in wrong periodicity for the interrupts. For, periodic interrupts to work, following steps are necessary, in that order. * Set config with Tn_VAL_SET_CNF bit * Write to hidden accumulator, the value written is the time when the first interrupt should be generated * Write compartor with period interval for subsequent interrupts (http://www.intel.com/hardwaredesign/hpetspec_1.pdf ) When emulating periodic timer with timers not capable of periodic interrupt, driver is adding the period to counter value instead of comparator value, which causes slow drift when using this emulation. Also, driver seems to add hpetp->hp_delta both while setting up periodic interrupt and while emulating periodic interrupts with timers not capable of doing periodic interrupts. This hp_delta will result in slower than expected interrupt rate and should not be used while setting the interval. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx> Signed-off-by: Nils Carlson <nils.carlson@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/char/hpet.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff -puN drivers/char/hpet.c~hpet-hpet-driver-periodic-timer-setup-bug-fixes drivers/char/hpet.c --- a/drivers/char/hpet.c~hpet-hpet-driver-periodic-timer-setup-bug-fixes +++ a/drivers/char/hpet.c @@ -166,9 +166,8 @@ static irqreturn_t hpet_interrupt(int ir unsigned long m, t; t = devp->hd_ireqfreq; - m = read_counter(&devp->hd_hpet->hpet_mc); - write_counter(t + m + devp->hd_hpets->hp_delta, - &devp->hd_timer->hpet_compare); + m = read_counter(&devp->hd_timer->hpet_compare); + write_counter(t + m, &devp->hd_timer->hpet_compare); } if (devp->hd_flags & HPET_SHARED_IRQ) @@ -504,21 +503,25 @@ static int hpet_ioctl_ieon(struct hpet_d g = v | Tn_32MODE_CNF_MASK | Tn_INT_ENB_CNF_MASK; if (devp->hd_flags & HPET_PERIODIC) { - write_counter(t, &timer->hpet_compare); g |= Tn_TYPE_CNF_MASK; - v |= Tn_TYPE_CNF_MASK; - writeq(v, &timer->hpet_config); - v |= Tn_VAL_SET_CNF_MASK; + v |= Tn_TYPE_CNF_MASK | Tn_VAL_SET_CNF_MASK; writeq(v, &timer->hpet_config); local_irq_save(flags); - /* NOTE: what we modify here is a hidden accumulator + /* + * NOTE: First we modify the hidden accumulator * register supported by periodic-capable comparators. * We never want to modify the (single) counter; that - * would affect all the comparators. + * would affect all the comparators. The value written + * is the counter value when the first interrupt is due. */ m = read_counter(&hpet->hpet_mc); write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare); + /* + * Then we modify the comparator, indicating the period + * for subsequent interrupt. + */ + write_counter(t, &timer->hpet_compare); } else { local_irq_save(flags); m = read_counter(&hpet->hpet_mc); _ Patches currently in -mm which might be from nils.carlson@xxxxxxxxxxxx are hpet-hpet-driver-periodic-timer-setup-bug-fixes.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html