src/patches/suse-2.6.27.39/patches.fixes/hpet-correct-periodic-intr.patch

   1 From: Nils Carlson <nils.carlson@ericsson.com>
   2 Subject: hpet: hpet driver periodic timer setup bug fixes
   3 References: bnc#515640
   4 Patch-mainline: queued
   5
   6
   7 The periodic interrupt from drivers/char/hpet.c does not work correctly,
   8 both when using the periodic capability of the hardware and while
   9 emulating the periodic interrupt (when hardware does not support
  10 periodic mode).
  11
  12 With timers capable of periodic interrupts, the comparator field is first
  13 set with the period value followed by set of hidden accumulator,
  14 which has the side effect of overwriting the comparator value. This
  15 results in wrong periodicity for the interrupts. For,
  16 periodic interrupts to work, following steps are necessary, in that order.
  17 * Set config with Tn_VAL_SET_CNF bit
  18 * Write to hidden accumulator, the value written is the time when the
  19   first interrupt should be generated
  20 * Write compartor with period interval for subsequent interrupts
  21 (http://www.intel.com/hardwaredesign/hpetspec_1.pdf )
  22
  23 When emulating periodic timer with timers not capable of periodic
  24 interrupt, driver is adding the period to counter value instead of
  25 comparator value, which causes slow drift when using this emulation.
  26
  27 Also, driver seems to add hpetp->hp_delta both while setting up
  28 periodic interrupt and while emulating periodic interrupts with timers
  29 not capable of doing periodic interrupts. This hp_delta will result in
  30 slower than expected interrupt rate and should not be used while setting
  31 the interval.
  32
  33 Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
  34 Signed-off-by: Nils Carlson <nils.carlson@ericsson.com>
  35 Acked-by: Goldwyn Rodrigues <rgoldwyn@suse.de>
  36
  37 ---
  38  drivers/char/hpet.c |   23 ++++++++++++++++-------
  39  1 file changed, 16 insertions(+), 7 deletions(-)
  40
  41 Index: linux-2.6.27-SLE11_BRANCH/drivers/char/hpet.c
  42 ===================================================================
  43 --- linux-2.6.27-SLE11_BRANCH.orig/drivers/char/hpet.c  2008-10-09 17:13:53.000000000 -0500
  44 +++ linux-2.6.27-SLE11_BRANCH/drivers/char/hpet.c       2009-08-28 09:58:42.000000000 -0500
  45 @@ -164,9 +164,9 @@ static irqreturn_t hpet_interrupt(int ir
  46                 unsigned long m, t;
  47
  48                 t = devp->hd_ireqfreq;
  49 -               m = read_counter(&devp->hd_hpet->hpet_mc);
  50 -               write_counter(t + m + devp->hd_hpets->hp_delta,
  51 -                             &devp->hd_timer->hpet_compare);
  52 +               m = read_counter(&devp->hd_timer->hpet_compare);
  53 +               write_counter(t + m, &devp->hd_timer->hpet_compare);
  54 +
  55         }
  56
  57         if (devp->hd_flags & HPET_SHARED_IRQ)
  58 @@ -444,15 +444,24 @@ static int hpet_ioctl_ieon(struct hpet_d
  59         g = v | Tn_INT_ENB_CNF_MASK;
  60
  61         if (devp->hd_flags & HPET_PERIODIC) {
  62 -               write_counter(t, &timer->hpet_compare);
  63                 g |= Tn_TYPE_CNF_MASK;
  64 -               v |= Tn_TYPE_CNF_MASK;
  65 -               writeq(v, &timer->hpet_config);
  66 -               v |= Tn_VAL_SET_CNF_MASK;
  67 +               v |= Tn_TYPE_CNF_MASK | Tn_VAL_SET_CNF_MASK;
  68                 writeq(v, &timer->hpet_config);
  69                 local_irq_save(flags);
  70 +               /*
  71 +                * NOTE: First we modify the hidden accumulator
  72 +                * register supported by periodic-capable comparators.
  73 +                * We never want to modify the (single) counter; that
  74 +                * would affect all the comparators. The value written
  75 +                * is the counter value when the first interrupt is due.
  76 +                */
  77                 m = read_counter(&hpet->hpet_mc);
  78                 write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
  79 +               /*
  80 +                * Then we modify the comparator, indicating the period
  81 +                * for subsequent interrupt.
  82 +                */
  83 +               write_counter(t, &timer->hpet_compare);
  84         } else {
  85                 local_irq_save(flags);
  86                 m = read_counter(&hpet->hpet_mc);