[POWERPC] Fix off-by-one error in setting decrementer on Book E/4xx (v2)
The decrementer in Book E and 4xx processors interrupts on the
transition from 1 to 0, rather than on the 0 to -1 transition as on
64-bit server and 32-bit "classic" (6xx/7xx/7xxx) processors. At the
moment we subtract 1 from the count of how many decrementer ticks are
required before the next interrupt before putting it into the
decrementer, which is correct for server/classic processors, but could
possibly cause the interrupt to happen too early on Book E and 4xx if
the timebase/decrementer frequency is low.
This fixes the problem by making set_dec subtract 1 from the count for
server and classic processors, instead of having the callers subtract
1. Since set_dec already had a bunch of ifdefs to handle different
processor types, there is no net increase in ugliness. :)
Note that calling set_dec(0) may not generate an interrupt on some
processors. To make sure that decrementer_set_next_event always calls
set_dec with an interval of at least 1 tick, we set min_delta_ns of
the decrementer_clockevent to correspond to 2 ticks (2 rather than 1
to compensate for truncations in the conversions between ticks and
ns).
This also removes a redundant call to set the decrementer to
0x7fffffff - it was already set to that earlier in timer_interrupt.
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 9eb3284..99ebcd3 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -586,7 +586,7 @@
/* not time for this event yet */
now = per_cpu(decrementer_next_tb, cpu) - now;
if (now <= DECREMENTER_MAX)
- set_dec((unsigned int)now - 1);
+ set_dec((int)now);
return;
}
old_regs = set_irq_regs(regs);
@@ -611,8 +611,6 @@
if (evt->event_handler)
evt->event_handler(evt);
- else
- evt->set_next_event(DECREMENTER_MAX, evt);
#ifdef CONFIG_PPC_ISERIES
if (firmware_has_feature(FW_FEATURE_ISERIES) && hvlpevent_is_pending())
@@ -836,9 +834,6 @@
struct clock_event_device *dev)
{
__get_cpu_var(decrementer_next_tb) = get_tb_or_rtc() + evt;
- /* The decrementer interrupts on the 0 -> -1 transition */
- if (evt)
- --evt;
set_dec(evt);
return 0;
}
@@ -871,7 +866,8 @@
decrementer_clockevent.shift);
decrementer_clockevent.max_delta_ns =
clockevent_delta2ns(DECREMENTER_MAX, &decrementer_clockevent);
- decrementer_clockevent.min_delta_ns = 1000;
+ decrementer_clockevent.min_delta_ns =
+ clockevent_delta2ns(2, &decrementer_clockevent);
register_decrementer_clockevent(cpu);
}