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 <[EMAIL PROTECTED]>
---
Hopefully this version is correct now. :)
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 @@ void timer_interrupt(struct pt_regs * regs)
/* 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 @@ void timer_interrupt(struct pt_regs * regs)
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 @@ static int decrementer_set_next_event(unsigned long evt,
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 @@ void init_decrementer_clockevent(void)
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);
}
diff --git a/include/asm-powerpc/time.h b/include/asm-powerpc/time.h
index f058955..780f826 100644
--- a/include/asm-powerpc/time.h
+++ b/include/asm-powerpc/time.h
@@ -176,25 +176,31 @@ static inline unsigned int get_dec(void)
#endif
}
+/*
+ * Note: Book E and 4xx processors differ from other PowerPC processors
+ * in when the decrementer generates its interrupt: on the 1 to 0
+ * transition for Book E/4xx, but on the 0 to -1 transition for others.
+ */
static inline void set_dec(int val)
{
#if defined(CONFIG_40x)
mtspr(SPRN_PIT, val);
#elif defined(CONFIG_8xx_CPU6)
- set_dec_cpu6(val);
+ set_dec_cpu6(val - 1);
#else
+#ifndef CONFIG_BOOKE
+ --val;
+#endif
#ifdef CONFIG_PPC_ISERIES
- int cur_dec;
-
if (firmware_has_feature(FW_FEATURE_ISERIES) &&
get_lppaca()->shared_proc) {
get_lppaca()->virtual_decr = val;
- cur_dec = get_dec();
- if (cur_dec > val)
+ if (get_dec() > val)
HvCall_setVirtualDecr();
- } else
+ return;
+ }
#endif
- mtspr(SPRN_DEC, val);
+ mtspr(SPRN_DEC, val);
#endif /* not 40x or 8xx_CPU6 */
}
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