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[POWERPC] Fix off-by-one error in setting decrementer on Book E/4xx (v2)

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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>
This commit is contained in:
Paul Mackerras 2007-10-31 22:25:35 +11:00
parent 465ccab9eb
commit 43875cc0a5
2 changed files with 16 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
arch/powerpc/kernel/time.c
View File

@ -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);
}

20
include/asm-powerpc/time.h
View File

@ -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 */
}