forked from Minki/linux
[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>
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@ -586,7 +586,7 @@ void timer_interrupt(struct pt_regs * regs)
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/* not time for this event yet */
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now = per_cpu(decrementer_next_tb, cpu) - now;
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if (now <= DECREMENTER_MAX)
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set_dec((unsigned int)now - 1);
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set_dec((int)now);
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return;
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}
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old_regs = set_irq_regs(regs);
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@ -611,8 +611,6 @@ void timer_interrupt(struct pt_regs * regs)
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if (evt->event_handler)
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evt->event_handler(evt);
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else
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evt->set_next_event(DECREMENTER_MAX, evt);
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#ifdef CONFIG_PPC_ISERIES
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if (firmware_has_feature(FW_FEATURE_ISERIES) && hvlpevent_is_pending())
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@ -836,9 +834,6 @@ static int decrementer_set_next_event(unsigned long evt,
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struct clock_event_device *dev)
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{
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__get_cpu_var(decrementer_next_tb) = get_tb_or_rtc() + evt;
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/* The decrementer interrupts on the 0 -> -1 transition */
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if (evt)
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--evt;
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set_dec(evt);
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return 0;
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}
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@ -871,7 +866,8 @@ void init_decrementer_clockevent(void)
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decrementer_clockevent.shift);
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decrementer_clockevent.max_delta_ns =
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clockevent_delta2ns(DECREMENTER_MAX, &decrementer_clockevent);
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decrementer_clockevent.min_delta_ns = 1000;
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decrementer_clockevent.min_delta_ns =
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clockevent_delta2ns(2, &decrementer_clockevent);
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register_decrementer_clockevent(cpu);
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}
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@ -176,23 +176,29 @@ static inline unsigned int get_dec(void)
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#endif
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}
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/*
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* Note: Book E and 4xx processors differ from other PowerPC processors
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* in when the decrementer generates its interrupt: on the 1 to 0
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* transition for Book E/4xx, but on the 0 to -1 transition for others.
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*/
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static inline void set_dec(int val)
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{
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#if defined(CONFIG_40x)
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mtspr(SPRN_PIT, val);
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#elif defined(CONFIG_8xx_CPU6)
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set_dec_cpu6(val);
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set_dec_cpu6(val - 1);
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#else
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#ifndef CONFIG_BOOKE
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--val;
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#endif
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#ifdef CONFIG_PPC_ISERIES
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int cur_dec;
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if (firmware_has_feature(FW_FEATURE_ISERIES) &&
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get_lppaca()->shared_proc) {
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get_lppaca()->virtual_decr = val;
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cur_dec = get_dec();
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if (cur_dec > val)
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if (get_dec() > val)
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HvCall_setVirtualDecr();
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} else
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return;
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}
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#endif
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mtspr(SPRN_DEC, val);
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#endif /* not 40x or 8xx_CPU6 */
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