From 43875cc0a54d936132010e58545269e183741fae Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Wed, 31 Oct 2007 22:25:35 +1100 Subject: [PATCH] [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 --- arch/powerpc/kernel/time.c | 10 +++------- include/asm-powerpc/time.h | 20 +++++++++++++------- 2 files changed, 16 insertions(+), 14 deletions(-) diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 9eb3284deac4..99ebcd3884d2 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 f05895522f7f..780f82642756 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 */ } -- 2.20.1