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3b950de9c9
Prevent cnt32_to_63() from being preempted in sched_clock() because it may read its internal counter, get preempted, get delayed for more than the half period of the 'TSC' and then write the internal counter, thus corrupting it. Whilst some callers of sched_clock() have interrupts disabled or hold spinlocks, not all do, and so preemption must be held here. Note that sched_clock() is called from lockdep, but that shouldn't be a problem because although preempt_disable() calls into lockdep, lockdep has a recursion counter to deal with this. Signed-off-by: David Howells <dhowells@redhat.com>
161 lines
4.2 KiB
C
161 lines
4.2 KiB
C
/* MN10300 Low level time management
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*
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* Copyright (C) 2007-2008 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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* - Derived from arch/i386/kernel/time.c
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/interrupt.h>
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#include <linux/time.h>
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#include <linux/init.h>
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#include <linux/smp.h>
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#include <linux/profile.h>
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#include <linux/cnt32_to_63.h>
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#include <asm/irq.h>
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#include <asm/div64.h>
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#include <asm/processor.h>
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#include <asm/intctl-regs.h>
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#include <asm/rtc.h>
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#ifdef CONFIG_MN10300_RTC
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unsigned long mn10300_ioclk; /* system I/O clock frequency */
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unsigned long mn10300_iobclk; /* system I/O clock frequency */
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unsigned long mn10300_tsc_per_HZ; /* number of ioclks per jiffy */
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#endif /* CONFIG_MN10300_RTC */
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static unsigned long mn10300_last_tsc; /* time-stamp counter at last time
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* interrupt occurred */
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static irqreturn_t timer_interrupt(int irq, void *dev_id);
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static struct irqaction timer_irq = {
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.handler = timer_interrupt,
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.flags = IRQF_DISABLED | IRQF_SHARED | IRQF_TIMER,
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.name = "timer",
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};
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static unsigned long sched_clock_multiplier;
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/*
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* scheduler clock - returns current time in nanosec units.
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*/
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unsigned long long sched_clock(void)
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{
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union {
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unsigned long long ll;
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unsigned l[2];
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} tsc64, result;
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unsigned long tsc, tmp;
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unsigned product[3]; /* 96-bit intermediate value */
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/* cnt32_to_63() is not safe with preemption */
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preempt_disable();
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/* read the TSC value
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*/
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tsc = 0 - get_cycles(); /* get_cycles() counts down */
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/* expand to 64-bits.
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* - sched_clock() must be called once a minute or better or the
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* following will go horribly wrong - see cnt32_to_63()
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*/
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tsc64.ll = cnt32_to_63(tsc) & 0x7fffffffffffffffULL;
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preempt_enable();
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/* scale the 64-bit TSC value to a nanosecond value via a 96-bit
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* intermediate
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*/
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asm("mulu %2,%0,%3,%0 \n" /* LSW * mult -> 0:%3:%0 */
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"mulu %2,%1,%2,%1 \n" /* MSW * mult -> %2:%1:0 */
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"add %3,%1 \n"
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"addc 0,%2 \n" /* result in %2:%1:%0 */
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: "=r"(product[0]), "=r"(product[1]), "=r"(product[2]), "=r"(tmp)
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: "0"(tsc64.l[0]), "1"(tsc64.l[1]), "2"(sched_clock_multiplier)
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: "cc");
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result.l[0] = product[1] << 16 | product[0] >> 16;
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result.l[1] = product[2] << 16 | product[1] >> 16;
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return result.ll;
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}
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/*
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* initialise the scheduler clock
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*/
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static void __init mn10300_sched_clock_init(void)
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{
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sched_clock_multiplier =
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__muldiv64u(NSEC_PER_SEC, 1 << 16, MN10300_TSCCLK);
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}
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/*
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* advance the kernel's time keeping clocks (xtime and jiffies)
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* - we use Timer 0 & 1 cascaded as a clock to nudge us the next time
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* there's a need to update
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*/
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static irqreturn_t timer_interrupt(int irq, void *dev_id)
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{
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unsigned tsc, elapse;
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write_seqlock(&xtime_lock);
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while (tsc = get_cycles(),
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elapse = mn10300_last_tsc - tsc, /* time elapsed since last
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* tick */
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elapse > MN10300_TSC_PER_HZ
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) {
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mn10300_last_tsc -= MN10300_TSC_PER_HZ;
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/* advance the kernel's time tracking system */
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profile_tick(CPU_PROFILING);
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do_timer(1);
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}
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write_sequnlock(&xtime_lock);
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update_process_times(user_mode(get_irq_regs()));
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return IRQ_HANDLED;
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}
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/*
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* initialise the various timers used by the main part of the kernel
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*/
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void __init time_init(void)
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{
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/* we need the prescalar running to be able to use IOCLK/8
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* - IOCLK runs at 1/4 (ST5 open) or 1/8 (ST5 closed) internal CPU clock
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* - IOCLK runs at Fosc rate (crystal speed)
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*/
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TMPSCNT |= TMPSCNT_ENABLE;
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startup_timestamp_counter();
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printk(KERN_INFO
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"timestamp counter I/O clock running at %lu.%02lu"
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" (calibrated against RTC)\n",
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MN10300_TSCCLK / 1000000, (MN10300_TSCCLK / 10000) % 100);
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mn10300_last_tsc = TMTSCBC;
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/* use timer 0 & 1 cascaded to tick at as close to HZ as possible */
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setup_irq(TMJCIRQ, &timer_irq);
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set_intr_level(TMJCIRQ, TMJCICR_LEVEL);
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startup_jiffies_counter();
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#ifdef CONFIG_MN10300_WD_TIMER
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/* start the watchdog timer */
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watchdog_go();
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#endif
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mn10300_sched_clock_init();
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}
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