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https://github.com/torvalds/linux
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a44c1d700c
Replace the old gettimeoffset() interface (which became buggy in several ways) with a clocksource that atomically reads the count and status from the timer, and corrects the count as appropriate ensuring proper resolution of time without time warping backwards. We keep the original periodic timer non-clock event implementation to provide the kernel with a regular source of interrupts, which are required to keep the clocksource properly updated. Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
105 lines
2.4 KiB
C
105 lines
2.4 KiB
C
/*
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* linux/arch/arm/common/time-acorn.c
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*
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* Copyright (c) 1996-2000 Russell King.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* Changelog:
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* 24-Sep-1996 RMK Created
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* 10-Oct-1996 RMK Brought up to date with arch-sa110eval
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* 04-Dec-1997 RMK Updated for new arch/arm/time.c
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* 13=Jun-2004 DS Moved to arch/arm/common b/c shared w/CLPS7500
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*/
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#include <linux/clocksource.h>
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#include <linux/init.h>
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#include <linux/interrupt.h>
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#include <linux/irq.h>
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#include <linux/io.h>
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#include <mach/hardware.h>
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#include <asm/hardware/ioc.h>
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#include <asm/mach/time.h>
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#define RPC_CLOCK_FREQ 2000000
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#define RPC_LATCH DIV_ROUND_CLOSEST(RPC_CLOCK_FREQ, HZ)
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static u32 ioc_time;
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static u64 ioc_timer_read(struct clocksource *cs)
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{
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unsigned int count1, count2, status;
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unsigned long flags;
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u32 ticks;
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local_irq_save(flags);
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ioc_writeb (0, IOC_T0LATCH);
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barrier ();
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count1 = ioc_readb(IOC_T0CNTL) | (ioc_readb(IOC_T0CNTH) << 8);
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barrier ();
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status = ioc_readb(IOC_IRQREQA);
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barrier ();
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ioc_writeb (0, IOC_T0LATCH);
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barrier ();
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count2 = ioc_readb(IOC_T0CNTL) | (ioc_readb(IOC_T0CNTH) << 8);
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ticks = ioc_time + RPC_LATCH - count2;
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local_irq_restore(flags);
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if (count2 < count1) {
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/*
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* The timer has not reloaded between reading count1 and
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* count2, check whether an interrupt was actually pending.
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*/
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if (status & (1 << 5))
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ticks += RPC_LATCH;
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} else if (count2 > count1) {
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/*
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* The timer has reloaded, so count2 indicates the new
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* count since the wrap. The interrupt would not have
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* been processed, so add the missed ticks.
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*/
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ticks += RPC_LATCH;
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}
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return ticks;
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}
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static struct clocksource ioctime_clocksource = {
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.read = ioc_timer_read,
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.mask = CLOCKSOURCE_MASK(32),
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.rating = 100,
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};
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void __init ioctime_init(void)
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{
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ioc_writeb(RPC_LATCH & 255, IOC_T0LTCHL);
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ioc_writeb(RPC_LATCH >> 8, IOC_T0LTCHH);
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ioc_writeb(0, IOC_T0GO);
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}
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static irqreturn_t
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ioc_timer_interrupt(int irq, void *dev_id)
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{
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ioc_time += RPC_LATCH;
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timer_tick();
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return IRQ_HANDLED;
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}
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static struct irqaction ioc_timer_irq = {
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.name = "timer",
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.handler = ioc_timer_interrupt
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};
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/*
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* Set up timer interrupt.
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*/
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void __init ioc_timer_init(void)
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{
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WARN_ON(clocksource_register_hz(&ioctime_clocksource, RPC_CLOCK_FREQ));
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ioctime_init();
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setup_irq(IRQ_TIMER0, &ioc_timer_irq);
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}
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