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39806805de
Patch from Andrew Victor
If the timer interrupt is ever significantly delayed (or after the
system was suspended), the system could spin incrementing the time for
too long.
The fix is to replace the "do {} while" with a "while {}".
Orignal patch by Savin Zlobec and Peter Menzebach.
Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
127 lines
3.5 KiB
C
127 lines
3.5 KiB
C
/*
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* linux/arch/arm/mach-at91rm9200/time.c
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*
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* Copyright (C) 2003 SAN People
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* Copyright (C) 2003 ATMEL
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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 as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/config.h>
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#include <linux/init.h>
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#include <linux/interrupt.h>
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/time.h>
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#include <asm/hardware.h>
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#include <asm/io.h>
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#include <asm/irq.h>
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#include <asm/mach/time.h>
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/*
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* The ST_CRTR is updated asynchronously to the master clock. It is therefore
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* necessary to read it twice (with the same value) to ensure accuracy.
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*/
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static inline unsigned long read_CRTR(void) {
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unsigned long x1, x2;
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do {
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x1 = at91_sys_read(AT91_ST_CRTR);
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x2 = at91_sys_read(AT91_ST_CRTR);
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} while (x1 != x2);
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return x1;
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}
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/*
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* Returns number of microseconds since last timer interrupt. Note that interrupts
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* will have been disabled by do_gettimeofday()
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* 'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy.
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* 'tick' is usecs per jiffy (linux/timex.h).
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*/
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static unsigned long at91rm9200_gettimeoffset(void)
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{
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unsigned long elapsed;
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elapsed = (read_CRTR() - at91_sys_read(AT91_ST_RTAR)) & AT91_ST_ALMV;
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return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH;
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}
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/*
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* IRQ handler for the timer.
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*/
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static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
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{
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unsigned long rtar;
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if (at91_sys_read(AT91_ST_SR) & AT91_ST_PITS) { /* This is a shared interrupt */
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write_seqlock(&xtime_lock);
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while (((read_CRTR() - at91_sys_read(AT91_ST_RTAR)) & AT91_ST_ALMV) >= LATCH) {
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timer_tick(regs);
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rtar = (at91_sys_read(AT91_ST_RTAR) + LATCH) & AT91_ST_ALMV;
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at91_sys_write(AT91_ST_RTAR, rtar);
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}
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write_sequnlock(&xtime_lock);
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return IRQ_HANDLED;
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}
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else
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return IRQ_NONE; /* not handled */
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}
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static struct irqaction at91rm9200_timer_irq = {
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.name = "at91_tick",
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.flags = SA_SHIRQ | SA_INTERRUPT,
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.handler = at91rm9200_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 at91rm9200_timer_init(void)
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{
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/* Disable all timer interrupts */
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at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
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(void) at91_sys_read(AT91_ST_SR); /* Clear any pending interrupts */
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/*
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* Make IRQs happen for the system timer.
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*/
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setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq);
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/* Set initial alarm to 0 */
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at91_sys_write(AT91_ST_RTAR, 0);
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/* Real time counter incremented every 30.51758 microseconds */
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at91_sys_write(AT91_ST_RTMR, 1);
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/* Set Period Interval timer */
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at91_sys_write(AT91_ST_PIMR, LATCH);
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/* Change the kernel's 'tick' value to 10009 usec. (the default is 10000) */
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tick_usec = (LATCH * 1000000) / CLOCK_TICK_RATE;
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/* Enable Period Interval Timer interrupt */
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at91_sys_write(AT91_ST_IER, AT91_ST_PITS);
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}
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struct sys_timer at91rm9200_timer = {
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.init = at91rm9200_timer_init,
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.offset = at91rm9200_gettimeoffset,
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};
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