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[ARM] orion: make sure sched_clock() usage of cnt32_to_63() is safe 

With a TCLK = 200MHz, the half period of the hardware timer is roughly
10 seconds. Because cnt32_to_63() must be called at least once per
half period of the base hardware counter, it is a bit risky to rely
solely on scheduling to generate frequent enough calls. Let's use a
kernel timer to ensure this.

Signed-off-by: Nicolas Pitre <nico@marvell.com>
This commit is contained in:
Nicolas Pitre 2009-05-15 00:42:36 -04:00
parent 8a3269fc21
commit a399e3fa79
1 changed files with 32 additions and 12 deletions
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44
arch/arm/plat-orion/time.c
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@ -12,14 +12,15 @@
*/
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/cnt32_to_63.h>
#include <linux/timer.h>
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <asm/mach/time.h>
#include <mach/bridge-regs.h>
#include <mach/hardware.h>
#include <linux/sched.h>
#include <linux/cnt32_to_63.h>
/*
* Number of timer ticks per jiffy.
@ -44,14 +45,36 @@ static u32 ticks_per_jiffy;
/*
* Orion's sched_clock implementation. It has a resolution of
* at least 7.5ns (133MHz TCLK) and a maximum value of 834 days.
*
* Because the hardware timer period is quite short (21 secs if
* 200MHz TCLK) and because cnt32_to_63() needs to be called at
* least once per half period to work properly, a kernel timer is
* set up to ensure this requirement is always met.
*/
#define TCLK2NS_SCALE_FACTOR 8
static unsigned long tclk2ns_scale;
static void __init set_tclk2ns_scale(unsigned long tclk)
unsigned long long sched_clock(void)
{
unsigned long long v = NSEC_PER_SEC;
unsigned long long v = cnt32_to_63(0xffffffff - readl(TIMER0_VAL));
return (v * tclk2ns_scale) >> TCLK2NS_SCALE_FACTOR;
}
static struct timer_list cnt32_to_63_keepwarm_timer;
static void cnt32_to_63_keepwarm(unsigned long data)
{
mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
(void) sched_clock();
}
static void __init setup_sched_clock(unsigned long tclk)
{
unsigned long long v;
unsigned long data;
v = NSEC_PER_SEC;
v <<= TCLK2NS_SCALE_FACTOR;
v += tclk/2;
do_div(v, tclk);
@ -63,12 +86,10 @@ static void __init set_tclk2ns_scale(unsigned long tclk)
if (v & 1)
v++;
tclk2ns_scale = v;
}
unsigned long long sched_clock(void)
{
unsigned long long v = cnt32_to_63(0xffffffff - readl(TIMER0_VAL));
return (v * tclk2ns_scale) >> TCLK2NS_SCALE_FACTOR;
data = (0xffffffffUL / tclk / 2 - 2) * HZ;
setup_timer(&cnt32_to_63_keepwarm_timer, cnt32_to_63_keepwarm, data);
mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
}
/*
@ -210,9 +231,9 @@ void __init orion_time_init(unsigned int irq, unsigned int tclk)
ticks_per_jiffy = (tclk + HZ/2) / HZ;
/*
* Set scale for sched_clock
* Set scale and timer for sched_clock
*/
set_tclk2ns_scale(tclk);
setup_sched_clock(tclk);
/*
* Setup free-running clocksource timer (interrupts
@ -227,7 +248,6 @@ void __init orion_time_init(unsigned int irq, unsigned int tclk)
orion_clksrc.mult = clocksource_hz2mult(tclk, orion_clksrc.shift);
clocksource_register(&orion_clksrc);
/*
* Setup clockevent timer (interrupt-driven.)
*/