Commit a399e3fa authored by Nicolas Pitre's avatar Nicolas Pitre
Browse files

[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: default avatarNicolas Pitre <nico@marvell.com>
parent 8a3269fc

arch/arm/plat-orion/time.c

+32 −12
Original line number Diff line number Diff line
@@ -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 = 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 = NSEC_PER_SEC;

	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.)

	 */

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