diff options
| author | Nicolas Pitre <nico@cam.org> | 2009-05-15 00:42:36 -0400 |
|---|---|---|
| committer | Nicolas Pitre <nico@cam.org> | 2009-06-08 13:04:54 -0400 |
| commit | a399e3fa795afa058e4485b25c498e0c5a860428 (patch) | |
| tree | ce58f69f27ff8dc3b188f7e66dff9c19910d3646 /arch/arm/plat-orion | |
| parent | 8a3269fc21cc4405d80b362139c078cf655a505a (diff) | |
[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>
Diffstat (limited to 'arch/arm/plat-orion')
| -rw-r--r-- | arch/arm/plat-orion/time.c | 44 |
1 files changed, 32 insertions, 12 deletions
diff --git a/arch/arm/plat-orion/time.c b/arch/arm/plat-orion/time.c index b856cec8170..715a30177f2 100644 --- a/arch/arm/plat-orion/time.c +++ b/arch/arm/plat-orion/time.c @@ -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.) */ |