[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>
diff --git a/arch/arm/plat-orion/time.c b/arch/arm/plat-orion/time.c
index b856cec..715a301 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 @@
/*
* 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 @@
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 @@
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 @@
orion_clksrc.mult = clocksource_hz2mult(tclk, orion_clksrc.shift);
clocksource_register(&orion_clksrc);
-
/*
* Setup clockevent timer (interrupt-driven.)
*/