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authorNicolas Pitre <nico@cam.org>2009-05-15 00:42:36 -0400
committerNicolas Pitre <nico@cam.org>2009-06-08 13:04:54 -0400
commita399e3fa795afa058e4485b25c498e0c5a860428 (patch)
treece58f69f27ff8dc3b188f7e66dff9c19910d3646 /arch/arm
parent8a3269fc21cc4405d80b362139c078cf655a505a (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')
-rw-r--r--arch/arm/plat-orion/time.c44
1 files changed, 32 insertions, 12 deletions
diff --git a/arch/arm/plat-orion/time.c b/arch/arm/plat-orion/time.c
index b856cec81702..715a30177f28 100644
--- a/arch/arm/plat-orion/time.c
+++ b/arch/arm/plat-orion/time.c
@@ -12,14 +12,15 @@
12 */ 12 */
13 13
14#include <linux/kernel.h> 14#include <linux/kernel.h>
15#include <linux/sched.h>
16#include <linux/cnt32_to_63.h>
17#include <linux/timer.h>
15#include <linux/clockchips.h> 18#include <linux/clockchips.h>
16#include <linux/interrupt.h> 19#include <linux/interrupt.h>
17#include <linux/irq.h> 20#include <linux/irq.h>
18#include <asm/mach/time.h> 21#include <asm/mach/time.h>
19#include <mach/bridge-regs.h> 22#include <mach/bridge-regs.h>
20#include <mach/hardware.h> 23#include <mach/hardware.h>
21#include <linux/sched.h>
22#include <linux/cnt32_to_63.h>
23 24
24/* 25/*
25 * Number of timer ticks per jiffy. 26 * Number of timer ticks per jiffy.
@@ -44,14 +45,36 @@ static u32 ticks_per_jiffy;
44/* 45/*
45 * Orion's sched_clock implementation. It has a resolution of 46 * Orion's sched_clock implementation. It has a resolution of
46 * at least 7.5ns (133MHz TCLK) and a maximum value of 834 days. 47 * at least 7.5ns (133MHz TCLK) and a maximum value of 834 days.
48 *
49 * Because the hardware timer period is quite short (21 secs if
50 * 200MHz TCLK) and because cnt32_to_63() needs to be called at
51 * least once per half period to work properly, a kernel timer is
52 * set up to ensure this requirement is always met.
47 */ 53 */
48#define TCLK2NS_SCALE_FACTOR 8 54#define TCLK2NS_SCALE_FACTOR 8
49 55
50static unsigned long tclk2ns_scale; 56static unsigned long tclk2ns_scale;
51 57
52static void __init set_tclk2ns_scale(unsigned long tclk) 58unsigned long long sched_clock(void)
59{
60 unsigned long long v = cnt32_to_63(0xffffffff - readl(TIMER0_VAL));
61 return (v * tclk2ns_scale) >> TCLK2NS_SCALE_FACTOR;
62}
63
64static struct timer_list cnt32_to_63_keepwarm_timer;
65
66static void cnt32_to_63_keepwarm(unsigned long data)
67{
68 mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
69 (void) sched_clock();
70}
71
72static void __init setup_sched_clock(unsigned long tclk)
53{ 73{
54 unsigned long long v = NSEC_PER_SEC; 74 unsigned long long v;
75 unsigned long data;
76
77 v = NSEC_PER_SEC;
55 v <<= TCLK2NS_SCALE_FACTOR; 78 v <<= TCLK2NS_SCALE_FACTOR;
56 v += tclk/2; 79 v += tclk/2;
57 do_div(v, tclk); 80 do_div(v, tclk);
@@ -63,12 +86,10 @@ static void __init set_tclk2ns_scale(unsigned long tclk)
63 if (v & 1) 86 if (v & 1)
64 v++; 87 v++;
65 tclk2ns_scale = v; 88 tclk2ns_scale = v;
66}
67 89
68unsigned long long sched_clock(void) 90 data = (0xffffffffUL / tclk / 2 - 2) * HZ;
69{ 91 setup_timer(&cnt32_to_63_keepwarm_timer, cnt32_to_63_keepwarm, data);
70 unsigned long long v = cnt32_to_63(0xffffffff - readl(TIMER0_VAL)); 92 mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
71 return (v * tclk2ns_scale) >> TCLK2NS_SCALE_FACTOR;
72} 93}
73 94
74/* 95/*
@@ -210,9 +231,9 @@ void __init orion_time_init(unsigned int irq, unsigned int tclk)
210 ticks_per_jiffy = (tclk + HZ/2) / HZ; 231 ticks_per_jiffy = (tclk + HZ/2) / HZ;
211 232
212 /* 233 /*
213 * Set scale for sched_clock 234 * Set scale and timer for sched_clock
214 */ 235 */
215 set_tclk2ns_scale(tclk); 236 setup_sched_clock(tclk);
216 237
217 /* 238 /*
218 * Setup free-running clocksource timer (interrupts 239 * Setup free-running clocksource timer (interrupts
@@ -227,7 +248,6 @@ void __init orion_time_init(unsigned int irq, unsigned int tclk)
227 orion_clksrc.mult = clocksource_hz2mult(tclk, orion_clksrc.shift); 248 orion_clksrc.mult = clocksource_hz2mult(tclk, orion_clksrc.shift);
228 clocksource_register(&orion_clksrc); 249 clocksource_register(&orion_clksrc);
229 250
230
231 /* 251 /*
232 * Setup clockevent timer (interrupt-driven.) 252 * Setup clockevent timer (interrupt-driven.)
233 */ 253 */