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authorLinus Walleij <linus.walleij@stericsson.com>2010-11-19 10:16:05 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-11-21 22:05:57 +0000
commit8fbb97a2bc9b8c91b5a4588ba80709e48dad3f16 (patch)
tree7843b6acb76bf1b0679c78fdf3d45402eea8e86f
parent963fec4e0f4993486ee91edfafba0c972834d8c3 (diff)
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ARM: 6488/1: nomadik: prevent sched_clock() wraparound
The current implementation of sched_clock() for the Nomadik family is based on the clock source that will wrap around without any compensation. Currently on the Ux500 after 1030 seconds. Utilize cnt32_to_63 to expand the sched_clock() counter to 63 bits and introduce a keepwarm() timer to assure that sched clock and this cnt32_to_63 is called atleast once every half period. When I print out the actual wrap-around time, and using a year (3600*24*365 seconds) as minumum wrap limit I get an actual wrap-around of: sched_clock: using 55 bits @ 8333125 Hz wrap in 416 days Signed-off-by: Linus Walleij <linus.walleij@stericsson.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
-rw-r--r--arch/arm/plat-nomadik/timer.c89
1 files changed, 80 insertions, 9 deletions
diff --git a/arch/arm/plat-nomadik/timer.c b/arch/arm/plat-nomadik/timer.c
index aedf9c1d645..63cdc6025bd 100644
--- a/arch/arm/plat-nomadik/timer.c
+++ b/arch/arm/plat-nomadik/timer.c
@@ -3,6 +3,7 @@
*
* Copyright (C) 2008 STMicroelectronics
* Copyright (C) 2010 Alessandro Rubini
+ * Copyright (C) 2010 Linus Walleij for ST-Ericsson
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2, as
@@ -16,11 +17,13 @@
#include <linux/clk.h>
#include <linux/jiffies.h>
#include <linux/err.h>
+#include <linux/cnt32_to_63.h>
+#include <linux/timer.h>
#include <asm/mach/time.h>
#include <plat/mtu.h>
-void __iomem *mtu_base; /* ssigned by machine code */
+void __iomem *mtu_base; /* Assigned by machine code */
/*
* Kernel assumes that sched_clock can be called early
@@ -48,16 +51,82 @@ static struct clocksource nmdk_clksrc = {
/*
* Override the global weak sched_clock symbol with this
* local implementation which uses the clocksource to get some
- * better resolution when scheduling the kernel. We accept that
- * this wraps around for now, since it is just a relative time
- * stamp. (Inspired by OMAP implementation.)
+ * better resolution when scheduling the kernel.
+ *
+ * Because the hardware timer period may be quite short
+ * (32.3 secs on the 133 MHz MTU timer selection on ux500)
+ * and because cnt32_to_63() needs to be called at least once per
+ * half period to work properly, a kernel keepwarm() timer is set up
+ * to ensure this requirement is always met.
+ *
+ * Also the sched_clock timer will wrap around at some point,
+ * here we set it to run continously for a year.
*/
+#define SCHED_CLOCK_MIN_WRAP 3600*24*365
+static struct timer_list cnt32_to_63_keepwarm_timer;
+static u32 sched_mult;
+static u32 sched_shift;
+
unsigned long long notrace sched_clock(void)
{
- return clocksource_cyc2ns(nmdk_clksrc.read(
- &nmdk_clksrc),
- nmdk_clksrc.mult,
- nmdk_clksrc.shift);
+ u64 cycles;
+
+ if (unlikely(!mtu_base))
+ return 0;
+
+ cycles = cnt32_to_63(-readl(mtu_base + MTU_VAL(0)));
+ /*
+ * sched_mult is guaranteed to be even so will
+ * shift out bit 63
+ */
+ return (cycles * sched_mult) >> sched_shift;
+}
+
+/* Just kick sched_clock every so often */
+static void cnt32_to_63_keepwarm(unsigned long data)
+{
+ mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
+ (void) sched_clock();
+}
+
+/*
+ * Set up a timer to keep sched_clock():s 32_to_63 algorithm warm
+ * once in half a 32bit timer wrap interval.
+ */
+static void __init nmdk_sched_clock_init(unsigned long rate)
+{
+ u32 v;
+ unsigned long delta;
+ u64 days;
+
+ /* Find the apropriate mult and shift factors */
+ clocks_calc_mult_shift(&sched_mult, &sched_shift,
+ rate, NSEC_PER_SEC, SCHED_CLOCK_MIN_WRAP);
+ /* We need to multiply by an even number to get rid of bit 63 */
+ if (sched_mult & 1)
+ sched_mult++;
+
+ /* Let's see what we get, take max counter and scale it */
+ days = (0xFFFFFFFFFFFFFFFFLLU * sched_mult) >> sched_shift;
+ do_div(days, NSEC_PER_SEC);
+ do_div(days, (3600*24));
+
+ pr_info("sched_clock: using %d bits @ %lu Hz wrap in %lu days\n",
+ (64 - sched_shift), rate, (unsigned long) days);
+
+ /*
+ * Program a timer to kick us at half 32bit wraparound
+ * Formula: seconds per wrap = (2^32) / f
+ */
+ v = 0xFFFFFFFFUL / rate;
+ /* We want half of the wrap time to keep cnt32_to_63 warm */
+ v /= 2;
+ pr_debug("sched_clock: prescaled timer rate: %lu Hz, "
+ "initialize keepwarm timer every %d seconds\n", rate, v);
+ /* Convert seconds to jiffies */
+ delta = msecs_to_jiffies(v*1000);
+ setup_timer(&cnt32_to_63_keepwarm_timer, cnt32_to_63_keepwarm, delta);
+ mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + delta));
}
/* Clockevent device: use one-shot mode */
@@ -161,13 +230,15 @@ void __init nmdk_timer_init(void)
writel(0, mtu_base + MTU_BGLR(0));
writel(cr | MTU_CRn_ENA, mtu_base + MTU_CR(0));
- /* Now the scheduling clock is ready */
+ /* Now the clock source is ready */
nmdk_clksrc.read = nmdk_read_timer;
if (clocksource_register(&nmdk_clksrc))
pr_err("timer: failed to initialize clock source %s\n",
nmdk_clksrc.name);
+ nmdk_sched_clock_init(rate);
+
/* Timer 1 is used for events */
clockevents_calc_mult_shift(&nmdk_clkevt, rate, MTU_MIN_RANGE);