1 files changed, 80 insertions, 9 deletions

diff --git a/arch/arm/plat-nomadik/timer.c b/arch/arm/plat-nomadik/timer.c
index aedf9c1d645e..63cdc6025bd7 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);