diff options
| -rw-r--r-- | arch/arm/plat-nomadik/timer.c | 89 |
1 files changed, 80 insertions, 9 deletions
diff --git a/arch/arm/plat-nomadik/timer.c b/arch/arm/plat-nomadik/timer.c index aedf9c1..63cdc60 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); |