diff options
Diffstat (limited to 'arch/blackfin/kernel/time-ts.c')
| -rw-r--r-- | arch/blackfin/kernel/time-ts.c | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/arch/blackfin/kernel/time-ts.c b/arch/blackfin/kernel/time-ts.c index 1ce8cb1e4982..4482c47c09e5 100644 --- a/arch/blackfin/kernel/time-ts.c +++ b/arch/blackfin/kernel/time-ts.c @@ -16,11 +16,35 @@ #include <linux/irq.h> #include <linux/clocksource.h> #include <linux/clockchips.h> +#include <linux/cpufreq.h> #include <asm/blackfin.h> +#include <asm/time.h> #ifdef CONFIG_CYCLES_CLOCKSOURCE +/* Accelerators for sched_clock() + * convert from cycles(64bits) => nanoseconds (64bits) + * basic equation: + * ns = cycles / (freq / ns_per_sec) + * ns = cycles * (ns_per_sec / freq) + * ns = cycles * (10^9 / (cpu_khz * 10^3)) + * ns = cycles * (10^6 / cpu_khz) + * + * Then we use scaling math (suggested by george@mvista.com) to get: + * ns = cycles * (10^6 * SC / cpu_khz) / SC + * ns = cycles * cyc2ns_scale / SC + * + * And since SC is a constant power of two, we can convert the div + * into a shift. + * + * We can use khz divisor instead of mhz to keep a better precision, since + * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits. + * (mathieu.desnoyers@polymtl.ca) + * + * -johnstul@us.ibm.com "math is hard, lets go shopping!" + */ + static unsigned long cyc2ns_scale; #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */ @@ -82,8 +106,9 @@ static void bfin_timer_set_mode(enum clock_event_mode mode, { switch (mode) { case CLOCK_EVT_MODE_PERIODIC: { - unsigned long tcount = ((get_cclk() / (HZ * 1)) - 1); + unsigned long tcount = ((get_cclk() / (HZ * TIME_SCALE)) - 1); bfin_write_TCNTL(TMPWR); + bfin_write_TSCALE(TIME_SCALE - 1); CSYNC(); bfin_write_TPERIOD(tcount); bfin_write_TCOUNT(tcount); @@ -92,6 +117,7 @@ static void bfin_timer_set_mode(enum clock_event_mode mode, break; } case CLOCK_EVT_MODE_ONESHOT: + bfin_write_TSCALE(0); bfin_write_TCOUNT(0); bfin_write_TCNTL(TMPWR | TMREN); CSYNC(); @@ -115,7 +141,7 @@ static void __init bfin_timer_init(void) /* * the TSCALE prescaler counter. */ - bfin_write_TSCALE(0); + bfin_write_TSCALE(TIME_SCALE - 1); bfin_write_TPERIOD(0); bfin_write_TCOUNT(0); |