diff options
Diffstat (limited to 'arch/arm/mach-at91')
| -rw-r--r-- | arch/arm/mach-at91/Kconfig | 2 | ||||
| -rw-r--r-- | arch/arm/mach-at91/at91rm9200_time.c | 195 |
2 files changed, 132 insertions, 65 deletions
diff --git a/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig index fd956f1299d..05a9f8a1b45 100644 --- a/arch/arm/mach-at91/Kconfig +++ b/arch/arm/mach-at91/Kconfig @@ -7,6 +7,8 @@ choice config ARCH_AT91RM9200 bool "AT91RM9200" + select GENERIC_TIME + select GENERIC_CLOCKEVENTS config ARCH_AT91SAM9260 bool "AT91SAM9260 or AT91SAM9XE" diff --git a/arch/arm/mach-at91/at91rm9200_time.c b/arch/arm/mach-at91/at91rm9200_time.c index a6340357585..50392ff7151 100644 --- a/arch/arm/mach-at91/at91rm9200_time.c +++ b/arch/arm/mach-at91/at91rm9200_time.c @@ -19,70 +19,64 @@ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ -#include <linux/init.h> +#include <linux/kernel.h> #include <linux/interrupt.h> #include <linux/irq.h> -#include <linux/kernel.h> -#include <linux/sched.h> -#include <linux/time.h> +#include <linux/clockchips.h> -#include <asm/hardware.h> -#include <asm/io.h> #include <asm/mach/time.h> #include <asm/arch/at91_st.h> static unsigned long last_crtr; +static u32 irqmask; +static struct clock_event_device clkevt; /* - * The ST_CRTR is updated asynchronously to the master clock. It is therefore - * necessary to read it twice (with the same value) to ensure accuracy. + * The ST_CRTR is updated asynchronously to the master clock ... but + * the updates as seen by the CPU don't seem to be strictly monotonic. + * Waiting until we read the same value twice avoids glitching. */ -static inline unsigned long read_CRTR(void) { +static inline unsigned long read_CRTR(void) +{ unsigned long x1, x2; + x1 = at91_sys_read(AT91_ST_CRTR); do { - x1 = at91_sys_read(AT91_ST_CRTR); x2 = at91_sys_read(AT91_ST_CRTR); - } while (x1 != x2); - + if (x1 == x2) + break; + x1 = x2; + } while (1); return x1; } /* - * Returns number of microseconds since last timer interrupt. Note that interrupts - * will have been disabled by do_gettimeofday() - * 'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy. - * 'tick' is usecs per jiffy (linux/timex.h). - */ -static unsigned long at91rm9200_gettimeoffset(void) -{ - unsigned long elapsed; - - elapsed = (read_CRTR() - last_crtr) & AT91_ST_ALMV; - - return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH; -} - -/* * IRQ handler for the timer. */ static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id) { - if (at91_sys_read(AT91_ST_SR) & AT91_ST_PITS) { /* This is a shared interrupt */ - write_seqlock(&xtime_lock); + u32 sr = at91_sys_read(AT91_ST_SR) & irqmask; - while (((read_CRTR() - last_crtr) & AT91_ST_ALMV) >= LATCH) { - timer_tick(); - last_crtr = (last_crtr + LATCH) & AT91_ST_ALMV; - } + /* simulate "oneshot" timer with alarm */ + if (sr & AT91_ST_ALMS) { + clkevt.event_handler(&clkevt); + return IRQ_HANDLED; + } - write_sequnlock(&xtime_lock); + /* periodic mode should handle delayed ticks */ + if (sr & AT91_ST_PITS) { + u32 crtr = read_CRTR(); + while (((crtr - last_crtr) & AT91_ST_CRTV) >= LATCH) { + last_crtr += LATCH; + clkevt.event_handler(&clkevt); + } return IRQ_HANDLED; } - else - return IRQ_NONE; /* not handled */ + + /* this irq is shared ... */ + return IRQ_NONE; } static struct irqaction at91rm9200_timer_irq = { @@ -91,56 +85,127 @@ static struct irqaction at91rm9200_timer_irq = { .handler = at91rm9200_timer_interrupt }; -void at91rm9200_timer_reset(void) +static cycle_t read_clk32k(void) { - last_crtr = 0; + return read_CRTR(); +} - /* Real time counter incremented every 30.51758 microseconds */ - at91_sys_write(AT91_ST_RTMR, 1); +static struct clocksource clk32k = { + .name = "32k_counter", + .rating = 150, + .read = read_clk32k, + .mask = CLOCKSOURCE_MASK(20), + .shift = 10, + .flags = CLOCK_SOURCE_IS_CONTINUOUS, +}; + +static void +clkevt32k_mode(enum clock_event_mode mode, struct clock_event_device *dev) +{ + /* Disable and flush pending timer interrupts */ + at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS); + (void) at91_sys_read(AT91_ST_SR); - /* Set Period Interval timer */ - at91_sys_write(AT91_ST_PIMR, LATCH); + last_crtr = read_CRTR(); + switch (mode) { + case CLOCK_EVT_MODE_PERIODIC: + /* PIT for periodic irqs; fixed rate of 1/HZ */ + irqmask = AT91_ST_PITS; + at91_sys_write(AT91_ST_PIMR, LATCH); + break; + case CLOCK_EVT_MODE_ONESHOT: + /* ALM for oneshot irqs, set by next_event() + * before 32 seconds have passed + */ + irqmask = AT91_ST_ALMS; + at91_sys_write(AT91_ST_RTAR, last_crtr); + break; + case CLOCK_EVT_MODE_SHUTDOWN: + case CLOCK_EVT_MODE_UNUSED: + case CLOCK_EVT_MODE_RESUME: + irqmask = 0; + break; + } + at91_sys_write(AT91_ST_IER, irqmask); +} - /* Clear any pending interrupts */ +static int +clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev) +{ + unsigned long flags; + u32 alm; + int status = 0; + + BUG_ON(delta < 2); + + /* Use "raw" primitives so we behave correctly on RT kernels. */ + raw_local_irq_save(flags); + + /* The alarm IRQ uses absolute time (now+delta), not the relative + * time (delta) in our calling convention. Like all clockevents + * using such "match" hardware, we have a race to defend against. + * + * Our defense here is to have set up the clockevent device so the + * delta is at least two. That way we never end up writing RTAR + * with the value then held in CRTR ... which would mean the match + * wouldn't trigger until 32 seconds later, after CRTR wraps. + */ + alm = read_CRTR(); + + /* Cancel any pending alarm; flush any pending IRQ */ + at91_sys_write(AT91_ST_RTAR, alm); (void) at91_sys_read(AT91_ST_SR); - /* Enable Period Interval Timer interrupt */ - at91_sys_write(AT91_ST_IER, AT91_ST_PITS); + /* Schedule alarm by writing RTAR. */ + alm += delta; + at91_sys_write(AT91_ST_RTAR, alm); + + raw_local_irq_restore(flags); + return status; } +static struct clock_event_device clkevt = { + .name = "at91_tick", + .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, + .shift = 32, + .rating = 150, + .cpumask = CPU_MASK_CPU0, + .set_next_event = clkevt32k_next_event, + .set_mode = clkevt32k_mode, +}; + /* - * Set up timer interrupt. + * ST (system timer) module supports both clockevents and clocksource. */ void __init at91rm9200_timer_init(void) { - /* Disable all timer interrupts */ - at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS); - (void) at91_sys_read(AT91_ST_SR); /* Clear any pending interrupts */ + /* Disable all timer interrupts, and clear any pending ones */ + at91_sys_write(AT91_ST_IDR, + AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS); + (void) at91_sys_read(AT91_ST_SR); /* Make IRQs happen for the system timer */ setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq); - /* Change the kernel's 'tick' value to 10009 usec. (the default is 10000) */ - tick_usec = (LATCH * 1000000) / CLOCK_TICK_RATE; + /* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used + * directly for the clocksource and all clockevents, after adjusting + * its prescaler from the 1 Hz default. + */ + at91_sys_write(AT91_ST_RTMR, 1); - /* Initialize and enable the timer interrupt */ - at91rm9200_timer_reset(); -} + /* Setup timer clockevent, with minimum of two ticks (important!!) */ + clkevt.mult = div_sc(AT91_SLOW_CLOCK, NSEC_PER_SEC, clkevt.shift); + clkevt.max_delta_ns = clockevent_delta2ns(AT91_ST_ALMV, &clkevt); + clkevt.min_delta_ns = clockevent_delta2ns(2, &clkevt) + 1; + clkevt.cpumask = cpumask_of_cpu(0); + clockevents_register_device(&clkevt); -#ifdef CONFIG_PM -static void at91rm9200_timer_suspend(void) -{ - /* disable Period Interval Timer interrupt */ - at91_sys_write(AT91_ST_IDR, AT91_ST_PITS); + /* register clocksource */ + clk32k.mult = clocksource_hz2mult(AT91_SLOW_CLOCK, clk32k.shift); + clocksource_register(&clk32k); } -#else -#define at91rm9200_timer_suspend NULL -#endif struct sys_timer at91rm9200_timer = { .init = at91rm9200_timer_init, - .offset = at91rm9200_gettimeoffset, - .suspend = at91rm9200_timer_suspend, - .resume = at91rm9200_timer_reset, }; |