diff options
Diffstat (limited to 'drivers/clocksource/timer-atmel-st.c')
| -rw-r--r-- | drivers/clocksource/timer-atmel-st.c | 224 |
1 files changed, 224 insertions, 0 deletions
diff --git a/drivers/clocksource/timer-atmel-st.c b/drivers/clocksource/timer-atmel-st.c new file mode 100644 index 000000000000..1692e17e096b --- /dev/null +++ b/drivers/clocksource/timer-atmel-st.c @@ -0,0 +1,224 @@ +/* + * linux/arch/arm/mach-at91/at91rm9200_time.c + * + * Copyright (C) 2003 SAN People + * Copyright (C) 2003 ATMEL + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include <linux/kernel.h> +#include <linux/interrupt.h> +#include <linux/irq.h> +#include <linux/clockchips.h> +#include <linux/export.h> +#include <linux/mfd/syscon.h> +#include <linux/mfd/syscon/atmel-st.h> +#include <linux/of_irq.h> +#include <linux/regmap.h> + +static unsigned long last_crtr; +static u32 irqmask; +static struct clock_event_device clkevt; +static struct regmap *regmap_st; + +#define AT91_SLOW_CLOCK 32768 +#define RM9200_TIMER_LATCH ((AT91_SLOW_CLOCK + HZ/2) / HZ) + +/* + * 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) +{ + unsigned int x1, x2; + + regmap_read(regmap_st, AT91_ST_CRTR, &x1); + do { + regmap_read(regmap_st, AT91_ST_CRTR, &x2); + if (x1 == x2) + break; + x1 = x2; + } while (1); + return x1; +} + +/* + * IRQ handler for the timer. + */ +static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id) +{ + u32 sr; + + regmap_read(regmap_st, AT91_ST_SR, &sr); + sr &= irqmask; + + /* + * irqs should be disabled here, but as the irq is shared they are only + * guaranteed to be off if the timer irq is registered first. + */ + WARN_ON_ONCE(!irqs_disabled()); + + /* simulate "oneshot" timer with alarm */ + if (sr & AT91_ST_ALMS) { + clkevt.event_handler(&clkevt); + return IRQ_HANDLED; + } + + /* periodic mode should handle delayed ticks */ + if (sr & AT91_ST_PITS) { + u32 crtr = read_CRTR(); + + while (((crtr - last_crtr) & AT91_ST_CRTV) >= RM9200_TIMER_LATCH) { + last_crtr += RM9200_TIMER_LATCH; + clkevt.event_handler(&clkevt); + } + return IRQ_HANDLED; + } + + /* this irq is shared ... */ + return IRQ_NONE; +} + +static cycle_t read_clk32k(struct clocksource *cs) +{ + return read_CRTR(); +} + +static struct clocksource clk32k = { + .name = "32k_counter", + .rating = 150, + .read = read_clk32k, + .mask = CLOCKSOURCE_MASK(20), + .flags = CLOCK_SOURCE_IS_CONTINUOUS, +}; + +static void +clkevt32k_mode(enum clock_event_mode mode, struct clock_event_device *dev) +{ + unsigned int val; + + /* Disable and flush pending timer interrupts */ + regmap_write(regmap_st, AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS); + regmap_read(regmap_st, AT91_ST_SR, &val); + + last_crtr = read_CRTR(); + switch (mode) { + case CLOCK_EVT_MODE_PERIODIC: + /* PIT for periodic irqs; fixed rate of 1/HZ */ + irqmask = AT91_ST_PITS; + regmap_write(regmap_st, AT91_ST_PIMR, RM9200_TIMER_LATCH); + break; + case CLOCK_EVT_MODE_ONESHOT: + /* ALM for oneshot irqs, set by next_event() + * before 32 seconds have passed + */ + irqmask = AT91_ST_ALMS; + regmap_write(regmap_st, AT91_ST_RTAR, last_crtr); + break; + case CLOCK_EVT_MODE_SHUTDOWN: + case CLOCK_EVT_MODE_UNUSED: + case CLOCK_EVT_MODE_RESUME: + irqmask = 0; + break; + } + regmap_write(regmap_st, AT91_ST_IER, irqmask); +} + +static int +clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev) +{ + u32 alm; + int status = 0; + unsigned int val; + + BUG_ON(delta < 2); + + /* 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 */ + regmap_write(regmap_st, AT91_ST_RTAR, alm); + regmap_read(regmap_st, AT91_ST_SR, &val); + + /* Schedule alarm by writing RTAR. */ + alm += delta; + regmap_write(regmap_st, AT91_ST_RTAR, alm); + + return status; +} + +static struct clock_event_device clkevt = { + .name = "at91_tick", + .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, + .rating = 150, + .set_next_event = clkevt32k_next_event, + .set_mode = clkevt32k_mode, +}; + +/* + * ST (system timer) module supports both clockevents and clocksource. + */ +static void __init atmel_st_timer_init(struct device_node *node) +{ + unsigned int val; + int irq, ret; + + regmap_st = syscon_node_to_regmap(node); + if (IS_ERR(regmap_st)) + panic(pr_fmt("Unable to get regmap\n")); + + /* Disable all timer interrupts, and clear any pending ones */ + regmap_write(regmap_st, AT91_ST_IDR, + AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS); + regmap_read(regmap_st, AT91_ST_SR, &val); + + /* Get the interrupts property */ + irq = irq_of_parse_and_map(node, 0); + if (!irq) + panic(pr_fmt("Unable to get IRQ from DT\n")); + + /* Make IRQs happen for the system timer */ + ret = request_irq(irq, at91rm9200_timer_interrupt, + IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL, + "at91_tick", regmap_st); + if (ret) + panic(pr_fmt("Unable to setup IRQ\n")); + + /* 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. + */ + regmap_write(regmap_st, AT91_ST_RTMR, 1); + + /* Setup timer clockevent, with minimum of two ticks (important!!) */ + clkevt.cpumask = cpumask_of(0); + clockevents_config_and_register(&clkevt, AT91_SLOW_CLOCK, + 2, AT91_ST_ALMV); + + /* register clocksource */ + clocksource_register_hz(&clk32k, AT91_SLOW_CLOCK); +} +CLOCKSOURCE_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st", + atmel_st_timer_init); |