LXR linux/drivers/clocksource/timer-atmel-pit.c

   1/*
   2 * at91sam926x_time.c - Periodic Interval Timer (PIT) for at91sam926x
   3 *
   4 * Copyright (C) 2005-2006 M. Amine SAYA, ATMEL Rousset, France
   5 * Revision      2005 M. Nicolas Diremdjian, ATMEL Rousset, France
   6 * Converted to ClockSource/ClockEvents by David Brownell.
   7 *
   8 * This program is free software; you can redistribute it and/or modify
   9 * it under the terms of the GNU General Public License version 2 as
  10 * published by the Free Software Foundation.
  11 */
  12
  13#define pr_fmt(fmt)     "AT91: PIT: " fmt
  14
  15#include <linux/clk.h>
  16#include <linux/clockchips.h>
  17#include <linux/interrupt.h>
  18#include <linux/irq.h>
  19#include <linux/kernel.h>
  20#include <linux/of.h>
  21#include <linux/of_address.h>
  22#include <linux/of_irq.h>
  23#include <linux/slab.h>
  24
  25#define AT91_PIT_MR             0x00                    /* Mode Register */
  26#define AT91_PIT_PITIEN                 BIT(25)                 /* Timer Interrupt Enable */
  27#define AT91_PIT_PITEN                  BIT(24)                 /* Timer Enabled */
  28#define AT91_PIT_PIV                    GENMASK(19, 0)          /* Periodic Interval Value */
  29
  30#define AT91_PIT_SR             0x04                    /* Status Register */
  31#define AT91_PIT_PITS                   BIT(0)                  /* Timer Status */
  32
  33#define AT91_PIT_PIVR           0x08                    /* Periodic Interval Value Register */
  34#define AT91_PIT_PIIR           0x0c                    /* Periodic Interval Image Register */
  35#define AT91_PIT_PICNT                  GENMASK(31, 20)         /* Interval Counter */
  36#define AT91_PIT_CPIV                   GENMASK(19, 0)          /* Inverval Value */
  37
  38#define PIT_CPIV(x)     ((x) & AT91_PIT_CPIV)
  39#define PIT_PICNT(x)    (((x) & AT91_PIT_PICNT) >> 20)
  40
  41struct pit_data {
  42        struct clock_event_device       clkevt;
  43        struct clocksource              clksrc;
  44
  45        void __iomem    *base;
  46        u32             cycle;
  47        u32             cnt;
  48        unsigned int    irq;
  49        struct clk      *mck;
  50};
  51
  52static inline struct pit_data *clksrc_to_pit_data(struct clocksource *clksrc)
  53{
  54        return container_of(clksrc, struct pit_data, clksrc);
  55}
  56
  57static inline struct pit_data *clkevt_to_pit_data(struct clock_event_device *clkevt)
  58{
  59        return container_of(clkevt, struct pit_data, clkevt);
  60}
  61
  62static inline unsigned int pit_read(void __iomem *base, unsigned int reg_offset)
  63{
  64        return readl_relaxed(base + reg_offset);
  65}
  66
  67static inline void pit_write(void __iomem *base, unsigned int reg_offset, unsigned long value)
  68{
  69        writel_relaxed(value, base + reg_offset);
  70}
  71
  72/*
  73 * Clocksource:  just a monotonic counter of MCK/16 cycles.
  74 * We don't care whether or not PIT irqs are enabled.
  75 */
  76static cycle_t read_pit_clk(struct clocksource *cs)
  77{
  78        struct pit_data *data = clksrc_to_pit_data(cs);
  79        unsigned long flags;
  80        u32 elapsed;
  81        u32 t;
  82
  83        raw_local_irq_save(flags);
  84        elapsed = data->cnt;
  85        t = pit_read(data->base, AT91_PIT_PIIR);
  86        raw_local_irq_restore(flags);
  87
  88        elapsed += PIT_PICNT(t) * data->cycle;
  89        elapsed += PIT_CPIV(t);
  90        return elapsed;
  91}
  92
  93static int pit_clkevt_shutdown(struct clock_event_device *dev)
  94{
  95        struct pit_data *data = clkevt_to_pit_data(dev);
  96
  97        /* disable irq, leaving the clocksource active */
  98        pit_write(data->base, AT91_PIT_MR, (data->cycle - 1) | AT91_PIT_PITEN);
  99        return 0;
 100}
 101
 102/*
 103 * Clockevent device:  interrupts every 1/HZ (== pit_cycles * MCK/16)
 104 */
 105static int pit_clkevt_set_periodic(struct clock_event_device *dev)
 106{
 107        struct pit_data *data = clkevt_to_pit_data(dev);
 108
 109        /* update clocksource counter */
 110        data->cnt += data->cycle * PIT_PICNT(pit_read(data->base, AT91_PIT_PIVR));
 111        pit_write(data->base, AT91_PIT_MR,
 112                  (data->cycle - 1) | AT91_PIT_PITEN | AT91_PIT_PITIEN);
 113        return 0;
 114}
 115
 116static void at91sam926x_pit_suspend(struct clock_event_device *cedev)
 117{
 118        struct pit_data *data = clkevt_to_pit_data(cedev);
 119
 120        /* Disable timer */
 121        pit_write(data->base, AT91_PIT_MR, 0);
 122}
 123
 124static void at91sam926x_pit_reset(struct pit_data *data)
 125{
 126        /* Disable timer and irqs */
 127        pit_write(data->base, AT91_PIT_MR, 0);
 128
 129        /* Clear any pending interrupts, wait for PIT to stop counting */
 130        while (PIT_CPIV(pit_read(data->base, AT91_PIT_PIVR)) != 0)
 131                cpu_relax();
 132
 133        /* Start PIT but don't enable IRQ */
 134        pit_write(data->base, AT91_PIT_MR,
 135                  (data->cycle - 1) | AT91_PIT_PITEN);
 136}
 137
 138static void at91sam926x_pit_resume(struct clock_event_device *cedev)
 139{
 140        struct pit_data *data = clkevt_to_pit_data(cedev);
 141
 142        at91sam926x_pit_reset(data);
 143}
 144
 145/*
 146 * IRQ handler for the timer.
 147 */
 148static irqreturn_t at91sam926x_pit_interrupt(int irq, void *dev_id)
 149{
 150        struct pit_data *data = dev_id;
 151
 152        /*
 153         * irqs should be disabled here, but as the irq is shared they are only
 154         * guaranteed to be off if the timer irq is registered first.
 155         */
 156        WARN_ON_ONCE(!irqs_disabled());
 157
 158        /* The PIT interrupt may be disabled, and is shared */
 159        if (clockevent_state_periodic(&data->clkevt) &&
 160            (pit_read(data->base, AT91_PIT_SR) & AT91_PIT_PITS)) {
 161                unsigned nr_ticks;
 162
 163                /* Get number of ticks performed before irq, and ack it */
 164                nr_ticks = PIT_PICNT(pit_read(data->base, AT91_PIT_PIVR));
 165                do {
 166                        data->cnt += data->cycle;
 167                        data->clkevt.event_handler(&data->clkevt);
 168                        nr_ticks--;
 169                } while (nr_ticks);
 170
 171                return IRQ_HANDLED;
 172        }
 173
 174        return IRQ_NONE;
 175}
 176
 177/*
 178 * Set up both clocksource and clockevent support.
 179 */
 180static void __init at91sam926x_pit_common_init(struct pit_data *data)
 181{
 182        unsigned long   pit_rate;
 183        unsigned        bits;
 184        int             ret;
 185
 186        /*
 187         * Use our actual MCK to figure out how many MCK/16 ticks per
 188         * 1/HZ period (instead of a compile-time constant LATCH).
 189         */
 190        pit_rate = clk_get_rate(data->mck) / 16;
 191        data->cycle = DIV_ROUND_CLOSEST(pit_rate, HZ);
 192        WARN_ON(((data->cycle - 1) & ~AT91_PIT_PIV) != 0);
 193
 194        /* Initialize and enable the timer */
 195        at91sam926x_pit_reset(data);
 196
 197        /*
 198         * Register clocksource.  The high order bits of PIV are unused,
 199         * so this isn't a 32-bit counter unless we get clockevent irqs.
 200         */
 201        bits = 12 /* PICNT */ + ilog2(data->cycle) /* PIV */;
 202        data->clksrc.mask = CLOCKSOURCE_MASK(bits);
 203        data->clksrc.name = "pit";
 204        data->clksrc.rating = 175;
 205        data->clksrc.read = read_pit_clk;
 206        data->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
 207        clocksource_register_hz(&data->clksrc, pit_rate);
 208
 209        /* Set up irq handler */
 210        ret = request_irq(data->irq, at91sam926x_pit_interrupt,
 211                          IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
 212                          "at91_tick", data);
 213        if (ret)
 214                panic(pr_fmt("Unable to setup IRQ\n"));
 215
 216        /* Set up and register clockevents */
 217        data->clkevt.name = "pit";
 218        data->clkevt.features = CLOCK_EVT_FEAT_PERIODIC;
 219        data->clkevt.shift = 32;
 220        data->clkevt.mult = div_sc(pit_rate, NSEC_PER_SEC, data->clkevt.shift);
 221        data->clkevt.rating = 100;
 222        data->clkevt.cpumask = cpumask_of(0);
 223
 224        data->clkevt.set_state_shutdown = pit_clkevt_shutdown;
 225        data->clkevt.set_state_periodic = pit_clkevt_set_periodic;
 226        data->clkevt.resume = at91sam926x_pit_resume;
 227        data->clkevt.suspend = at91sam926x_pit_suspend;
 228        clockevents_register_device(&data->clkevt);
 229}
 230
 231static void __init at91sam926x_pit_dt_init(struct device_node *node)
 232{
 233        struct pit_data *data;
 234
 235        data = kzalloc(sizeof(*data), GFP_KERNEL);
 236        if (!data)
 237                panic(pr_fmt("Unable to allocate memory\n"));
 238
 239        data->base = of_iomap(node, 0);
 240        if (!data->base)
 241                panic(pr_fmt("Could not map PIT address\n"));
 242
 243        data->mck = of_clk_get(node, 0);
 244        if (IS_ERR(data->mck))
 245                /* Fallback on clkdev for !CCF-based boards */
 246                data->mck = clk_get(NULL, "mck");
 247
 248        if (IS_ERR(data->mck))
 249                panic(pr_fmt("Unable to get mck clk\n"));
 250
 251        /* Get the interrupts property */
 252        data->irq = irq_of_parse_and_map(node, 0);
 253        if (!data->irq)
 254                panic(pr_fmt("Unable to get IRQ from DT\n"));
 255
 256        at91sam926x_pit_common_init(data);
 257}
 258CLOCKSOURCE_OF_DECLARE(at91sam926x_pit, "atmel,at91sam9260-pit",
 259                       at91sam926x_pit_dt_init);
 260