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
  41 struct 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
  52 static inline struct pit_data *clksrc_to_pit_data(struct clocksource *clksrc)
  53 {
  54         return container_of(clksrc, struct pit_data, clksrc);
  55 }
  56
  57 static 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
  62 static inline unsigned int pit_read(void __iomem *base, unsigned int reg_offset)
  63 {
  64         return readl_relaxed(base + reg_offset);
  65 }
  66
  67 static 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  */
  76 static 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
  93 static 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  */
 105 static 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
 116 static 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
 124 static 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
 138 static 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  */
 148 static 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  */
 180 static 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
 231 static 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 }
 258 CLOCKSOURCE_OF_DECLARE(at91sam926x_pit, "atmel,at91sam9260-pit",
 259                        at91sam926x_pit_dt_init);