drivers/clocksource/timer-atmel-st.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * linux/arch/arm/mach-at91/at91rm9200_time.c
   4  *
   5  *  Copyright (C) 2003 SAN People
   6  *  Copyright (C) 2003 ATMEL
   7  */
   8
   9 #include <linux/kernel.h>
  10 #include <linux/interrupt.h>
  11 #include <linux/irq.h>
  12 #include <linux/clk.h>
  13 #include <linux/clockchips.h>
  14 #include <linux/export.h>
  15 #include <linux/mfd/syscon.h>
  16 #include <linux/mfd/syscon/atmel-st.h>
  17 #include <linux/of_irq.h>
  18 #include <linux/regmap.h>
  19
  20 static unsigned long last_crtr;
  21 static u32 irqmask;
  22 static struct clock_event_device clkevt;
  23 static struct regmap *regmap_st;
  24 static int timer_latch;
  25
  26 /*
  27  * The ST_CRTR is updated asynchronously to the master clock ... but
  28  * the updates as seen by the CPU don't seem to be strictly monotonic.
  29  * Waiting until we read the same value twice avoids glitching.
  30  */
  31 static inline unsigned long read_CRTR(void)
  32 {
  33         unsigned int x1, x2;
  34
  35         regmap_read(regmap_st, AT91_ST_CRTR, &x1);
  36         do {
  37                 regmap_read(regmap_st, AT91_ST_CRTR, &x2);
  38                 if (x1 == x2)
  39                         break;
  40                 x1 = x2;
  41         } while (1);
  42         return x1;
  43 }
  44
  45 /*
  46  * IRQ handler for the timer.
  47  */
  48 static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
  49 {
  50         u32 sr;
  51
  52         regmap_read(regmap_st, AT91_ST_SR, &sr);
  53         sr &= irqmask;
  54
  55         /*
  56          * irqs should be disabled here, but as the irq is shared they are only
  57          * guaranteed to be off if the timer irq is registered first.
  58          */
  59         WARN_ON_ONCE(!irqs_disabled());
  60
  61         /* simulate "oneshot" timer with alarm */
  62         if (sr & AT91_ST_ALMS) {
  63                 clkevt.event_handler(&clkevt);
  64                 return IRQ_HANDLED;
  65         }
  66
  67         /* periodic mode should handle delayed ticks */
  68         if (sr & AT91_ST_PITS) {
  69                 u32     crtr = read_CRTR();
  70
  71                 while (((crtr - last_crtr) & AT91_ST_CRTV) >= timer_latch) {
  72                         last_crtr += timer_latch;
  73                         clkevt.event_handler(&clkevt);
  74                 }
  75                 return IRQ_HANDLED;
  76         }
  77
  78         /* this irq is shared ... */
  79         return IRQ_NONE;
  80 }
  81
  82 static u64 read_clk32k(struct clocksource *cs)
  83 {
  84         return read_CRTR();
  85 }
  86
  87 static struct clocksource clk32k = {
  88         .name           = "32k_counter",
  89         .rating         = 150,
  90         .read           = read_clk32k,
  91         .mask           = CLOCKSOURCE_MASK(20),
  92         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  93 };
  94
  95 static void clkdev32k_disable_and_flush_irq(void)
  96 {
  97         unsigned int val;
  98
  99         /* Disable and flush pending timer interrupts */
 100         regmap_write(regmap_st, AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
 101         regmap_read(regmap_st, AT91_ST_SR, &val);
 102         last_crtr = read_CRTR();
 103 }
 104
 105 static int clkevt32k_shutdown(struct clock_event_device *evt)
 106 {
 107         clkdev32k_disable_and_flush_irq();
 108         irqmask = 0;
 109         regmap_write(regmap_st, AT91_ST_IER, irqmask);
 110         return 0;
 111 }
 112
 113 static int clkevt32k_set_oneshot(struct clock_event_device *dev)
 114 {
 115         clkdev32k_disable_and_flush_irq();
 116
 117         /*
 118          * ALM for oneshot irqs, set by next_event()
 119          * before 32 seconds have passed.
 120          */
 121         irqmask = AT91_ST_ALMS;
 122         regmap_write(regmap_st, AT91_ST_RTAR, last_crtr);
 123         regmap_write(regmap_st, AT91_ST_IER, irqmask);
 124         return 0;
 125 }
 126
 127 static int clkevt32k_set_periodic(struct clock_event_device *dev)
 128 {
 129         clkdev32k_disable_and_flush_irq();
 130
 131         /* PIT for periodic irqs; fixed rate of 1/HZ */
 132         irqmask = AT91_ST_PITS;
 133         regmap_write(regmap_st, AT91_ST_PIMR, timer_latch);
 134         regmap_write(regmap_st, AT91_ST_IER, irqmask);
 135         return 0;
 136 }
 137
 138 static int
 139 clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
 140 {
 141         u32             alm;
 142         unsigned int    val;
 143
 144         BUG_ON(delta < 2);
 145
 146         /* The alarm IRQ uses absolute time (now+delta), not the relative
 147          * time (delta) in our calling convention.  Like all clockevents
 148          * using such "match" hardware, we have a race to defend against.
 149          *
 150          * Our defense here is to have set up the clockevent device so the
 151          * delta is at least two.  That way we never end up writing RTAR
 152          * with the value then held in CRTR ... which would mean the match
 153          * wouldn't trigger until 32 seconds later, after CRTR wraps.
 154          */
 155         alm = read_CRTR();
 156
 157         /* Cancel any pending alarm; flush any pending IRQ */
 158         regmap_write(regmap_st, AT91_ST_RTAR, alm);
 159         regmap_read(regmap_st, AT91_ST_SR, &val);
 160
 161         /* Schedule alarm by writing RTAR. */
 162         alm += delta;
 163         regmap_write(regmap_st, AT91_ST_RTAR, alm);
 164
 165         return 0;
 166 }
 167
 168 static struct clock_event_device clkevt = {
 169         .name                   = "at91_tick",
 170         .features               = CLOCK_EVT_FEAT_PERIODIC |
 171                                   CLOCK_EVT_FEAT_ONESHOT,
 172         .rating                 = 150,
 173         .set_next_event         = clkevt32k_next_event,
 174         .set_state_shutdown     = clkevt32k_shutdown,
 175         .set_state_periodic     = clkevt32k_set_periodic,
 176         .set_state_oneshot      = clkevt32k_set_oneshot,
 177         .tick_resume            = clkevt32k_shutdown,
 178 };
 179
 180 /*
 181  * ST (system timer) module supports both clockevents and clocksource.
 182  */
 183 static int __init atmel_st_timer_init(struct device_node *node)
 184 {
 185         struct clk *sclk;
 186         unsigned int sclk_rate, val;
 187         int irq, ret;
 188
 189         regmap_st = syscon_node_to_regmap(node);
 190         if (IS_ERR(regmap_st)) {
 191                 pr_err("Unable to get regmap\n");
 192                 return PTR_ERR(regmap_st);
 193         }
 194
 195         /* Disable all timer interrupts, and clear any pending ones */
 196         regmap_write(regmap_st, AT91_ST_IDR,
 197                 AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
 198         regmap_read(regmap_st, AT91_ST_SR, &val);
 199
 200         /* Get the interrupts property */
 201         irq  = irq_of_parse_and_map(node, 0);
 202         if (!irq) {
 203                 pr_err("Unable to get IRQ from DT\n");
 204                 return -EINVAL;
 205         }
 206
 207         /* Make IRQs happen for the system timer */
 208         ret = request_irq(irq, at91rm9200_timer_interrupt,
 209                           IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
 210                           "at91_tick", regmap_st);
 211         if (ret) {
 212                 pr_err("Unable to setup IRQ\n");
 213                 return ret;
 214         }
 215
 216         sclk = of_clk_get(node, 0);
 217         if (IS_ERR(sclk)) {
 218                 pr_err("Unable to get slow clock\n");
 219                 return PTR_ERR(sclk);
 220         }
 221
 222         ret = clk_prepare_enable(sclk);
 223         if (ret) {
 224                 pr_err("Could not enable slow clock\n");
 225                 return ret;
 226         }
 227
 228         sclk_rate = clk_get_rate(sclk);
 229         if (!sclk_rate) {
 230                 pr_err("Invalid slow clock rate\n");
 231                 return -EINVAL;
 232         }
 233         timer_latch = (sclk_rate + HZ / 2) / HZ;
 234
 235         /* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
 236          * directly for the clocksource and all clockevents, after adjusting
 237          * its prescaler from the 1 Hz default.
 238          */
 239         regmap_write(regmap_st, AT91_ST_RTMR, 1);
 240
 241         /* Setup timer clockevent, with minimum of two ticks (important!!) */
 242         clkevt.cpumask = cpumask_of(0);
 243         clockevents_config_and_register(&clkevt, sclk_rate,
 244                                         2, AT91_ST_ALMV);
 245
 246         /* register clocksource */
 247         return clocksource_register_hz(&clk32k, sclk_rate);
 248 }
 249 TIMER_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st",
 250                        atmel_st_timer_init);