root/drivers/clocksource/timer-atmel-st.c

DEFINITIONS

1. read_CRTR
2. at91rm9200_timer_interrupt
3. read_clk32k
4. clkdev32k_disable_and_flush_irq
5. clkevt32k_shutdown
6. clkevt32k_set_oneshot
7. clkevt32k_set_periodic
8. clkevt32k_next_event
9. atmel_st_timer_init

   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         int             status = 0;
 143         unsigned int    val;
 144 
 145         BUG_ON(delta < 2);
 146 
 147         /* The alarm IRQ uses absolute time (now+delta), not the relative
 148          * time (delta) in our calling convention.  Like all clockevents
 149          * using such "match" hardware, we have a race to defend against.
 150          *
 151          * Our defense here is to have set up the clockevent device so the
 152          * delta is at least two.  That way we never end up writing RTAR
 153          * with the value then held in CRTR ... which would mean the match
 154          * wouldn't trigger until 32 seconds later, after CRTR wraps.
 155          */
 156         alm = read_CRTR();
 157 
 158         /* Cancel any pending alarm; flush any pending IRQ */
 159         regmap_write(regmap_st, AT91_ST_RTAR, alm);
 160         regmap_read(regmap_st, AT91_ST_SR, &val);
 161 
 162         /* Schedule alarm by writing RTAR. */
 163         alm += delta;
 164         regmap_write(regmap_st, AT91_ST_RTAR, alm);
 165 
 166         return status;
 167 }
 168 
 169 static struct clock_event_device clkevt = {
 170         .name                   = "at91_tick",
 171         .features               = CLOCK_EVT_FEAT_PERIODIC |
 172                                   CLOCK_EVT_FEAT_ONESHOT,
 173         .rating                 = 150,
 174         .set_next_event         = clkevt32k_next_event,
 175         .set_state_shutdown     = clkevt32k_shutdown,
 176         .set_state_periodic     = clkevt32k_set_periodic,
 177         .set_state_oneshot      = clkevt32k_set_oneshot,
 178         .tick_resume            = clkevt32k_shutdown,
 179 };
 180 
 181 /*
 182  * ST (system timer) module supports both clockevents and clocksource.
 183  */
 184 static int __init atmel_st_timer_init(struct device_node *node)
 185 {
 186         struct clk *sclk;
 187         unsigned int sclk_rate, val;
 188         int irq, ret;
 189 
 190         regmap_st = syscon_node_to_regmap(node);
 191         if (IS_ERR(regmap_st)) {
 192                 pr_err("Unable to get regmap\n");
 193                 return PTR_ERR(regmap_st);
 194         }
 195 
 196         /* Disable all timer interrupts, and clear any pending ones */
 197         regmap_write(regmap_st, AT91_ST_IDR,
 198                 AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
 199         regmap_read(regmap_st, AT91_ST_SR, &val);
 200 
 201         /* Get the interrupts property */
 202         irq  = irq_of_parse_and_map(node, 0);
 203         if (!irq) {
 204                 pr_err("Unable to get IRQ from DT\n");
 205                 return -EINVAL;
 206         }
 207 
 208         /* Make IRQs happen for the system timer */
 209         ret = request_irq(irq, at91rm9200_timer_interrupt,
 210                           IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
 211                           "at91_tick", regmap_st);
 212         if (ret) {
 213                 pr_err("Unable to setup IRQ\n");
 214                 return ret;
 215         }
 216 
 217         sclk = of_clk_get(node, 0);
 218         if (IS_ERR(sclk)) {
 219                 pr_err("Unable to get slow clock\n");
 220                 return PTR_ERR(sclk);
 221         }
 222 
 223         ret = clk_prepare_enable(sclk);
 224         if (ret) {
 225                 pr_err("Could not enable slow clock\n");
 226                 return ret;
 227         }
 228 
 229         sclk_rate = clk_get_rate(sclk);
 230         if (!sclk_rate) {
 231                 pr_err("Invalid slow clock rate\n");
 232                 return -EINVAL;
 233         }
 234         timer_latch = (sclk_rate + HZ / 2) / HZ;
 235 
 236         /* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
 237          * directly for the clocksource and all clockevents, after adjusting
 238          * its prescaler from the 1 Hz default.
 239          */
 240         regmap_write(regmap_st, AT91_ST_RTMR, 1);
 241 
 242         /* Setup timer clockevent, with minimum of two ticks (important!!) */
 243         clkevt.cpumask = cpumask_of(0);
 244         clockevents_config_and_register(&clkevt, sclk_rate,
 245                                         2, AT91_ST_ALMV);
 246 
 247         /* register clocksource */
 248         return clocksource_register_hz(&clk32k, sclk_rate);
 249 }
 250 TIMER_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st",
 251                        atmel_st_timer_init);