drivers/clocksource/timer-atmel-st.c

   1 /*
   2  * linux/arch/arm/mach-at91/at91rm9200_time.c
   3  *
   4  *  Copyright (C) 2003 SAN People
   5  *  Copyright (C) 2003 ATMEL
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20  */
  21
  22 #include <linux/kernel.h>
  23 #include <linux/interrupt.h>
  24 #include <linux/irq.h>
  25 #include <linux/clk.h>
  26 #include <linux/clockchips.h>
  27 #include <linux/export.h>
  28 #include <linux/mfd/syscon.h>
  29 #include <linux/mfd/syscon/atmel-st.h>
  30 #include <linux/of_irq.h>
  31 #include <linux/regmap.h>
  32
  33 static unsigned long last_crtr;
  34 static u32 irqmask;
  35 static struct clock_event_device clkevt;
  36 static struct regmap *regmap_st;
  37 static int timer_latch;
  38
  39 /*
  40  * The ST_CRTR is updated asynchronously to the master clock ... but
  41  * the updates as seen by the CPU don't seem to be strictly monotonic.
  42  * Waiting until we read the same value twice avoids glitching.
  43  */
  44 static inline unsigned long read_CRTR(void)
  45 {
  46         unsigned int x1, x2;
  47
  48         regmap_read(regmap_st, AT91_ST_CRTR, &x1);
  49         do {
  50                 regmap_read(regmap_st, AT91_ST_CRTR, &x2);
  51                 if (x1 == x2)
  52                         break;
  53                 x1 = x2;
  54         } while (1);
  55         return x1;
  56 }
  57
  58 /*
  59  * IRQ handler for the timer.
  60  */
  61 static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
  62 {
  63         u32 sr;
  64
  65         regmap_read(regmap_st, AT91_ST_SR, &sr);
  66         sr &= irqmask;
  67
  68         /*
  69          * irqs should be disabled here, but as the irq is shared they are only
  70          * guaranteed to be off if the timer irq is registered first.
  71          */
  72         WARN_ON_ONCE(!irqs_disabled());
  73
  74         /* simulate "oneshot" timer with alarm */
  75         if (sr & AT91_ST_ALMS) {
  76                 clkevt.event_handler(&clkevt);
  77                 return IRQ_HANDLED;
  78         }
  79
  80         /* periodic mode should handle delayed ticks */
  81         if (sr & AT91_ST_PITS) {
  82                 u32     crtr = read_CRTR();
  83
  84                 while (((crtr - last_crtr) & AT91_ST_CRTV) >= timer_latch) {
  85                         last_crtr += timer_latch;
  86                         clkevt.event_handler(&clkevt);
  87                 }
  88                 return IRQ_HANDLED;
  89         }
  90
  91         /* this irq is shared ... */
  92         return IRQ_NONE;
  93 }
  94
  95 static u64 read_clk32k(struct clocksource *cs)
  96 {
  97         return read_CRTR();
  98 }
  99
 100 static struct clocksource clk32k = {
 101         .name           = "32k_counter",
 102         .rating         = 150,
 103         .read           = read_clk32k,
 104         .mask           = CLOCKSOURCE_MASK(20),
 105         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
 106 };
 107
 108 static void clkdev32k_disable_and_flush_irq(void)
 109 {
 110         unsigned int val;
 111
 112         /* Disable and flush pending timer interrupts */
 113         regmap_write(regmap_st, AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
 114         regmap_read(regmap_st, AT91_ST_SR, &val);
 115         last_crtr = read_CRTR();
 116 }
 117
 118 static int clkevt32k_shutdown(struct clock_event_device *evt)
 119 {
 120         clkdev32k_disable_and_flush_irq();
 121         irqmask = 0;
 122         regmap_write(regmap_st, AT91_ST_IER, irqmask);
 123         return 0;
 124 }
 125
 126 static int clkevt32k_set_oneshot(struct clock_event_device *dev)
 127 {
 128         clkdev32k_disable_and_flush_irq();
 129
 130         /*
 131          * ALM for oneshot irqs, set by next_event()
 132          * before 32 seconds have passed.
 133          */
 134         irqmask = AT91_ST_ALMS;
 135         regmap_write(regmap_st, AT91_ST_RTAR, last_crtr);
 136         regmap_write(regmap_st, AT91_ST_IER, irqmask);
 137         return 0;
 138 }
 139
 140 static int clkevt32k_set_periodic(struct clock_event_device *dev)
 141 {
 142         clkdev32k_disable_and_flush_irq();
 143
 144         /* PIT for periodic irqs; fixed rate of 1/HZ */
 145         irqmask = AT91_ST_PITS;
 146         regmap_write(regmap_st, AT91_ST_PIMR, timer_latch);
 147         regmap_write(regmap_st, AT91_ST_IER, irqmask);
 148         return 0;
 149 }
 150
 151 static int
 152 clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
 153 {
 154         u32             alm;
 155         int             status = 0;
 156         unsigned int    val;
 157
 158         BUG_ON(delta < 2);
 159
 160         /* The alarm IRQ uses absolute time (now+delta), not the relative
 161          * time (delta) in our calling convention.  Like all clockevents
 162          * using such "match" hardware, we have a race to defend against.
 163          *
 164          * Our defense here is to have set up the clockevent device so the
 165          * delta is at least two.  That way we never end up writing RTAR
 166          * with the value then held in CRTR ... which would mean the match
 167          * wouldn't trigger until 32 seconds later, after CRTR wraps.
 168          */
 169         alm = read_CRTR();
 170
 171         /* Cancel any pending alarm; flush any pending IRQ */
 172         regmap_write(regmap_st, AT91_ST_RTAR, alm);
 173         regmap_read(regmap_st, AT91_ST_SR, &val);
 174
 175         /* Schedule alarm by writing RTAR. */
 176         alm += delta;
 177         regmap_write(regmap_st, AT91_ST_RTAR, alm);
 178
 179         return status;
 180 }
 181
 182 static struct clock_event_device clkevt = {
 183         .name                   = "at91_tick",
 184         .features               = CLOCK_EVT_FEAT_PERIODIC |
 185                                   CLOCK_EVT_FEAT_ONESHOT,
 186         .rating                 = 150,
 187         .set_next_event         = clkevt32k_next_event,
 188         .set_state_shutdown     = clkevt32k_shutdown,
 189         .set_state_periodic     = clkevt32k_set_periodic,
 190         .set_state_oneshot      = clkevt32k_set_oneshot,
 191         .tick_resume            = clkevt32k_shutdown,
 192 };
 193
 194 /*
 195  * ST (system timer) module supports both clockevents and clocksource.
 196  */
 197 static int __init atmel_st_timer_init(struct device_node *node)
 198 {
 199         struct clk *sclk;
 200         unsigned int sclk_rate, val;
 201         int irq, ret;
 202
 203         regmap_st = syscon_node_to_regmap(node);
 204         if (IS_ERR(regmap_st)) {
 205                 pr_err("Unable to get regmap\n");
 206                 return PTR_ERR(regmap_st);
 207         }
 208
 209         /* Disable all timer interrupts, and clear any pending ones */
 210         regmap_write(regmap_st, AT91_ST_IDR,
 211                 AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
 212         regmap_read(regmap_st, AT91_ST_SR, &val);
 213
 214         /* Get the interrupts property */
 215         irq  = irq_of_parse_and_map(node, 0);
 216         if (!irq) {
 217                 pr_err("Unable to get IRQ from DT\n");
 218                 return -EINVAL;
 219         }
 220
 221         /* Make IRQs happen for the system timer */
 222         ret = request_irq(irq, at91rm9200_timer_interrupt,
 223                           IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
 224                           "at91_tick", regmap_st);
 225         if (ret) {
 226                 pr_err("Unable to setup IRQ\n");
 227                 return ret;
 228         }
 229
 230         sclk = of_clk_get(node, 0);
 231         if (IS_ERR(sclk)) {
 232                 pr_err("Unable to get slow clock\n");
 233                 return PTR_ERR(sclk);
 234         }
 235
 236         ret = clk_prepare_enable(sclk);
 237         if (ret) {
 238                 pr_err("Could not enable slow clock\n");
 239                 return ret;
 240         }
 241
 242         sclk_rate = clk_get_rate(sclk);
 243         if (!sclk_rate) {
 244                 pr_err("Invalid slow clock rate\n");
 245                 return -EINVAL;
 246         }
 247         timer_latch = (sclk_rate + HZ / 2) / HZ;
 248
 249         /* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
 250          * directly for the clocksource and all clockevents, after adjusting
 251          * its prescaler from the 1 Hz default.
 252          */
 253         regmap_write(regmap_st, AT91_ST_RTMR, 1);
 254
 255         /* Setup timer clockevent, with minimum of two ticks (important!!) */
 256         clkevt.cpumask = cpumask_of(0);
 257         clockevents_config_and_register(&clkevt, sclk_rate,
 258                                         2, AT91_ST_ALMV);
 259
 260         /* register clocksource */
 261         return clocksource_register_hz(&clk32k, sclk_rate);
 262 }
 263 TIMER_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st",
 264                        atmel_st_timer_init);