drivers/clocksource/clksrc-dbx500-prcmu.c

   1 /*
   2  * Copyright (C) ST-Ericsson SA 2011
   3  *
   4  * License Terms: GNU General Public License v2
   5  * Author: Mattias Wallin <mattias.wallin@stericsson.com> for ST-Ericsson
   6  * Author: Sundar Iyer for ST-Ericsson
   7  * sched_clock implementation is based on:
   8  * plat-nomadik/timer.c Linus Walleij <linus.walleij@stericsson.com>
   9  *
  10  * DBx500-PRCMU Timer
  11  * The PRCMU has 5 timers which are available in a always-on
  12  * power domain.  We use the Timer 4 for our always-on clock
  13  * source on DB8500.
  14  */
  15 #include <linux/of.h>
  16 #include <linux/of_address.h>
  17 #include <linux/clockchips.h>
  18 #include <linux/sched_clock.h>
  19
  20 #define RATE_32K                32768
  21
  22 #define TIMER_MODE_CONTINOUS    0x1
  23 #define TIMER_DOWNCOUNT_VAL     0xffffffff
  24
  25 #define PRCMU_TIMER_REF         0
  26 #define PRCMU_TIMER_DOWNCOUNT   0x4
  27 #define PRCMU_TIMER_MODE        0x8
  28
  29 #define SCHED_CLOCK_MIN_WRAP 131072 /* 2^32 / 32768 */
  30
  31 static void __iomem *clksrc_dbx500_timer_base;
  32
  33 static u64 notrace clksrc_dbx500_prcmu_read(struct clocksource *cs)
  34 {
  35         void __iomem *base = clksrc_dbx500_timer_base;
  36         u32 count, count2;
  37
  38         do {
  39                 count = readl_relaxed(base + PRCMU_TIMER_DOWNCOUNT);
  40                 count2 = readl_relaxed(base + PRCMU_TIMER_DOWNCOUNT);
  41         } while (count2 != count);
  42
  43         /* Negate because the timer is a decrementing counter */
  44         return ~count;
  45 }
  46
  47 static struct clocksource clocksource_dbx500_prcmu = {
  48         .name           = "dbx500-prcmu-timer",
  49         .rating         = 300,
  50         .read           = clksrc_dbx500_prcmu_read,
  51         .mask           = CLOCKSOURCE_MASK(32),
  52         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  53 };
  54
  55 #ifdef CONFIG_CLKSRC_DBX500_PRCMU_SCHED_CLOCK
  56
  57 static u64 notrace dbx500_prcmu_sched_clock_read(void)
  58 {
  59         if (unlikely(!clksrc_dbx500_timer_base))
  60                 return 0;
  61
  62         return clksrc_dbx500_prcmu_read(&clocksource_dbx500_prcmu);
  63 }
  64
  65 #endif
  66
  67 static int __init clksrc_dbx500_prcmu_init(struct device_node *node)
  68 {
  69         clksrc_dbx500_timer_base = of_iomap(node, 0);
  70
  71         /*
  72          * The A9 sub system expects the timer to be configured as
  73          * a continous looping timer.
  74          * The PRCMU should configure it but if it for some reason
  75          * don't we do it here.
  76          */
  77         if (readl(clksrc_dbx500_timer_base + PRCMU_TIMER_MODE) !=
  78             TIMER_MODE_CONTINOUS) {
  79                 writel(TIMER_MODE_CONTINOUS,
  80                        clksrc_dbx500_timer_base + PRCMU_TIMER_MODE);
  81                 writel(TIMER_DOWNCOUNT_VAL,
  82                        clksrc_dbx500_timer_base + PRCMU_TIMER_REF);
  83         }
  84 #ifdef CONFIG_CLKSRC_DBX500_PRCMU_SCHED_CLOCK
  85         sched_clock_register(dbx500_prcmu_sched_clock_read, 32, RATE_32K);
  86 #endif
  87         return clocksource_register_hz(&clocksource_dbx500_prcmu, RATE_32K);
  88 }
  89 CLOCKSOURCE_OF_DECLARE(dbx500_prcmu, "stericsson,db8500-prcmu-timer-4",
  90                        clksrc_dbx500_prcmu_init);