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/clockchips.h>
  16 #include <linux/clksrc-dbx500-prcmu.h>
  17 #include <linux/sched_clock.h>
  18
  19 #define RATE_32K                32768
  20
  21 #define TIMER_MODE_CONTINOUS    0x1
  22 #define TIMER_DOWNCOUNT_VAL     0xffffffff
  23
  24 #define PRCMU_TIMER_REF         0
  25 #define PRCMU_TIMER_DOWNCOUNT   0x4
  26 #define PRCMU_TIMER_MODE        0x8
  27
  28 #define SCHED_CLOCK_MIN_WRAP 131072 /* 2^32 / 32768 */
  29
  30 static void __iomem *clksrc_dbx500_timer_base;
  31
  32 static cycle_t notrace clksrc_dbx500_prcmu_read(struct clocksource *cs)
  33 {
  34         void __iomem *base = clksrc_dbx500_timer_base;
  35         u32 count, count2;
  36
  37         do {
  38                 count = readl_relaxed(base + PRCMU_TIMER_DOWNCOUNT);
  39                 count2 = readl_relaxed(base + PRCMU_TIMER_DOWNCOUNT);
  40         } while (count2 != count);
  41
  42         /* Negate because the timer is a decrementing counter */
  43         return ~count;
  44 }
  45
  46 static struct clocksource clocksource_dbx500_prcmu = {
  47         .name           = "dbx500-prcmu-timer",
  48         .rating         = 300,
  49         .read           = clksrc_dbx500_prcmu_read,
  50         .mask           = CLOCKSOURCE_MASK(32),
  51         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  52 };
  53
  54 #ifdef CONFIG_CLKSRC_DBX500_PRCMU_SCHED_CLOCK
  55
  56 static u64 notrace dbx500_prcmu_sched_clock_read(void)
  57 {
  58         if (unlikely(!clksrc_dbx500_timer_base))
  59                 return 0;
  60
  61         return clksrc_dbx500_prcmu_read(&clocksource_dbx500_prcmu);
  62 }
  63
  64 #endif
  65
  66 void __init clksrc_dbx500_prcmu_init(void __iomem *base)
  67 {
  68         clksrc_dbx500_timer_base = base;
  69
  70         /*
  71          * The A9 sub system expects the timer to be configured as
  72          * a continous looping timer.
  73          * The PRCMU should configure it but if it for some reason
  74          * don't we do it here.
  75          */
  76         if (readl(clksrc_dbx500_timer_base + PRCMU_TIMER_MODE) !=
  77             TIMER_MODE_CONTINOUS) {
  78                 writel(TIMER_MODE_CONTINOUS,
  79                        clksrc_dbx500_timer_base + PRCMU_TIMER_MODE);
  80                 writel(TIMER_DOWNCOUNT_VAL,
  81                        clksrc_dbx500_timer_base + PRCMU_TIMER_REF);
  82         }
  83 #ifdef CONFIG_CLKSRC_DBX500_PRCMU_SCHED_CLOCK
  84         sched_clock_register(dbx500_prcmu_sched_clock_read, 32, RATE_32K);
  85 #endif
  86         clocksource_register_hz(&clocksource_dbx500_prcmu, RATE_32K);
  87 }