arch/arm/plat-omap/counter_32k.c

   1 /*
   2  * OMAP 32ksynctimer/counter_32k-related code
   3  *
   4  * Copyright (C) 2009 Texas Instruments
   5  * Copyright (C) 2010 Nokia Corporation
   6  * Tony Lindgren <tony@atomide.com>
   7  * Added OMAP4 support - Santosh Shilimkar <santosh.shilimkar@ti.com>
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  *
  13  * NOTE: This timer is not the same timer as the old OMAP1 MPU timer.
  14  */
  15 #include <linux/kernel.h>
  16 #include <linux/init.h>
  17 #include <linux/clk.h>
  18 #include <linux/err.h>
  19 #include <linux/io.h>
  20 #include <linux/clocksource.h>
  21 #include <linux/sched_clock.h>
  22
  23 #include <asm/mach/time.h>
  24
  25 #include <plat/counter-32k.h>
  26
  27 /* OMAP2_32KSYNCNT_CR_OFF: offset of 32ksync counter register */
  28 #define OMAP2_32KSYNCNT_REV_OFF         0x0
  29 #define OMAP2_32KSYNCNT_REV_SCHEME      (0x3 << 30)
  30 #define OMAP2_32KSYNCNT_CR_OFF_LOW      0x10
  31 #define OMAP2_32KSYNCNT_CR_OFF_HIGH     0x30
  32
  33 /*
  34  * 32KHz clocksource ... always available, on pretty most chips except
  35  * OMAP 730 and 1510.  Other timers could be used as clocksources, with
  36  * higher resolution in free-running counter modes (e.g. 12 MHz xtal),
  37  * but systems won't necessarily want to spend resources that way.
  38  */
  39 static void __iomem *sync32k_cnt_reg;
  40
  41 static u64 notrace omap_32k_read_sched_clock(void)
  42 {
  43         return sync32k_cnt_reg ? readl_relaxed(sync32k_cnt_reg) : 0;
  44 }
  45
  46 /**
  47  * omap_read_persistent_clock -  Return time from a persistent clock.
  48  *
  49  * Reads the time from a source which isn't disabled during PM, the
  50  * 32k sync timer.  Convert the cycles elapsed since last read into
  51  * nsecs and adds to a monotonically increasing timespec.
  52  */
  53 static struct timespec persistent_ts;
  54 static cycles_t cycles;
  55 static unsigned int persistent_mult, persistent_shift;
  56 static DEFINE_SPINLOCK(read_persistent_clock_lock);
  57
  58 static void omap_read_persistent_clock(struct timespec *ts)
  59 {
  60         unsigned long long nsecs;
  61         cycles_t last_cycles;
  62         unsigned long flags;
  63
  64         spin_lock_irqsave(&read_persistent_clock_lock, flags);
  65
  66         last_cycles = cycles;
  67         cycles = sync32k_cnt_reg ? readl_relaxed(sync32k_cnt_reg) : 0;
  68
  69         nsecs = clocksource_cyc2ns(cycles - last_cycles,
  70                                         persistent_mult, persistent_shift);
  71
  72         timespec_add_ns(&persistent_ts, nsecs);
  73
  74         *ts = persistent_ts;
  75
  76         spin_unlock_irqrestore(&read_persistent_clock_lock, flags);
  77 }
  78
  79 /**
  80  * omap_init_clocksource_32k - setup and register counter 32k as a
  81  * kernel clocksource
  82  * @pbase: base addr of counter_32k module
  83  * @size: size of counter_32k to map
  84  *
  85  * Returns 0 upon success or negative error code upon failure.
  86  *
  87  */
  88 int __init omap_init_clocksource_32k(void __iomem *vbase)
  89 {
  90         int ret;
  91
  92         /*
  93          * 32k sync Counter IP register offsets vary between the
  94          * highlander version and the legacy ones.
  95          * The 'SCHEME' bits(30-31) of the revision register is used
  96          * to identify the version.
  97          */
  98         if (readl_relaxed(vbase + OMAP2_32KSYNCNT_REV_OFF) &
  99                                                 OMAP2_32KSYNCNT_REV_SCHEME)
 100                 sync32k_cnt_reg = vbase + OMAP2_32KSYNCNT_CR_OFF_HIGH;
 101         else
 102                 sync32k_cnt_reg = vbase + OMAP2_32KSYNCNT_CR_OFF_LOW;
 103
 104         /*
 105          * 120000 rough estimate from the calculations in
 106          * __clocksource_updatefreq_scale.
 107          */
 108         clocks_calc_mult_shift(&persistent_mult, &persistent_shift,
 109                         32768, NSEC_PER_SEC, 120000);
 110
 111         ret = clocksource_mmio_init(sync32k_cnt_reg, "32k_counter", 32768,
 112                                 250, 32, clocksource_mmio_readl_up);
 113         if (ret) {
 114                 pr_err("32k_counter: can't register clocksource\n");
 115                 return ret;
 116         }
 117
 118         sched_clock_register(omap_32k_read_sched_clock, 32, 32768);
 119         register_persistent_clock(NULL, omap_read_persistent_clock);
 120         pr_info("OMAP clocksource: 32k_counter at 32768 Hz\n");
 121
 122         return 0;
 123 }