arch/mips/kernel/csrc-ioasic.c

   1 /*
   2  *  DEC I/O ASIC's counter clocksource
   3  *
   4  *  Copyright (C) 2008  Yoichi Yuasa <yuasa@linux-mips.org>
   5  *
   6  *  This program is free software; you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation; either version 2 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  This program is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  */
  16 #include <linux/clocksource.h>
  17 #include <linux/sched_clock.h>
  18 #include <linux/init.h>
  19
  20 #include <asm/ds1287.h>
  21 #include <asm/time.h>
  22 #include <asm/dec/ioasic.h>
  23 #include <asm/dec/ioasic_addrs.h>
  24
  25 static cycle_t dec_ioasic_hpt_read(struct clocksource *cs)
  26 {
  27         return ioasic_read(IO_REG_FCTR);
  28 }
  29
  30 static struct clocksource clocksource_dec = {
  31         .name           = "dec-ioasic",
  32         .read           = dec_ioasic_hpt_read,
  33         .mask           = CLOCKSOURCE_MASK(32),
  34         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  35 };
  36
  37 static u64 notrace dec_ioasic_read_sched_clock(void)
  38 {
  39         return ioasic_read(IO_REG_FCTR);
  40 }
  41
  42 int __init dec_ioasic_clocksource_init(void)
  43 {
  44         unsigned int freq;
  45         u32 start, end;
  46         int i = HZ / 8;
  47
  48         ds1287_timer_state();
  49         while (!ds1287_timer_state())
  50                 ;
  51
  52         start = dec_ioasic_hpt_read(&clocksource_dec);
  53
  54         while (i--)
  55                 while (!ds1287_timer_state())
  56                         ;
  57
  58         end = dec_ioasic_hpt_read(&clocksource_dec);
  59
  60         freq = (end - start) * 8;
  61
  62         /* An early revision of the I/O ASIC didn't have the counter.  */
  63         if (!freq)
  64                 return -ENXIO;
  65
  66         printk(KERN_INFO "I/O ASIC clock frequency %dHz\n", freq);
  67
  68         clocksource_dec.rating = 200 + freq / 10000000;
  69         clocksource_register_hz(&clocksource_dec, freq);
  70
  71         sched_clock_register(dec_ioasic_read_sched_clock, 32, freq);
  72
  73         return 0;
  74 }