arch/arm/plat-versatile/sched-clock.c

   1 /*
   2  *  linux/arch/arm/plat-versatile/sched-clock.c
   3  *
   4  *  Copyright (C) 1999 - 2003 ARM Limited
   5  *  Copyright (C) 2000 Deep Blue Solutions Ltd
   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 #include <linux/cnt32_to_63.h>
  22 #include <linux/io.h>
  23 #include <linux/sched.h>
  24 #include <asm/div64.h>
  25
  26 #include <mach/hardware.h>
  27 #include <mach/platform.h>
  28
  29 #ifdef VERSATILE_SYS_BASE
  30 #define REFCOUNTER      (__io_address(VERSATILE_SYS_BASE) + VERSATILE_SYS_24MHz_OFFSET)
  31 #endif
  32
  33 #ifdef REALVIEW_SYS_BASE
  34 #define REFCOUNTER      (__io_address(REALVIEW_SYS_BASE) + REALVIEW_SYS_24MHz_OFFSET)
  35 #endif
  36
  37 /*
  38  * This is the Realview and Versatile sched_clock implementation.  This
  39  * has a resolution of 41.7ns, and a maximum value of about 35583 days.
  40  *
  41  * The return value is guaranteed to be monotonic in that range as
  42  * long as there is always less than 89 seconds between successive
  43  * calls to this function.
  44  */
  45 unsigned long long sched_clock(void)
  46 {
  47         unsigned long long v = cnt32_to_63(readl(REFCOUNTER));
  48
  49         /* the <<1 gets rid of the cnt_32_to_63 top bit saving on a bic insn */
  50         v *= 125<<1;
  51         do_div(v, 3<<1);
  52
  53         return v;
  54 }