arch/mips/include/asm/timex.h

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 1998, 1999, 2003 by Ralf Baechle
   7  */
   8 #ifndef _ASM_TIMEX_H
   9 #define _ASM_TIMEX_H
  10
  11 #ifdef __KERNEL__
  12
  13 #include <asm/cpu-features.h>
  14 #include <asm/mipsregs.h>
  15 #include <asm/cpu-type.h>
  16
  17 /*
  18  * This is the clock rate of the i8253 PIT.  A MIPS system may not have
  19  * a PIT by the symbol is used all over the kernel including some APIs.
  20  * So keeping it defined to the number for the PIT is the only sane thing
  21  * for now.
  22  */
  23 #define CLOCK_TICK_RATE 1193182
  24
  25 /*
  26  * Standard way to access the cycle counter.
  27  * Currently only used on SMP for scheduling.
  28  *
  29  * Only the low 32 bits are available as a continuously counting entity.
  30  * But this only means we'll force a reschedule every 8 seconds or so,
  31  * which isn't an evil thing.
  32  *
  33  * We know that all SMP capable CPUs have cycle counters.
  34  */
  35
  36 typedef unsigned int cycles_t;
  37
  38 /*
  39  * On R4000/R4400 before version 5.0 an erratum exists such that if the
  40  * cycle counter is read in the exact moment that it is matching the
  41  * compare register, no interrupt will be generated.
  42  *
  43  * There is a suggested workaround and also the erratum can't strike if
  44  * the compare interrupt isn't being used as the clock source device.
  45  * However for now the implementaton of this function doesn't get these
  46  * fine details right.
  47  */
  48 static inline cycles_t get_cycles(void)
  49 {
  50         switch (boot_cpu_type()) {
  51         case CPU_R4400PC:
  52         case CPU_R4400SC:
  53         case CPU_R4400MC:
  54                 if ((read_c0_prid() & 0xff) >= 0x0050)
  55                         return read_c0_count();
  56                 break;
  57
  58         case CPU_R4000PC:
  59         case CPU_R4000SC:
  60         case CPU_R4000MC:
  61                 break;
  62
  63         default:
  64                 if (cpu_has_counter)
  65                         return read_c0_count();
  66                 break;
  67         }
  68
  69         return 0;       /* no usable counter */
  70 }
  71
  72 #endif /* __KERNEL__ */
  73
  74 #endif /*  _ASM_TIMEX_H */