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 * Copyright (C) 2014 by Maciej W. Rozycki
  8 */
  9#ifndef _ASM_TIMEX_H
 10#define _ASM_TIMEX_H
 11
 12#ifdef __KERNEL__
 13
 14#include <linux/compiler.h>
 15
 16#include <asm/cpu.h>
 17#include <asm/cpu-features.h>
 18#include <asm/mipsregs.h>
 19#include <asm/cpu-type.h>
 20
 21/*
 22 * This is the clock rate of the i8253 PIT.  A MIPS system may not have
 23 * a PIT by the symbol is used all over the kernel including some APIs.
 24 * So keeping it defined to the number for the PIT is the only sane thing
 25 * for now.
 26 */
 27#define CLOCK_TICK_RATE 1193182
 28
 29/*
 30 * Standard way to access the cycle counter.
 31 * Currently only used on SMP for scheduling.
 32 *
 33 * Only the low 32 bits are available as a continuously counting entity.
 34 * But this only means we'll force a reschedule every 8 seconds or so,
 35 * which isn't an evil thing.
 36 *
 37 * We know that all SMP capable CPUs have cycle counters.
 38 */
 39
 40typedef unsigned int cycles_t;
 41
 42/*
 43 * On R4000/R4400 before version 5.0 an erratum exists such that if the
 44 * cycle counter is read in the exact moment that it is matching the
 45 * compare register, no interrupt will be generated.
 46 *
 47 * There is a suggested workaround and also the erratum can't strike if
 48 * the compare interrupt isn't being used as the clock source device.
 49 * However for now the implementaton of this function doesn't get these
 50 * fine details right.
 51 */
 52static inline int can_use_mips_counter(unsigned int prid)
 53{
 54	int comp = (prid & PRID_COMP_MASK) != PRID_COMP_LEGACY;
 55
 56	if (__builtin_constant_p(cpu_has_counter) && !cpu_has_counter)
 57		return 0;
 58	else if (__builtin_constant_p(cpu_has_mips_r) && cpu_has_mips_r)
 59		return 1;
 60	else if (likely(!__builtin_constant_p(cpu_has_mips_r) && comp))
 61		return 1;
 62	/* Make sure we don't peek at cpu_data[0].options in the fast path! */
 63	if (!__builtin_constant_p(cpu_has_counter))
 64		asm volatile("" : "=m" (cpu_data[0].options));
 65	if (likely(cpu_has_counter &&
 66		   prid >= (PRID_IMP_R4000 | PRID_REV_ENCODE_44(5, 0))))
 67		return 1;
 68	else
 69		return 0;
 70}
 71
 72static inline cycles_t get_cycles(void)
 73{
 74	if (can_use_mips_counter(read_c0_prid()))
 75		return read_c0_count();
 76	else
 77		return 0;	/* no usable counter */
 78}
 
 79
 80/*
 81 * Like get_cycles - but where c0_count is not available we desperately
 82 * use c0_random in an attempt to get at least a little bit of entropy.
 83 *
 84 * R6000 and R6000A neither have a count register nor a random register.
 85 * That leaves no entropy source in the CPU itself.
 86 */
 87static inline unsigned long random_get_entropy(void)
 88{
 89	unsigned int prid = read_c0_prid();
 90	unsigned int imp = prid & PRID_IMP_MASK;
 91
 92	if (can_use_mips_counter(prid))
 93		return read_c0_count();
 94	else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A))
 95		return read_c0_random();
 
 96	else
 97		return 0;	/* no usable register */
 
 98}
 99#define random_get_entropy random_get_entropy
100
101#endif /* __KERNEL__ */
102
103#endif /*  _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 * Copyright (C) 2014 by Maciej W. Rozycki
  8 */
  9#ifndef _ASM_TIMEX_H
 10#define _ASM_TIMEX_H
 11
 12#ifdef __KERNEL__
 13
 14#include <linux/compiler.h>
 15
 16#include <asm/cpu.h>
 17#include <asm/cpu-features.h>
 18#include <asm/mipsregs.h>
 19#include <asm/cpu-type.h>
 20
 21/*
 22 * This is the clock rate of the i8253 PIT.  A MIPS system may not have
 23 * a PIT by the symbol is used all over the kernel including some APIs.
 24 * So keeping it defined to the number for the PIT is the only sane thing
 25 * for now.
 26 */
 27#define CLOCK_TICK_RATE 1193182
 28
 29/*
 30 * Standard way to access the cycle counter.
 31 * Currently only used on SMP for scheduling.
 32 *
 33 * Only the low 32 bits are available as a continuously counting entity.
 34 * But this only means we'll force a reschedule every 8 seconds or so,
 35 * which isn't an evil thing.
 36 *
 37 * We know that all SMP capable CPUs have cycle counters.
 38 */
 39
 40typedef unsigned int cycles_t;
 41
 42/*
 43 * On R4000/R4400 an erratum exists such that if the cycle counter is
 44 * read in the exact moment that it is matching the compare register,
 45 * no interrupt will be generated.
 46 *
 47 * There is a suggested workaround and also the erratum can't strike if
 48 * the compare interrupt isn't being used as the clock source device.
 49 * However for now the implementaton of this function doesn't get these
 50 * fine details right.
 51 */
 52static inline int can_use_mips_counter(unsigned int prid)
 53{
 54	int comp = (prid & PRID_COMP_MASK) != PRID_COMP_LEGACY;
 55
 56	if (__builtin_constant_p(cpu_has_counter) && !cpu_has_counter)
 57		return 0;
 58	else if (__builtin_constant_p(cpu_has_mips_r) && cpu_has_mips_r)
 59		return 1;
 60	else if (likely(!__builtin_constant_p(cpu_has_mips_r) && comp))
 61		return 1;
 62	/* Make sure we don't peek at cpu_data[0].options in the fast path! */
 63	if (!__builtin_constant_p(cpu_has_counter))
 64		asm volatile("" : "=m" (cpu_data[0].options));
 65	if (likely(cpu_has_counter &&
 66		   prid > (PRID_IMP_R4000 | PRID_REV_ENCODE_44(15, 15))))
 67		return 1;
 68	else
 69		return 0;
 70}
 71
 72static inline cycles_t get_cycles(void)
 73{
 74	if (can_use_mips_counter(read_c0_prid()))
 75		return read_c0_count();
 76	else
 77		return 0;	/* no usable counter */
 78}
 79#define get_cycles get_cycles
 80
 81/*
 82 * Like get_cycles - but where c0_count is not available we desperately
 83 * use c0_random in an attempt to get at least a little bit of entropy.
 
 
 
 84 */
 85static inline unsigned long random_get_entropy(void)
 86{
 87	unsigned int c0_random;
 
 88
 89	if (can_use_mips_counter(read_c0_prid()))
 90		return read_c0_count();
 91
 92	if (cpu_has_3kex)
 93		c0_random = (read_c0_random() >> 8) & 0x3f;
 94	else
 95		c0_random = read_c0_random() & 0x3f;
 96	return (random_get_entropy_fallback() << 6) | (0x3f - c0_random);
 97}
 98#define random_get_entropy random_get_entropy
 99
100#endif /* __KERNEL__ */
101
102#endif /*  _ASM_TIMEX_H */