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 implementation 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 */
103