tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
36typedef 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 */
48static 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 */