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/* * This file is subject to the terms and conditions of the GNU General Public * License. See the file "COPYING" in the main directory of this archive * for more details. * * Copyright (C) 1998, 1999, 2003 by Ralf Baechle * Copyright (C) 2014 by Maciej W. Rozycki */ #ifndef _ASM_TIMEX_H #define _ASM_TIMEX_H #ifdef __KERNEL__ #include <linux/compiler.h> #include <asm/cpu.h> #include <asm/cpu-features.h> #include <asm/mipsregs.h> #include <asm/cpu-type.h> /* * This is the clock rate of the i8253 PIT. A MIPS system may not have * a PIT by the symbol is used all over the kernel including some APIs. * So keeping it defined to the number for the PIT is the only sane thing * for now. */ #define CLOCK_TICK_RATE 1193182 /* * Standard way to access the cycle counter. * Currently only used on SMP for scheduling. * * Only the low 32 bits are available as a continuously counting entity. * But this only means we'll force a reschedule every 8 seconds or so, * which isn't an evil thing. * * We know that all SMP capable CPUs have cycle counters. */ typedef unsigned int cycles_t; /* * On R4000/R4400 an erratum exists such that if the cycle counter is * read in the exact moment that it is matching the compare register, * no interrupt will be generated. * * There is a suggested workaround and also the erratum can't strike if * the compare interrupt isn't being used as the clock source device. * However for now the implementaton of this function doesn't get these * fine details right. */ static inline int can_use_mips_counter(unsigned int prid) { int comp = (prid & PRID_COMP_MASK) != PRID_COMP_LEGACY; if (__builtin_constant_p(cpu_has_counter) && !cpu_has_counter) return 0; else if (__builtin_constant_p(cpu_has_mips_r) && cpu_has_mips_r) return 1; else if (likely(!__builtin_constant_p(cpu_has_mips_r) && comp)) return 1; /* Make sure we don't peek at cpu_data[0].options in the fast path! */ if (!__builtin_constant_p(cpu_has_counter)) asm volatile("" : "=m" (cpu_data[0].options)); if (likely(cpu_has_counter && prid > (PRID_IMP_R4000 | PRID_REV_ENCODE_44(15, 15)))) return 1; else return 0; } static inline cycles_t get_cycles(void) { if (can_use_mips_counter(read_c0_prid())) return read_c0_count(); else return 0; /* no usable counter */ } #define get_cycles get_cycles /* * Like get_cycles - but where c0_count is not available we desperately * use c0_random in an attempt to get at least a little bit of entropy. */ static inline unsigned long random_get_entropy(void) { unsigned int c0_random; if (can_use_mips_counter(read_c0_prid())) return read_c0_count(); if (cpu_has_3kex) c0_random = (read_c0_random() >> 8) & 0x3f; else c0_random = read_c0_random() & 0x3f; return (random_get_entropy_fallback() << 6) | (0x3f - c0_random); } #define random_get_entropy random_get_entropy #endif /* __KERNEL__ */ #endif /* _ASM_TIMEX_H */
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