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 * Standard way to access the cycle counter. 23 * Currently only used on SMP for scheduling. 24 * 25 * Only the low 32 bits are available as a continuously counting entity. 26 * But this only means we'll force a reschedule every 8 seconds or so, 27 * which isn't an evil thing. 28 * 29 * We know that all SMP capable CPUs have cycle counters. 30 */ 31 32 typedef unsigned int cycles_t; 33 34 /* 35 * On R4000/R4400 an erratum exists such that if the cycle counter is 36 * read in the exact moment that it is matching the compare register, 37 * no interrupt will be generated. 38 * 39 * There is a suggested workaround and also the erratum can't strike if 40 * the compare interrupt isn't being used as the clock source device. 41 * However for now the implementation of this function doesn't get these 42 * fine details right. 43 */ 44 static inline int can_use_mips_counter(unsigned int prid) 45 { 46 int comp = (prid & PRID_COMP_MASK) != PRID_COMP_LEGACY; 47 48 if (__builtin_constant_p(cpu_has_counter) && !cpu_has_counter) 49 return 0; 50 else if (__builtin_constant_p(cpu_has_mips_r) && cpu_has_mips_r) 51 return 1; 52 else if (likely(!__builtin_constant_p(cpu_has_mips_r) && comp)) 53 return 1; 54 /* Make sure we don't peek at cpu_data[0].options in the fast path! */ 55 if (!__builtin_constant_p(cpu_has_counter)) 56 asm volatile("" : "=m" (cpu_data[0].options)); 57 if (likely(cpu_has_counter && 58 prid > (PRID_IMP_R4000 | PRID_REV_ENCODE_44(15, 15)))) 59 return 1; 60 else 61 return 0; 62 } 63 64 static inline cycles_t get_cycles(void) 65 { 66 if (can_use_mips_counter(read_c0_prid())) 67 return read_c0_count(); 68 else 69 return 0; /* no usable counter */ 70 } 71 #define get_cycles get_cycles 72 73 /* 74 * Like get_cycles - but where c0_count is not available we desperately 75 * use c0_random in an attempt to get at least a little bit of entropy. 76 */ 77 static inline unsigned long random_get_entropy(void) 78 { 79 unsigned int c0_random; 80 81 if (can_use_mips_counter(read_c0_prid())) 82 return read_c0_count(); 83 84 if (cpu_has_3kex) 85 c0_random = (read_c0_random() >> 8) & 0x3f; 86 else 87 c0_random = read_c0_random() & 0x3f; 88 return (random_get_entropy_fallback() << 6) | (0x3f - c0_random); 89 } 90 #define random_get_entropy random_get_entropy 91 92 #endif /* __KERNEL__ */ 93 94 #endif /* _ASM_TIMEX_H */ 95