diff options
Diffstat (limited to 'arch/mips/include/asm/timex.h')
| -rw-r--r-- | arch/mips/include/asm/timex.h | 62 |
1 files changed, 61 insertions, 1 deletions
diff --git a/arch/mips/include/asm/timex.h b/arch/mips/include/asm/timex.h index 6529704aa73..b05bb70a2e4 100644 --- a/arch/mips/include/asm/timex.h +++ b/arch/mips/include/asm/timex.h @@ -4,13 +4,19 @@ * 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 @@ -33,10 +39,64 @@ typedef unsigned int cycles_t; +/* + * On R4000/R4400 before version 5.0 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(5, 0)))) + return 1; + else + return 0; +} + static inline cycles_t get_cycles(void) { - return 0; + if (can_use_mips_counter(read_c0_prid())) + return read_c0_count(); + else + return 0; /* no usable counter */ +} + +/* + * 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. + * + * R6000 and R6000A neither have a count register nor a random register. + * That leaves no entropy source in the CPU itself. + */ +static inline unsigned long random_get_entropy(void) +{ + unsigned int prid = read_c0_prid(); + unsigned int imp = prid & PRID_IMP_MASK; + + if (can_use_mips_counter(prid)) + return read_c0_count(); + else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A)) + return read_c0_random(); + else + return 0; /* no usable register */ } +#define random_get_entropy random_get_entropy #endif /* __KERNEL__ */ |