diff options
| author | Ralf Baechle <ralf@linux-mips.org> | 2013-09-12 13:47:32 +0200 |
|---|---|---|
| committer | Ralf Baechle <ralf@linux-mips.org> | 2013-09-18 16:31:49 +0200 |
| commit | 9c9b415c50bc298ac61412dff856eae2f54889ee (patch) | |
| tree | b2fd1afaf7740202cd99d37ff0084dcd87674e46 /arch | |
| parent | 69f24d1784b631b81a54eb57c49bf46536dd2382 (diff) | |
MIPS: Reimplement get_cycles().
This essentially reverts commit efb9ca08b5a2374b29938cdcab417ce4feb14b54
(kernel.org) / 58020a106879a8b372068741c81f0015c9b0b96dbv [[MIPS] Change
get_cycles to always return 0.]
Most users of get_cycles() invoke it as a timing interface. That's why
in modern kernels it was never very much missed for. /dev/random however
uses get_cycles() in the how the jitter in the interrupt timing contains
some useful entropy.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/mips/include/asm/timex.h | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/arch/mips/include/asm/timex.h b/arch/mips/include/asm/timex.h index 6529704aa73..c5424757da6 100644 --- a/arch/mips/include/asm/timex.h +++ b/arch/mips/include/asm/timex.h @@ -10,7 +10,9 @@ #ifdef __KERNEL__ +#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 @@ -33,9 +35,38 @@ 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 cycles_t get_cycles(void) { - return 0; + switch (boot_cpu_type()) { + case CPU_R4400PC: + case CPU_R4400SC: + case CPU_R4400MC: + if ((read_c0_prid() & 0xff) >= 0x0050) + return read_c0_count(); + break; + + case CPU_R4000PC: + case CPU_R4000SC: + case CPU_R4000MC: + break; + + default: + if (cpu_has_counter) + return read_c0_count(); + break; + } + + return 0; /* no usable counter */ } #endif /* __KERNEL__ */ |