diff options
| -rw-r--r-- | target/linux/generic/patches-3.10/307-mips-Reimplement-get_cycles.patch | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/target/linux/generic/patches-3.10/307-mips-Reimplement-get_cycles.patch b/target/linux/generic/patches-3.10/307-mips-Reimplement-get_cycles.patch new file mode 100644 index 0000000000..6a8f5b1bd5 --- /dev/null +++ b/target/linux/generic/patches-3.10/307-mips-Reimplement-get_cycles.patch @@ -0,0 +1,69 @@ +From 9c9b415c50bc298ac61412dff856eae2f54889ee Mon Sep 17 00:00:00 2001 +From: Ralf Baechle <ralf@linux-mips.org> +Date: Thu, 12 Sep 2013 13:47:32 +0200 +Subject: [PATCH] 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> +--- + arch/mips/include/asm/timex.h | 33 ++++++++++++++++++++++++++++++++- + 1 file changed, 32 insertions(+), 1 deletion(-) + +--- a/arch/mips/include/asm/timex.h ++++ b/arch/mips/include/asm/timex.h +@@ -10,6 +10,7 @@ + + #ifdef __KERNEL__ + ++#include <asm/cpu-features.h> + #include <asm/mipsregs.h> + + /* +@@ -33,9 +34,38 @@ + + 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 (cpu_data[0].cputype) { ++ 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__ */ |