diff options
Diffstat (limited to 'arch/mips/kernel/csrc-r4k.c')
| -rw-r--r-- | arch/mips/kernel/csrc-r4k.c | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c index e5ed7ada1433..1f910563fdf6 100644 --- a/arch/mips/kernel/csrc-r4k.c +++ b/arch/mips/kernel/csrc-r4k.c @@ -28,6 +28,43 @@ static u64 notrace r4k_read_sched_clock(void) return read_c0_count(); } +static inline unsigned int rdhwr_count(void) +{ + unsigned int count; + + __asm__ __volatile__( + " .set push\n" + " .set mips32r2\n" + " rdhwr %0, $2\n" + " .set pop\n" + : "=r" (count)); + + return count; +} + +static bool rdhwr_count_usable(void) +{ + unsigned int prev, curr, i; + + /* + * Older QEMUs have a broken implementation of RDHWR for the CP0 count + * which always returns a constant value. Try to identify this and don't + * use it in the VDSO if it is broken. This workaround can be removed + * once the fix has been in QEMU stable for a reasonable amount of time. + */ + for (i = 0, prev = rdhwr_count(); i < 100; i++) { + curr = rdhwr_count(); + + if (curr != prev) + return true; + + prev = curr; + } + + pr_warn("Not using R4K clocksource in VDSO due to broken RDHWR\n"); + return false; +} + int __init init_r4k_clocksource(void) { if (!cpu_has_counter || !mips_hpt_frequency) @@ -36,6 +73,13 @@ int __init init_r4k_clocksource(void) /* Calculate a somewhat reasonable rating value */ clocksource_mips.rating = 200 + mips_hpt_frequency / 10000000; + /* + * R2 onwards makes the count accessible to user mode so it can be used + * by the VDSO (HWREna is configured by configure_hwrena()). + */ + if (cpu_has_mips_r2_r6 && rdhwr_count_usable()) + clocksource_mips.archdata.vdso_clock_mode = VDSO_CLOCK_R4K; + clocksource_register_hz(&clocksource_mips, mips_hpt_frequency); sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency); |