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    Subject[PATCH v5 5/6] arm64: add hw_nmi_get_sample_period for preparation of lockup detector
    Date
    Set safe maximum CPU frequency to 5 GHz in case a particular platform
    doesn't implement cpufreq driver.
    Although, architecture doesn't put any restrictions on
    maximum frequency but 5 GHz seems to be safe maximum given the available
    Arm CPUs in the market which are clocked much less than 5 GHz.

    On the other hand, we can't make it much higher as it would lead to
    a large hard-lockup detection timeout on parts which are running
    slower (eg. 1GHz on Developerbox) and doesn't possess a cpufreq driver.

    [1]:http://lore.kernel.org/linux-arm-kernel/1610712101-14929-1-git-send-email-sumit.garg@linaro.org

    Co-developed-by: Sumit Garg <sumit.garg@linaro.org>
    Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
    Co-developed-by: Pingfan Liu <kernelfans@gmail.com>
    Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
    Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
    ---
    arch/arm64/kernel/Makefile | 1 +
    arch/arm64/kernel/watchdog_hld.c | 25 +++++++++++++++++++++++++
    2 files changed, 26 insertions(+)
    create mode 100644 arch/arm64/kernel/watchdog_hld.c

    diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
    index fa7981d0d917..303b69ad5366 100644
    --- a/arch/arm64/kernel/Makefile
    +++ b/arch/arm64/kernel/Makefile
    @@ -46,6 +46,7 @@ obj-$(CONFIG_MODULES) += module.o
    obj-$(CONFIG_ARM64_MODULE_PLTS) += module-plts.o
    obj-$(CONFIG_PERF_EVENTS) += perf_regs.o perf_callchain.o
    obj-$(CONFIG_HW_PERF_EVENTS) += perf_event.o
    +obj-$(CONFIG_HARDLOCKUP_DETECTOR_PERF) += watchdog_hld.o
    obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
    obj-$(CONFIG_CPU_PM) += sleep.o suspend.o
    obj-$(CONFIG_CPU_IDLE) += cpuidle.o
    diff --git a/arch/arm64/kernel/watchdog_hld.c b/arch/arm64/kernel/watchdog_hld.c
    new file mode 100644
    index 000000000000..de43318e4dd6
    --- /dev/null
    +++ b/arch/arm64/kernel/watchdog_hld.c
    @@ -0,0 +1,25 @@
    +// SPDX-License-Identifier: GPL-2.0
    +#include <linux/cpufreq.h>
    +
    +/*
    + * Safe maximum CPU frequency in case a particular platform doesn't implement
    + * cpufreq driver. Although, architecture doesn't put any restrictions on
    + * maximum frequency but 5 GHz seems to be safe maximum given the available
    + * Arm CPUs in the market which are clocked much less than 5 GHz. On the other
    + * hand, we can't make it much higher as it would lead to a large hard-lockup
    + * detection timeout on parts which are running slower (eg. 1GHz on
    + * Developerbox) and doesn't possess a cpufreq driver.
    + */
    +#define SAFE_MAX_CPU_FREQ 5000000000UL // 5 GHz
    +u64 hw_nmi_get_sample_period(int watchdog_thresh)
    +{
    + unsigned int cpu = smp_processor_id();
    + unsigned long max_cpu_freq;
    +
    + max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
    + if (!max_cpu_freq)
    + max_cpu_freq = SAFE_MAX_CPU_FREQ;
    +
    + return (u64)max_cpu_freq * watchdog_thresh;
    +}
    +
    --
    2.25.1
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