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    Subject[PATCH v4 08/14] ACPI: add perf low power callback
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    This patch add an optional callback needed by some PMU features, e.g., AMD
    BRS, to give a chance to the perf_events code to change its state before
    going to low power and after coming back.

    The callback is void when the PERF_NEEDS_LOPWR_CB flag is not set.
    This flag must be set in arch specific perf_event.h header whenever needed.
    When not set, there is no impact of the ACPI code.

    Signed-off-by: Stephane Eranian <eranian@google.com>
    ---
    drivers/acpi/acpi_pad.c | 6 ++++++
    drivers/acpi/processor_idle.c | 5 +++++
    include/linux/perf_event.h | 6 ++++++
    3 files changed, 17 insertions(+)

    diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
    index f45979aa2d64..a306a07a60b5 100644
    --- a/drivers/acpi/acpi_pad.c
    +++ b/drivers/acpi/acpi_pad.c
    @@ -164,6 +164,9 @@ static int power_saving_thread(void *data)
    tsc_marked_unstable = 1;
    }
    local_irq_disable();
    +
    + perf_lopwr_cb(true);
    +
    tick_broadcast_enable();
    tick_broadcast_enter();
    stop_critical_timings();
    @@ -172,6 +175,9 @@ static int power_saving_thread(void *data)

    start_critical_timings();
    tick_broadcast_exit();
    +
    + perf_lopwr_cb(false);
    +
    local_irq_enable();

    if (time_before(expire_time, jiffies)) {
    diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
    index 76ef1bcc8848..7a3a613ae5ed 100644
    --- a/drivers/acpi/processor_idle.c
    +++ b/drivers/acpi/processor_idle.c
    @@ -20,6 +20,7 @@
    #include <linux/tick.h>
    #include <linux/cpuidle.h>
    #include <linux/cpu.h>
    +#include <linux/perf_event.h>
    #include <acpi/processor.h>

    /*
    @@ -546,6 +547,8 @@ static void wait_for_freeze(void)
    */
    static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx)
    {
    + perf_lopwr_cb(true);
    +
    if (cx->entry_method == ACPI_CSTATE_FFH) {
    /* Call into architectural FFH based C-state */
    acpi_processor_ffh_cstate_enter(cx);
    @@ -556,6 +559,8 @@ static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx)
    inb(cx->address);
    wait_for_freeze();
    }
    +
    + perf_lopwr_cb(false);
    }

    /**
    diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    index bbe02c80244b..f9760873e145 100644
    --- a/include/linux/perf_event.h
    +++ b/include/linux/perf_event.h
    @@ -1674,4 +1674,10 @@ typedef int (perf_snapshot_branch_stack_t)(struct perf_branch_entry *entries,
    unsigned int cnt);
    DECLARE_STATIC_CALL(perf_snapshot_branch_stack, perf_snapshot_branch_stack_t);

    +#ifndef PERF_NEEDS_LOPWR_CB
    +static inline void perf_lopwr_cb(bool mode)
    +{
    +}
    +#endif
    +
    #endif /* _LINUX_PERF_EVENT_H */
    --
    2.34.1.173.g76aa8bc2d0-goog
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