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    Subject[PATCH 18/52] cpuidle: coupled: add parallel barrier function
    Date
    From: Colin Cross <ccross@android.com>

    Adds cpuidle_coupled_parallel_barrier, which can be used by coupled
    cpuidle state enter functions to handle resynchronization after
    determining if any cpu needs to abort. The normal use case will
    be:

    static bool abort_flag;
    static atomic_t abort_barrier;

    int arch_cpuidle_enter(struct cpuidle_device *dev, ...)
    {
    if (arch_turn_off_irq_controller()) {
    /* returns an error if an irq is pending and would be lost
    if idle continued and turned off power */
    abort_flag = true;
    }

    cpuidle_coupled_parallel_barrier(dev, &abort_barrier);

    if (abort_flag) {
    /* One of the cpus didn't turn off it's irq controller */
    arch_turn_on_irq_controller();
    return -EINTR;
    }

    /* continue with idle */
    ...
    }

    This will cause all cpus to abort idle together if one of them needs
    to abort.

    Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
    Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
    Reviewed-by: Kevin Hilman <khilman@ti.com>
    Tested-by: Kevin Hilman <khilman@ti.com>
    Signed-off-by: Colin Cross <ccross@android.com>
    Signed-off-by: Len Brown <len.brown@intel.com>
    ---
    drivers/cpuidle/coupled.c | 37 +++++++++++++++++++++++++++++++++++++
    include/linux/cpuidle.h | 4 ++++
    2 files changed, 41 insertions(+)

    diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
    index aab6bba..2c9bf26 100644
    --- a/drivers/cpuidle/coupled.c
    +++ b/drivers/cpuidle/coupled.c
    @@ -130,6 +130,43 @@ static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb);
    static cpumask_t cpuidle_coupled_poked_mask;

    /**
    + * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus
    + * @dev: cpuidle_device of the calling cpu
    + * @a: atomic variable to hold the barrier
    + *
    + * No caller to this function will return from this function until all online
    + * cpus in the same coupled group have called this function. Once any caller
    + * has returned from this function, the barrier is immediately available for
    + * reuse.
    + *
    + * The atomic variable a must be initialized to 0 before any cpu calls
    + * this function, will be reset to 0 before any cpu returns from this function.
    + *
    + * Must only be called from within a coupled idle state handler
    + * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).
    + *
    + * Provides full smp barrier semantics before and after calling.
    + */
    +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)
    +{
    + int n = dev->coupled->online_count;
    +
    + smp_mb__before_atomic_inc();
    + atomic_inc(a);
    +
    + while (atomic_read(a) < n)
    + cpu_relax();
    +
    + if (atomic_inc_return(a) == n * 2) {
    + atomic_set(a, 0);
    + return;
    + }
    +
    + while (atomic_read(a) > n)
    + cpu_relax();
    +}
    +
    +/**
    * cpuidle_state_is_coupled - check if a state is part of a coupled set
    * @dev: struct cpuidle_device for the current cpu
    * @drv: struct cpuidle_driver for the platform
    diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
    index 6038448..5ab7183 100644
    --- a/include/linux/cpuidle.h
    +++ b/include/linux/cpuidle.h
    @@ -183,6 +183,10 @@ static inline int cpuidle_play_dead(void) {return -ENODEV; }

    #endif

    +#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
    +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a);
    +#endif
    +
    /******************************
    * CPUIDLE GOVERNOR INTERFACE *
    ******************************/
    --
    1.7.12.rc0


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