cpuidle: coupled: add parallel barrier function

[firefly-linux-kernel-4.4.55.git] / drivers / cpuidle / coupled.c

diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
index aab6bba8daec75842acf76ffb01f7099a2bd60ee..2c9bf2692232e51a66e5455368d9881383ccfc2f 100644 (file)
--- a/drivers/cpuidle/coupled.c
+++ b/drivers/cpuidle/coupled.c
@@ -129,6 +129,43 @@ 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