ARM: bL_switcher: hot-unplug half of the available CPUs

With an MP kernel, all the CPUs are initially available.  The switcher
model always uses half of them at any time.  Let's remove half of the
available CPUs and make sure we still have a working switcher
configuration.

Signed-off-by: Nicolas Pitre <nico@linaro.org>

1 files changed, 77 insertions, 1 deletions

diff --git a/arch/arm/common/bL_switcher.c b/arch/arm/common/bL_switcher.c
index eeee8536da9..46048347379 100644
--- a/arch/arm/common/bL_switcher.c
+++ b/arch/arm/common/bL_switcher.c
@@ -297,18 +297,94 @@ int bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)
 
 EXPORT_SYMBOL_GPL(bL_switch_request);
 
+/*
+ * Activation and configuration code.
+ */
+
+static cpumask_t bL_switcher_removed_logical_cpus;
+
+static void __init bL_switcher_restore_cpus(void)
+{
+	int i;
+
+	for_each_cpu(i, &bL_switcher_removed_logical_cpus)
+		cpu_up(i);
+}
+
+static int __init bL_switcher_halve_cpus(void)
+{
+	int cpu, cluster, i, ret;
+	cpumask_t cluster_mask[2], common_mask;
+
+	cpumask_clear(&bL_switcher_removed_logical_cpus);
+	cpumask_clear(&cluster_mask[0]);
+	cpumask_clear(&cluster_mask[1]);
+
+	for_each_online_cpu(i) {
+		cpu = cpu_logical_map(i) & 0xff;
+		cluster = (cpu_logical_map(i) >> 8) & 0xff;
+		if (cluster >= 2) {
+			pr_err("%s: only dual cluster systems are supported\n", __func__);
+			return -EINVAL;
+		}
+		cpumask_set_cpu(cpu, &cluster_mask[cluster]);
+	}
+
+	if (!cpumask_and(&common_mask, &cluster_mask[0], &cluster_mask[1])) {
+		pr_err("%s: no common set of CPUs\n", __func__);
+		return -EINVAL;
+	}
+
+	for_each_online_cpu(i) {
+		cpu = cpu_logical_map(i) & 0xff;
+		cluster = (cpu_logical_map(i) >> 8) & 0xff;
+
+		if (cpumask_test_cpu(cpu, &common_mask)) {
+			/*
+			 * We keep only those logical CPUs which number
+			 * is equal to their physical CPU number. This is
+			 * not perfect but good enough in most cases.
+			 */
+			if (cpu == i)
+				continue;
+		}
+
+		ret = cpu_down(i);
+		if (ret) {
+			bL_switcher_restore_cpus();
+			return ret;
+		}
+		cpumask_set_cpu(i, &bL_switcher_removed_logical_cpus);
+	}
+
+	return 0;
+}
+
 static int __init bL_switcher_init(void)
 {
-	int cpu;
+	int cpu, ret;
 
 	pr_info("big.LITTLE switcher initializing\n");
 
+	if (MAX_NR_CLUSTERS != 2) {
+		pr_err("%s: only dual cluster systems are supported\n", __func__);
+		return -EINVAL;
+	}
+
+	cpu_hotplug_driver_lock();
+	ret = bL_switcher_halve_cpus();
+	if (ret) {
+		cpu_hotplug_driver_unlock();
+		return ret;
+	}
+
 	for_each_online_cpu(cpu) {
 		struct bL_thread *t = &bL_threads[cpu];
 		init_waitqueue_head(&t->wq);
 		t->wanted_cluster = -1;
 		t->task = bL_switcher_thread_create(cpu, t);
 	}
+	cpu_hotplug_driver_unlock();
 
 	pr_info("big.LITTLE switcher initialized\n");
 	return 0;