[PATCH v2 1/3] cpufreq: CPPC: Keep the policy across CPU hotplug

[Sumit Gupta <sumitg@nvidia.com>]

Without online()/offline() callbacks, the cpufreq core fully tears
down a policy during exit() when its last online CPU is offlined,
and rebuilds it during init() when it comes back.

Add lightweight online()/offline() callbacks so the core instead
keeps the policy live and reuses the driver's cpu_data across
CPU hotplug. This avoids re-reading the CPPC capabilities on every
offline/online, making CPU hotplug faster.

Re-enable CPPC from online(), as it may have been disabled while
the CPU was offline.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index f6cea0c54dd9..432c6a6288a7 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -722,6 +722,31 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	return ret;
 }
 
+/*
+ * With offline() defined, the cpufreq core keeps the policy alive when
+ * a CPU is hotplugged out.
+ */
+static int cppc_cpufreq_cpu_offline(struct cpufreq_policy *policy)
+{
+	return 0;
+}
+
+/*
+ * Re-enable CPPC when the policy's CPU comes back online, since the platform
+ * may have disabled it while the CPU was offline.
+ */
+static int cppc_cpufreq_cpu_online(struct cpufreq_policy *policy)
+{
+	unsigned int cpu = policy->cpu;
+	int ret;
+
+	ret = cppc_set_enable(cpu, true);
+	if (ret && ret != -EOPNOTSUPP)
+		pr_warn("Failed to re-enable CPPC for CPU%d (%d)\n", cpu, ret);
+
+	return 0;
+}
+
 static void cppc_cpufreq_cpu_exit(struct cpufreq_policy *policy)
 {
 	struct cppc_cpudata *cpu_data = policy->driver_data;
@@ -1034,6 +1059,8 @@ static struct cpufreq_driver cppc_cpufreq_driver = {
 	.fast_switch = cppc_cpufreq_fast_switch,
 	.init = cppc_cpufreq_cpu_init,
 	.exit = cppc_cpufreq_cpu_exit,
+	.online = cppc_cpufreq_cpu_online,
+	.offline = cppc_cpufreq_cpu_offline,
 	.set_boost = cppc_cpufreq_set_boost,
 	.attr = cppc_cpufreq_attr,
 	.name = "cppc_cpufreq",
-- 
2.34.1