[PATCH v3 4/4] cpufreq: CPPC: Preserve OSPM-set registers across suspend/resume

[Sumit Gupta <sumitg@nvidia.com>]

The previous patch preserves the OSPM-set registers across CPU hotplug,
but system suspend/resume is a separate path. On platforms that reset
those registers or the performance controls across suspend, the values
are lost.

Reuse the same save/restore mechanism for suspend/resume:

  - suspend() only saves the current OSPM-set values. It does not revert
    them to firmware, since a later offline() already does that when
    system suspend offlines the secondary CPUs.
  - resume() needs the same steps as online(), so .resume points at
    online() directly.

Suggested-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 8a13ec49eb9d..be2d873ccd84 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -921,6 +921,22 @@ static int cppc_cpufreq_cpu_online(struct cpufreq_policy *policy)
 	return 0;
 }
 
+/*
+ * suspend() only saves the OSPM-set values. It does not revert them to the
+ * firmware values.
+ *
+ * This is because system suspend may later offline the secondary CPUs.
+ * That runs offline(), which saves the values and then reverts to firmware.
+ * If suspend() had already reverted, offline() would save the firmware value
+ * instead of the user's request, and the request would be lost.
+ */
+static int cppc_cpufreq_cpu_suspend(struct cpufreq_policy *policy)
+{
+	cppc_cpufreq_save_requested_regs(policy);
+
+	return 0;
+}
+
 static void cppc_cpufreq_cpu_exit(struct cpufreq_policy *policy)
 {
 	struct cppc_cpudata *cpu_data = policy->driver_data;
@@ -1235,6 +1251,8 @@ static struct cpufreq_driver cppc_cpufreq_driver = {
 	.exit = cppc_cpufreq_cpu_exit,
 	.online = cppc_cpufreq_cpu_online,
 	.offline = cppc_cpufreq_cpu_offline,
+	.suspend = cppc_cpufreq_cpu_suspend,
+	.resume = cppc_cpufreq_cpu_online,
 	.set_boost = cppc_cpufreq_set_boost,
 	.attr = cppc_cpufreq_attr,
 	.name = "cppc_cpufreq",
-- 
2.34.1