[PATCH v2] cpufreq: Fix per-policy boost behavior after CPU hotplug

[PoShao Chen <poshao.chen@mediatek.com>]

This patch fixes the behavior of the cpufreq boost when the
global boost flag is toggled during CPU hotplug offline. This action
previously led to incorrect scaling_max_freq values when the CPU was
brought back online. The issue also manifested as incorrect
scaling_cur_freq under the performance governor.

For example, after the following operations, even if the global boost
is disabled, the resulting scaling_max_freq and scaling_cur_freq
will still reflect the settings of an enabled boost.

$ echo performance > /sys/devices/system/cpu/cpufreq/policy7/scaling_governor
$ cat /sys/devices/system/cpu/cpufreq/policy7/scaling_cur_freq
3200000
$ cat /sys/devices/system/cpu/cpufreq/policy7/scaling_max_freq
3200000

$ echo 1 > /sys/devices/system/cpu/cpufreq/boost
$ cat /sys/devices/system/cpu/cpufreq/policy7/scaling_cur_freq
3250000
$ cat /sys/devices/system/cpu/cpufreq/policy7/scaling_max_freq
3250000

$ echo 0 > /sys/devices/system/cpu/cpu7/online
$ echo 0 > /sys/devices/system/cpu/cpufreq/boost
$ echo 1 > /sys/devices/system/cpu/cpu7/online
$ cat /sys/devices/system/cpu/cpufreq/policy7/scaling_cur_freq
3250000
$ cat /sys/devices/system/cpu/cpufreq/policy7/scaling_max_freq
3250000

Signed-off-by: PoShao Chen <poshao.chen@mediatek.com>

---
V1 -> V2: Adjusted log messages and fixed build error.

Link:
  https://lore.kernel.org/all/20240611115920.28665-1-poshao.chen@mediatek.com/
---
 drivers/cpufreq/cpufreq.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index a45aac17c20f..faadae05bc8a 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1495,6 +1495,35 @@ static int cpufreq_online(unsigned int cpu)
 
 		blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
 				CPUFREQ_CREATE_POLICY, policy);
+	} else {
+		/*
+		 * Call freq_qos_update_request() for the per-policy boost flag mirror
+		 * the cpufreq_driver boost during hotplug online.
+		 * Register an online callback if the default mirroring of the global
+		 * boost setting is not intended.
+		 */
+		if (!cpufreq_driver->online) {
+			ret = freq_qos_update_request(policy->max_freq_req, policy->max);
+			if (ret)
+				pr_err("%s: freq qos update failed\n", __func__);
+		} else {
+			/*
+			 * Let the per-policy boost flag mirror the cpufreq_driver
+			 * boost if an illegal state occurs after hotplug
+			 */
+			if (policy->boost_enabled && !cpufreq_driver->boost_enabled) {
+				pr_info("%s: local boost flag mirror the global boost\n",
+					__func__);
+				policy->boost_enabled = cpufreq_driver->boost_enabled;
+				ret = cpufreq_driver->set_boost(policy,
+							cpufreq_driver->boost_enabled);
+				if (ret) {
+					policy->boost_enabled = !policy->boost_enabled;
+					pr_err("%s: Failed to mirror the global boost flag\n",
+					       __func__);
+				}
+			}
+		}
 	}
 
 	if (cpufreq_driver->get && has_target()) {
-- 
2.18.0