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From:   zhuguangqing83@gmail.com
To:     Amit Daniel Kachhap <amit.kachhap@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Javi Merino <javi.merino@kernel.org>,
        Zhang Rui <rui.zhang@intel.com>,
        Amit Kucheria <amitk@kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>
Cc:     linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Guangqing Zhu <zhuguangqing83@gmail.com>
Subject: [PATCH] thermal/drivers/cpuidle_cooling: Make sure that idle_duration is larger than residency
Date:   Fri,  2 Apr 2021 12:56:14 +0800
Message-Id: <20210402045615.22630-1-zhuguangqing83@gmail.com>
Precedence: bulk

From: Guangqing Zhu <zhuguangqing83@gmail.com>

The injected idle duration should be greater than the idle state min
residency, otherwise we end up consuming more energy and potentially invert
the mitigation effect.

In function __cpuidle_cooling_register(), if
of_property_read_u32(np, "exit-latency-us", &latency_us) is failed, then
maybe we should not use latency_us. In this case, a zero latency_us for
forced_idle_latency_limit_ns is better than UMAX_INT. It means to use
governors in the usual way.

Signed-off-by: Guangqing Zhu <zhuguangqing83@gmail.com>
---
 drivers/powercap/idle_inject.c    | 1 -
 drivers/thermal/cpuidle_cooling.c | 8 +++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c
index 6e1a0043c411..d76eef1e9387 100644
--- a/drivers/powercap/idle_inject.c
+++ b/drivers/powercap/idle_inject.c
@@ -309,7 +309,6 @@ struct idle_inject_device *idle_inject_register(struct cpumask *cpumask)
 	cpumask_copy(to_cpumask(ii_dev->cpumask), cpumask);
 	hrtimer_init(&ii_dev->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	ii_dev->timer.function = idle_inject_timer_fn;
-	ii_dev->latency_us = UINT_MAX;
 
 	for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) {
 
diff --git a/drivers/thermal/cpuidle_cooling.c b/drivers/thermal/cpuidle_cooling.c
index 7ecab4b16b29..de770eb5b2ba 100644
--- a/drivers/thermal/cpuidle_cooling.c
+++ b/drivers/thermal/cpuidle_cooling.c
@@ -175,7 +175,8 @@ static int __cpuidle_cooling_register(struct device_node *np,
 	struct cpuidle_cooling_device *idle_cdev;
 	struct thermal_cooling_device *cdev;
 	unsigned int idle_duration_us = TICK_USEC;
-	unsigned int latency_us = UINT_MAX;
+	unsigned int latency_us = 0;
+	unsigned int residency_us = UINT_MAX;
 	char dev_name[THERMAL_NAME_LENGTH];
 	int id, ret;
 
@@ -199,6 +200,11 @@ static int __cpuidle_cooling_register(struct device_node *np,
 
 	of_property_read_u32(np, "duration-us", &idle_duration_us);
 	of_property_read_u32(np, "exit-latency-us", &latency_us);
+	of_property_read_u32(np, "min-residency-us", &residency_us);
+	if (idle_duration_us <= residency_us) {
+		ret = -EINVAL;
+		goto out_unregister;
+	}
 
 	idle_inject_set_duration(ii_dev, TICK_USEC, idle_duration_us);
 	idle_inject_set_latency(ii_dev, latency_us);
-- 
2.17.1