linux-kernel - [PATCH 1/2] thermal: power allocator: change the 'k

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Message-Id: <20201002122416.13659-2-lukasz.luba@arm.com>
Date:   Fri,  2 Oct 2020 13:24:15 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     daniel.lezcano@...aro.org, amitk@...nel.org,
        Dietmar.Eggemann@....com, lukasz.luba@....com
Subject: [PATCH 1/2] thermal: power allocator: change the 'k_i' coefficient estimation

Intelligent Power Allocation (IPA) is built around the PID controller
concept. The initialization code tries to setup the environment based on
the information available in DT or estimate the value based on minimum
power reported by each of the cooling device. The estimation will have an
impact on the PID controller behaviour via the related 'k_po', 'k_pu',
'k_i' coefficients and also on the power budget calculation.

This change prevents the situation when 'k_i' is relatively big compared
to 'k_po' and 'k_pu' values. This might happen when the estimation for
'sustainable_power' returned small value, thus 'k_po' and 'k_pu' are
small.

Signed-off-by: Lukasz Luba <lukasz.luba@....com>
---
 drivers/thermal/gov_power_allocator.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/thermal/gov_power_allocator.c b/drivers/thermal/gov_power_allocator.c
index 5cb518d8f156..f69fafe486a5 100644
--- a/drivers/thermal/gov_power_allocator.c
+++ b/drivers/thermal/gov_power_allocator.c
@@ -131,6 +131,7 @@ static void estimate_pid_constants(struct thermal_zone_device *tz,
 	int ret;
 	int switch_on_temp;
 	u32 temperature_threshold;
+	s32 k_i;

 	ret = tz->ops->get_trip_temp(tz, trip_switch_on, &switch_on_temp);
 	if (ret)
@@ -156,8 +157,11 @@ static void estimate_pid_constants(struct thermal_zone_device *tz,
 		tz->tzp->k_pu = int_to_frac(2 * sustainable_power) /
 			temperature_threshold;

-	if (!tz->tzp->k_i || force)
-		tz->tzp->k_i = int_to_frac(10) / 1000;
+	if (!tz->tzp->k_i || force) {
+		k_i = tz->tzp->k_pu / 10;
+		tz->tzp->k_i = k_i > 0 ? k_i : 1;
+	}
+
 	/*
 	 * The default for k_d and integral_cutoff is 0, so we can
 	 * leave them as they are.
-- 
2.17.1