From aa1a43262ad5df010768f69530fa179ff81651d3 Mon Sep 17 00:00:00 2001
From: Vincent Donnefort <vincent.donnefort@arm.com>
Date: Wed, 8 Sep 2021 15:05:22 +0100
Subject: [PATCH] PM: EM: Fix inefficient states detection
Git-commit: aa1a43262ad5df010768f69530fa179ff81651d3
Patch-mainline: v5.16-rc1
References: git-fixes stable-5.14.19

Currently, a debug message is printed if an inefficient state is detected
in the Energy Model. Unfortunately, it won't detect if the first state is
inefficient or if two successive states are. Fix this behavior.

Fixes: 27871f7a8a34 (PM: Introduce an Energy Model management framework)
Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 kernel/power/energy_model.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
index a332ccd829e2..97e62469a6b3 100644
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -107,8 +107,7 @@ static void em_debug_remove_pd(struct device *dev) {}
 static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
 				int nr_states, struct em_data_callback *cb)
 {
-	unsigned long opp_eff, prev_opp_eff = ULONG_MAX;
-	unsigned long power, freq, prev_freq = 0;
+	unsigned long power, freq, prev_freq = 0, prev_cost = ULONG_MAX;
 	struct em_perf_state *table;
 	int i, ret;
 	u64 fmax;
@@ -153,27 +152,21 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
 
 		table[i].power = power;
 		table[i].frequency = prev_freq = freq;
-
-		/*
-		 * The hertz/watts efficiency ratio should decrease as the
-		 * frequency grows on sane platforms. But this isn't always
-		 * true in practice so warn the user if a higher OPP is more
-		 * power efficient than a lower one.
-		 */
-		opp_eff = freq / power;
-		if (opp_eff >= prev_opp_eff)
-			dev_dbg(dev, "EM: hertz/watts ratio non-monotonically decreasing: em_perf_state %d >= em_perf_state%d\n",
-					i, i - 1);
-		prev_opp_eff = opp_eff;
 	}
 
 	/* Compute the cost of each performance state. */
 	fmax = (u64) table[nr_states - 1].frequency;
-	for (i = 0; i < nr_states; i++) {
+	for (i = nr_states - 1; i >= 0; i--) {
 		unsigned long power_res = em_scale_power(table[i].power);
 
 		table[i].cost = div64_u64(fmax * power_res,
 					  table[i].frequency);
+		if (table[i].cost >= prev_cost) {
+			dev_dbg(dev, "EM: OPP:%lu is inefficient\n",
+				table[i].frequency);
+		} else {
+			prev_cost = table[i].cost;
+		}
 	}
 
 	pd->table = table;
-- 
2.26.2