linux-kernel - [PATCH] cpufreq: Use a smaller freq for the policy->max when verify

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Date: Tue, 19 Mar 2024 16:01:53 +0800
From: Xuewen Yan <xuewen.yan@...soc.com>
To: <rafael@...nel.org>, <viresh.kumar@...aro.org>
CC: <ke.wang@...soc.com>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <xuewen.yan94@...il.com>,
        <di.shen@...soc.com>
Subject: [PATCH] cpufreq: Use a smaller freq for the policy->max when verify

When driver use the cpufreq_frequency_table_verify() as the
cpufreq_driver->verify's callback. It may cause the policy->max
bigger than the freq_qos's max freq.

Just as follow:

unisoc:/sys/devices/system/cpu/cpufreq/policy0 # cat scaling_available_frequencies
614400 768000 988000 1228800 1469000 1586000 1690000 1833000 2002000 2093000

unisoc:/sys/devices/system/cpu/cpufreq/policy0 # echo 1900000 > scaling_max_freq
unisoc:/sys/devices/system/cpu/cpufreq/policy0 # echo 1900000 > scaling_min_freq
unisoc:/sys/devices/system/cpu/cpufreq/policy0 # cat scaling_max_freq
2002000
unisoc:/sys/devices/system/cpu/cpufreq/policy0 # cat scaling_min_freq
2002000

When user set the qos_min and qos_max as the same value, and the value
is not in the freq-table, the above scenario will occur.

This is because in cpufreq_frequency_table_verify() func, when it can not
find the freq in table, it will change the policy->max to be a bigger freq,
as above, because there is no 1.9G in the freq-table, the policy->max would
be set to 2.002G. As a result, the cpufreq_policy->max is bigger than the
user's qos_max. This is unreasonable.

So use a smaller freq when can not find the freq in fre-table, to prevent
the policy->max exceed the qos's max freq.

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
---
 drivers/cpufreq/freq_table.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
index c4d4643b6ca6..1d98b8cf1688 100644
--- a/drivers/cpufreq/freq_table.c
+++ b/drivers/cpufreq/freq_table.c
@@ -70,7 +70,7 @@ int cpufreq_frequency_table_verify(struct cpufreq_policy_data *policy,
 				   struct cpufreq_frequency_table *table)
 {
 	struct cpufreq_frequency_table *pos;
-	unsigned int freq, next_larger = ~0;
+	unsigned int freq, prev_smaller = 0;
 	bool found = false;
 
 	pr_debug("request for verification of policy (%u - %u kHz) for cpu %u\n",
@@ -86,12 +86,12 @@ int cpufreq_frequency_table_verify(struct cpufreq_policy_data *policy,
 			break;
 		}
 
-		if ((next_larger > freq) && (freq > policy->max))
-			next_larger = freq;
+		if ((prev_smaller < freq) && (freq <= policy->max))
+			prev_smaller = freq;
 	}
 
 	if (!found) {
-		policy->max = next_larger;
+		policy->max = prev_smaller;
 		cpufreq_verify_within_cpu_limits(policy);
 	}
 
-- 
2.25.1