cpufreq: Avoid unnecessary frequency updates due to mismatch

[ Upstream commit ddb8abb596023105a56d8f834d11461e8266c164 ]

For some platforms, the frequency returned by hardware may be slightly
different from what is provided in the frequency table. For example,
hardware may return 499 MHz instead of 500 MHz. In such cases it is
better to avoid getting into unnecessary frequency updates, as we may
end up switching policy->cur between the two and sending unnecessary
pre/post update notifications, etc.

This patch has chosen allows the hardware frequency and table frequency
to deviate by 1 MHz for now, we may want to increase it a bit later on
if someone still complains.

Reported-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Jia-wei Chang <jia-wei.chang@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index eeac6d809229849d1b293fdc1984ba6694fefb68..cddf7e13c232210e0348d1467005a06bd1a2eb04 100644 (file)
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -28,6 +28,7 @@
 #include <linux/suspend.h>
 #include <linux/syscore_ops.h>
 #include <linux/tick.h>
+#include <linux/units.h>
 #include <trace/events/power.h>
 
 static LIST_HEAD(cpufreq_policy_list);
@@ -1701,6 +1702,16 @@ static unsigned int cpufreq_verify_current_freq(struct cpufreq_policy *policy, b
                return new_freq;
 
        if (policy->cur != new_freq) {
+               /*
+                * For some platforms, the frequency returned by hardware may be
+                * slightly different from what is provided in the frequency
+                * table, for example hardware may return 499 MHz instead of 500
+                * MHz. In such cases it is better to avoid getting into
+                * unnecessary frequency updates.
+                */
+               if (abs(policy->cur - new_freq) < HZ_PER_MHZ)
+                       return policy->cur;
+
                cpufreq_out_of_sync(policy, new_freq);
                if (update)
                        schedule_work(&policy->update);