linux-kernel - [PATCH] cpufreq: Make sure CPU is running on a freq from freq-table

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Date:	Thu, 21 Nov 2013 12:39:02 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	rjw@...ysocki.net, nm@...com
Cc:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, shawn.guo@...aro.org, ceh@...com,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH] cpufreq: Make sure CPU is running on a freq from freq-table

Sometimes boot loaders set CPU frequency to a value outside of frequency table
present with cpufreq core. In such cases CPU might be unstable if it has to run
on that frequency for long duration of time and so its better to set it to a
frequency which is specified in freq-table. This also makes cpufreq stats
inconsistent as cpufreq-stats would fail to register because current frequency
of CPU isn't found in freq-table.

Because we don't want this change to effect boot process badly, we go for the
next freq which is >= policy->cur ('cur' must be set by now, otherwise we will
end up setting freq to lowest of the table as 'cur' is initialized to zero).

In case where CPU is already running on one of the frequencies present in
freq-table, this would turn into a dummy call as __cpufreq_driver_target() would
return early.

Reported-by: Carlos Hernandez <ceh@...com>
Reported-by: Nishanth Menon <nm@...com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
After lots of discussion with Nishanth and others, I feel something like this..

@Nishanth: Please see if this works for you and I hope we don't need any of
these patches anymore:

- https://lkml.org/lkml/2013/11/15/569 : cpufreq: cpufreq-cpu0: Use a sane boot
frequency when booting with a mismatched bootloader configuration
- https://lkml.org/lkml/2013/11/15/503 : cpufreq: stats: Do not populate stats
  when policy->cur has no exact match
- https://lkml.org/lkml/2013/11/19/16 : cpufreq/stats: Add "unknown" frequency
  field in stats tables

 drivers/cpufreq/cpufreq.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 02d534d..d55c843 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1038,6 +1038,32 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
 		}
 	}
 
+	/*
+	 * Sometimes boot loaders set CPU frequency to a value outside of
+	 * frequency table present with cpufreq core. In such cases CPU might be
+	 * unstable if it has to run on that frequency for long duration of time
+	 * and so its better to set it to a frequency which is specified in
+	 * freq-table. This also makes cpufreq stats inconsistent as
+	 * cpufreq-stats would fail to register because current frequency of CPU
+	 * isn't found in freq-table.
+	 *
+	 * Because we don't want this change to effect boot process badly, we go
+	 * for the next freq which is >= policy->cur ('cur' must be set by now,
+	 * otherwise we will end up setting freq to lowest of the table as 'cur'
+	 * is initialized to zero).
+	 *
+	 * In case where CPU is already running on one of the frequencies
+	 * present in freq-table, this would turn into a dummy call as
+	 * __cpufreq_driver_target() would return early.
+	 */
+	if (has_target()) {
+		ret = __cpufreq_driver_target(policy, policy->cur,
+				CPUFREQ_RELATION_L);
+		if (ret)
+			pr_err("%s: Unable to set frequency from table: %d\n",
+					__func__, ret);
+	}
+
 	/* related cpus should atleast have policy->cpus */
 	cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
 
-- 
1.7.12.rc2.18.g61b472e

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