[3.16.y-ckt stable] Patch "cpufreq: Schedule work for the first-online CPU on resume" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    cpufreq: Schedule work for the first-online CPU on resume

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e5fa3f26f924e55cb54d96714d41c5ffd55b5ace Mon Sep 17 00:00:00 2001
From: Viresh Kumar <viresh.kumar at linaro.org>
Date: Thu, 2 Apr 2015 10:21:33 +0530
Subject: cpufreq: Schedule work for the first-online CPU on resume

commit c75de0ac0756d4b442f460e10461720c7c2412c2 upstream.

All CPUs leaving the first-online CPU are hotplugged out on suspend and
and cpufreq core stops managing them.

On resume, we need to call cpufreq_update_policy() for this CPU's policy
to make sure its frequency is in sync with cpufreq's cached value, as it
might have got updated by hardware during suspend/resume.

The policies are always added to the top of the policy-list. So, in
normal circumstances, CPU 0's policy will be the last one in the list.
And so the code checks for the last policy.

But there are cases where it will fail. Consider quad-core system, with
policy-per core. If CPU0 is hotplugged out and added back again, the
last policy will be on CPU1 :(

To fix this in a proper way, always look for the policy of the first
online CPU. That way we will be sure that we are calling
cpufreq_update_policy() for the only CPU that wasn't hotplugged out.

Fixes: 2f0aea936360 ("cpufreq: suspend governors on system suspend/hibernate")
Reported-by: Saravana Kannan <skannan at codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar at linaro.org>
Acked-by: Saravana Kannan <skannan at codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/cpufreq/cpufreq.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index f1c5e49ece97..8afa0a96f9dd 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1725,15 +1725,18 @@ void cpufreq_resume(void)
 		    || __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS))
 			pr_err("%s: Failed to start governor for policy: %p\n",
 				__func__, policy);
-
-		/*
-		 * schedule call cpufreq_update_policy() for boot CPU, i.e. last
-		 * policy in list. It will verify that the current freq is in
-		 * sync with what we believe it to be.
-		 */
-		if (list_is_last(&policy->policy_list, &cpufreq_policy_list))
-			schedule_work(&policy->update);
 	}
+
+	/*
+	 * schedule call cpufreq_update_policy() for first-online CPU, as that
+	 * wouldn't be hotplugged-out on suspend. It will verify that the
+	 * current freq is in sync with what we believe it to be.
+	 */
+	policy = cpufreq_cpu_get_raw(cpumask_first(cpu_online_mask));
+	if (WARN_ON(!policy))
+		return;
+
+	schedule_work(&policy->update);
 }

 /**