linux-kernel - [PATCH 2/2] cpufreq: arm_big_little: set 'physical

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Date:	Fri, 14 Mar 2014 12:10:55 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	rjw@...ysocki.net
Cc:	linaro-kernel@...ts.linaro.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	xin.wang@....com, arvind.chauhan@....com, Sudeep.Holla@....com,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH 2/2] cpufreq: arm_big_little: set 'physical_cluster' for each cpu

We have a per-cpu variable for managing which cluster does a CPU belong to.
Currently physical_cluster is set only for the policy->cpu. And that results in
following on some SoC's:

- There are two clusters:
  - Cluster 0 has four ARM Cortex A7 CPUs (slower ones): 0,1,2,3
  - Cluster 1 has four ARM Cortex A15 CPUs (faster ones): 4,5,6,7
- CPUs are booted in order 0,1..7 and so initially policy->cpu for A7 cluster
  would be 0 and for A15 cluster would be 4.
- Now CPU4 (i.e. A15_0) is hotplugged out and so policy->cpu for A15 cluster
  becomes 5 (i.e. A15_1).
- But physical cluster is only set for CPU0 and CPU4 in ARM big LITTLE driver
  and isn't updated.
- Now freq change request comes for A15 cluster and we would try to update freq
  of physical_cluster of CPU5, i.e. A15_1. And it is currently set to zero
  (default value of uninitialized global variables).
- And so we actually try to change freq of A7 cluster instead of A15.
- This also results in kernel crash as sometimes we might request freq above
  A7's limit and CPU may behave badly..

Fix this by initializing physical_cluster for all CPUs of a policy.

(Adding signed-off by Xin as he reported this issue and provided this diff)

Signed-off-by: Xin Wang <xin.wang@....com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/cpufreq/arm_big_little.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/arm_big_little.c b/drivers/cpufreq/arm_big_little.c
index 3d87078..bad2ed3 100644
--- a/drivers/cpufreq/arm_big_little.c
+++ b/drivers/cpufreq/arm_big_little.c
@@ -446,9 +446,12 @@ static int bL_cpufreq_init(struct cpufreq_policy *policy)
 	}
 
 	if (cur_cluster < MAX_CLUSTERS) {
+		int cpu;
+
 		cpumask_copy(policy->cpus, topology_core_cpumask(policy->cpu));
 
-		per_cpu(physical_cluster, policy->cpu) = cur_cluster;
+		for_each_cpu(cpu, policy->cpus)
+			per_cpu(physical_cluster, cpu) = cur_cluster;
 	} else {
 		/* Assumption: during init, we are always running on A15 */
 		per_cpu(physical_cluster, policy->cpu) = A15_CLUSTER;
-- 
1.7.12.rc2.18.g61b472e

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