linux-kernel - [PATCH 4.2.y-ckt 159/211] cpufreq: arm_big_little: fix frequency check when bL switcher is active

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Date:	Tue,  5 Jan 2016 11:44:27 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jon Medhurst <tixy@...aro.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 159/211] cpufreq: arm_big_little: fix frequency check when bL switcher is active

4.2.8-ckt1 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Jon Medhurst \\(Tixy\\)" <tixy@...aro.org>

commit 14f1ba3af6209f0394192ef07fe2bd9bccdc755f upstream.

The check for correct frequency being set in bL_cpufreq_set_rate is
broken when the big.LITTLE switcher is active, for two reasons.

 1. The 'new_rate' variable gets overwritten before the test by the
 code calculating the frequency of the old cluster.

 2. The frequency returned by bL_cpufreq_get_rate will be the virtual
 frequency, not the actual one the intended version of new_rate contains.

This means the function always returns an error causing an endless
stream of: "cpufreq: __target_index: Failed to change cpu frequency: -5"

As the intent is to check for errors that clk_set_rate doesn't report
lets move the check to immediately after that and directly use
clk_get_rate, rather than the arm_big_little helpers which only confuse
matters. Also, update the comment to be hopefully clearer about the
purpose of the code.

Fixes: 0a95e630b49a (cpufreq: arm_big_little: check if the frequency is set correctly)
Signed-off-by: Jon Medhurst <tixy@...aro.org>
Acked-by: Sudeep Holla <sudeep.holla@....com>
Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
Reviewed-by: Michael Turquette <mturquette@...libre.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/cpufreq/arm_big_little.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/cpufreq/arm_big_little.c b/drivers/cpufreq/arm_big_little.c
index f1e42f8..c5d256c 100644
--- a/drivers/cpufreq/arm_big_little.c
+++ b/drivers/cpufreq/arm_big_little.c
@@ -149,6 +149,19 @@ bL_cpufreq_set_rate(u32 cpu, u32 old_cluster, u32 new_cluster, u32 rate)
 			__func__, cpu, old_cluster, new_cluster, new_rate);
 
 	ret = clk_set_rate(clk[new_cluster], new_rate * 1000);
+	if (!ret) {
+		/*
+		 * FIXME: clk_set_rate hasn't returned an error here however it
+		 * may be that clk_change_rate failed due to hardware or
+		 * firmware issues and wasn't able to report that due to the
+		 * current design of the clk core layer. To work around this
+		 * problem we will read back the clock rate and check it is
+		 * correct. This needs to be removed once clk core is fixed.
+		 */
+		if (clk_get_rate(clk[new_cluster]) != new_rate * 1000)
+			ret = -EIO;
+	}
+
 	if (WARN_ON(ret)) {
 		pr_err("clk_set_rate failed: %d, new cluster: %d\n", ret,
 				new_cluster);
@@ -189,15 +202,6 @@ bL_cpufreq_set_rate(u32 cpu, u32 old_cluster, u32 new_cluster, u32 rate)
 		mutex_unlock(&cluster_lock[old_cluster]);
 	}
 
-	/*
-	 * FIXME: clk_set_rate has to handle the case where clk_change_rate
-	 * can fail due to hardware or firmware issues. Until the clk core
-	 * layer is fixed, we can check here. In most of the cases we will
-	 * be reading only the cached value anyway. This needs to  be removed
-	 * once clk core is fixed.
-	 */
-	if (bL_cpufreq_get_rate(cpu) != new_rate)
-		return -EIO;
 	return 0;
 }
 
-- 
1.9.1

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