From 12fdc5c1caed35b336f7fe2db2f4104d81626b71 Mon Sep 17 00:00:00 2001
From: Tim Gardner <tim.gardner@canonical.com>
Date: Tue, 24 Apr 2012 11:47:18 -0600
Subject: [PATCH] UBUNTU: SAUCE: (no-up) Allow filtering of cpufreq drivers

Harmless patch that allows k8 powernow machines to boot. Carry until
conflict.

BugLink: http://bugs.launchpad.net/bugs/984288

Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Herton Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
[ arighi: context adjustment (cpu0_hotplug has been removed) ]
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
---
 .../admin-guide/kernel-parameters.txt         |  4 ++++
 drivers/cpufreq/cpufreq.c                     | 22 ++++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 31b3a25680d0..a12fd038fe25 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -848,6 +848,10 @@
 			Format:
 			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 
+	cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
+			to register. Example: cpufreq_driver=powernow-k8
+			Format: { none | STRING }
+
 	cpuidle.off=1	[CPU_IDLE]
 			disable the cpuidle sub-system
 
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 44db4f59c4cc..cdd0f3527023 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2841,6 +2841,20 @@ static int cpuhp_cpufreq_offline(unsigned int cpu)
 	return 0;
 }
 
+static char cpufreq_driver_name[CPUFREQ_NAME_LEN];
+
+static int __init cpufreq_driver_setup(char *str)
+{
+	strlcpy(cpufreq_driver_name, str, CPUFREQ_NAME_LEN);
+	return 1;
+}
+
+/*
+ * Set this name to only allow one specific cpu freq driver, e.g.,
+ * cpufreq_driver=powernow-k8
+ */
+__setup("cpufreq_driver=", cpufreq_driver_setup);
+
 /**
  * cpufreq_register_driver - register a CPU Frequency driver
  * @driver_data: A struct cpufreq_driver containing the values#
@@ -2876,7 +2890,13 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 		 (driver_data->adjust_perf && !driver_data->fast_switch))
 		return -EINVAL;
 
-	pr_debug("trying to register driver %s\n", driver_data->name);
+	pr_debug("trying to register driver %s, cpufreq_driver=%s\n",
+		driver_data->name, cpufreq_driver_name);
+
+	if (cpufreq_driver_name[0])
+		if (!driver_data->name ||
+			strcmp(cpufreq_driver_name, driver_data->name))
+				return -EINVAL;
 
 	/* Protect against concurrent CPU online/offline. */
 	cpus_read_lock();