cpufreq: Add stop CPU callback to cpufreq_driver interface

This callback allows the driver to do clean up before the CPU is
completely down and its state cannot be modified.  This is used
by the intel_pstate driver to reduce the requested P state prior to
the core going away.  This is required because the requested P state
of the offline core is used to select the package P state. This
effectively sets the floor package P state to the requested P state on
the offline core.
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
[rjw: Minor modifications]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/cpu-freq/cpu-drivers.txt

@@ -61,7 +61,13 @@ target_index		-	See below on the differences.
 
 And optionally
 
-cpufreq_driver.exit -		A pointer to a per-CPU cleanup function.
+cpufreq_driver.exit -		A pointer to a per-CPU cleanup
+				function called during CPU_POST_DEAD
+				phase of cpu hotplug process.
+
+cpufreq_driver.stop_cpu -	A pointer to a per-CPU stop function
+				called during CPU_DOWN_PREPARE phase of
+				cpu hotplug process.
 
 cpufreq_driver.resume -		A pointer to a per-CPU resume function
 				which is called with interrupts disabled

drivers/cpufreq/cpufreq.c

@@ -1337,6 +1337,8 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
 				pr_debug("%s: policy Kobject moved to cpu: %d from: %d\n",
 					 __func__, new_cpu, cpu);
 		}
+	} else if (cpufreq_driver->stop_cpu && cpufreq_driver->setpolicy) {
+		cpufreq_driver->stop_cpu(policy);
 	}
 
 	return 0;

include/linux/cpufreq.h

@@ -227,6 +227,7 @@ struct cpufreq_driver {
 	int	(*bios_limit)	(int cpu, unsigned int *limit);
 
 	int	(*exit)		(struct cpufreq_policy *policy);
+	void	(*stop_cpu)	(struct cpufreq_policy *policy);
 	int	(*suspend)	(struct cpufreq_policy *policy);
 	int	(*resume)	(struct cpufreq_policy *policy);
 	struct freq_attr	**attr;