cpufreq: Bring CPUs up even if cpufreq_online() failed

There is a report that after commit 27622b06 ("cpufreq: Convert
to hotplug state machine"), the normal CPU offline/online cycle
fails on some platforms.

According to the ftrace result, this problem was triggered on
platforms using acpi-cpufreq as the default cpufreq driver,
and due to the lack of some ACPI freq method (eg. _PCT),
cpufreq_online() failed and returned a negative value, so the CPU
hotplug state machine rolled back the CPU online process.  Actually,
from the user's perspective, the failure of cpufreq_online() should
not prevent that CPU from being brought up, although cpufreq might
not work on that CPU.

BTW, during system startup cpufreq_online() is not invoked via CPU
online but by the cpufreq device creation process, so the APs can be
brought up even though cpufreq_online() fails in that stage.

This patch ignores the return value of cpufreq_online/offline() and
lets the cpufreq framework deal with the failure.  cpufreq_online()
itself will do a proper rollback in that case and if _PCT is missing,
the ACPI cpufreq driver will print a warning if the corresponding
debug options have been enabled.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=194581
Fixes: 27622b06 ("cpufreq: Convert to hotplug state machine")
Reported-and-tested-by: Tomasz Maciej Nowak <tmn505@gmail.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: 4.9+ <stable@vger.kernel.org> # 4.9+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq.c

@@ -2398,6 +2398,20 @@ EXPORT_SYMBOL_GPL(cpufreq_boost_enabled);
  *********************************************************************/
 static enum cpuhp_state hp_online;
 
+static int cpuhp_cpufreq_online(unsigned int cpu)
+{
+	cpufreq_online(cpu);
+
+	return 0;
+}
+
+static int cpuhp_cpufreq_offline(unsigned int cpu)
+{
+	cpufreq_offline(cpu);
+
+	return 0;
+}
+
 /**
  * cpufreq_register_driver - register a CPU Frequency driver
  * @driver_data: A struct cpufreq_driver containing the values#
@@ -2460,8 +2474,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	}
 
 	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "cpufreq:online",
-					cpufreq_online,
-					cpufreq_offline);
+					cpuhp_cpufreq_online,
+					cpuhp_cpufreq_offline);
 	if (ret < 0)
 		goto err_if_unreg;
 	hp_online = ret;