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>