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    Subject[PATCH 4.10 48/69] cpufreq: Bring CPUs up even if cpufreq_online() failed
    Date
    4.10-stable review patch.  If anyone has any objections, please let me know.

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

    From: Chen Yu <yu.c.chen@intel.com>

    commit c4a3fa261b16858416f1fd7db03a33d7ef5fc0b3 upstream.

    There is a report that after commit 27622b061eb4 ("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: 27622b061eb4 ("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>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/cpufreq/cpufreq.c | 18 ++++++++++++++++--
    1 file changed, 16 insertions(+), 2 deletions(-)

    --- a/drivers/cpufreq/cpufreq.c
    +++ b/drivers/cpufreq/cpufreq.c
    @@ -2405,6 +2405,20 @@ 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#
    @@ -2467,8 +2481,8 @@ int cpufreq_register_driver(struct cpufr
    }

    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;

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