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    Subject[PATCH 2/4] cpu: expose pm_qos_resume_latency for each cpu
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    The cpu-dma PM QoS constraint impacts all the cpus in the system. There
    is no way to let the user to choose a PM QoS constraint per cpu.

    The following patch exposes to the userspace a per cpu based sysfs file
    in order to let the userspace to change the value of the PM QoS latency
    constraint.

    This change is inoperative in its form and the cpuidle governors have to
    take into account the per cpu latency constraint in addition to the
    global cpu-dma latency constraint in order to operate properly.

    BTW
    The pm_qos_resume_latency usage defined in
    Documentation/ABI/testing/sysfs-devices-power
    The /sys/devices/.../power/pm_qos_resume_latency_us attribute
    contains the PM QoS resume latency limit for the given device,
    which is the maximum allowed time it can take to resume the
    device, after it has been suspended at run time, from a resume
    request to the moment the device will be ready to process I/O,
    in microseconds. If it is equal to 0, however, this means that
    the PM QoS resume latency may be arbitrary.

    Signed-off-by: Alex Shi <alex.shi@linaro.org>
    To: linux-kernel@vger.kernel.org
    To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: linux-pm@vger.kernel.org
    Cc: Ulf Hansson <ulf.hansson@linaro.org>
    Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
    ---
    drivers/base/cpu.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
    index 4c28e1a..ba11e23 100644
    --- a/drivers/base/cpu.c
    +++ b/drivers/base/cpu.c
    @@ -17,6 +17,7 @@
    #include <linux/of.h>
    #include <linux/cpufeature.h>
    #include <linux/tick.h>
    +#include <linux/pm_qos.h>

    #include "base.h"

    @@ -376,6 +377,8 @@ int register_cpu(struct cpu *cpu, int num)

    per_cpu(cpu_sys_devices, num) = &cpu->dev;
    register_cpu_under_node(num, cpu_to_node(num));
    + if (dev_pm_qos_expose_latency_limit(&cpu->dev, 0))
    + pr_debug("CPU%d: add resume latency failed\n", num);

    return 0;
    }
    --
    2.8.1.101.g72d917a
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