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    Subject[PATCH v2] drivers: base: add support to skip power management in device/driver model
    Date
    All device objects in the driver model contain fields that control the
    handling of various power management activities. However, it's not
    always useful. There are few instances where pseudo devices are added
    to the model just to take advantage of many other features like
    kobjects, udev events, and so on. One such example is cpu devices and
    their caches.

    The sysfs for the cpu caches are managed by adding devices with cpu
    as the parent in cpu_device_create() when secondary cpu is brought
    online. Generally when the secondary CPUs are hotplugged back in as part
    of resume from suspend-to-ram, we call cpu_device_create() from the cpu
    hotplug state machine while the cpu device associated with that CPU is
    not yet ready to be resumed as the device_resume() call happens bit
    later. It's not really needed to set the flag is_prepared for cpu
    devices as they are mostly pseudo device and hotplug framework deals
    with state machine and not managed through the cpu device.

    This often results in annoying warning when resuming:
    Enabling non-boot CPUs ...
    CPU1: Booted secondary processor
    cache: parent cpu1 should not be sleeping
    CPU1 is up
    CPU2: Booted secondary processor
    cache: parent cpu2 should not be sleeping
    CPU2 is up
    .... and so on.

    So in order to fix these kind of errors, we could just completely avoid
    doing any power management related initialisations and operations if
    they are not used by these devices.

    Lets add no_pm_required flags to indicate that the device doesn't
    require any sort of pm activities and all of them can be completely
    skipped. We can use the same flag to also avoid adding not used *power*
    sysfs entries for these devices. For now, lets use this for cpu cache
    devices.

    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: "Rafael J. Wysocki" <rafael@kernel.org>
    Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
    ---
    drivers/base/cpu.c | 1 +
    drivers/base/power/main.c | 7 +++++++
    drivers/base/power/sysfs.c | 4 ++++
    include/linux/device.h | 10 ++++++++++
    include/linux/pm.h | 1 +
    5 files changed, 23 insertions(+)

    v1->v2:
    - dropped setting the flag for cpu devices, for now just cpu caches
    will make use of this new flag.

    RFC->v1:
    - dropped the idea of adding cpu hotplug callback to deal just
    with cpu devices, instead add a new flag in the device pm_info
    structure

    [RFC] : https://marc.info/?l=linux-pm&m=154842896407904&w=2
    [v1] : https://marc.info/?l=linux-pm&m=154946578717730&w=2

    diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
    index eb9443d5bae1..6ce93a52bf3f 100644
    --- a/drivers/base/cpu.c
    +++ b/drivers/base/cpu.c
    @@ -427,6 +427,7 @@ __cpu_device_create(struct device *parent, void *drvdata,
    dev->parent = parent;
    dev->groups = groups;
    dev->release = device_create_release;
    + device_set_pm_not_required(dev);
    dev_set_drvdata(dev, drvdata);

    retval = kobject_set_name_vargs(&dev->kobj, fmt, args);
    diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
    index 0992e67e862b..2a29c3d4e240 100644
    --- a/drivers/base/power/main.c
    +++ b/drivers/base/power/main.c
    @@ -124,6 +124,10 @@ void device_pm_unlock(void)
    */
    void device_pm_add(struct device *dev)
    {
    + /* No need to create pm sysfs if explicitly specified as not required */
    + if (device_pm_not_required(dev))
    + return;
    +
    pr_debug("PM: Adding info for %s:%s\n",
    dev->bus ? dev->bus->name : "No Bus", dev_name(dev));
    device_pm_check_callbacks(dev);
    @@ -142,6 +146,9 @@ void device_pm_add(struct device *dev)
    */
    void device_pm_remove(struct device *dev)
    {
    + if (device_pm_not_required(dev))
    + return;
    +
    pr_debug("PM: Removing info for %s:%s\n",
    dev->bus ? dev->bus->name : "No Bus", dev_name(dev));
    complete_all(&dev->power.completion);
    diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
    index d713738ce796..6cd159b51114 100644
    --- a/drivers/base/power/sysfs.c
    +++ b/drivers/base/power/sysfs.c
    @@ -648,6 +648,10 @@ int dpm_sysfs_add(struct device *dev)
    {
    int rc;

    + /* No need to create pm sysfs if explicitly disabled */
    + if (device_pm_not_required(dev))
    + return 0;
    +
    rc = sysfs_create_group(&dev->kobj, &pm_attr_group);
    if (rc)
    return rc;
    diff --git a/include/linux/device.h b/include/linux/device.h
    index 6cb4640b6160..739d0b62e4d4 100644
    --- a/include/linux/device.h
    +++ b/include/linux/device.h
    @@ -1165,6 +1165,16 @@ static inline bool device_async_suspend_enabled(struct device *dev)
    return !!dev->power.async_suspend;
    }

    +static inline bool device_pm_not_required(struct device *dev)
    +{
    + return dev->power.no_pm_required;
    +}
    +
    +static inline void device_set_pm_not_required(struct device *dev)
    +{
    + dev->power.no_pm_required = true;
    +}
    +
    static inline void dev_pm_syscore_device(struct device *dev, bool val)
    {
    #ifdef CONFIG_PM_SLEEP
    diff --git a/include/linux/pm.h b/include/linux/pm.h
    index 0bd9de116826..300ab9f0b858 100644
    --- a/include/linux/pm.h
    +++ b/include/linux/pm.h
    @@ -592,6 +592,7 @@ struct dev_pm_info {
    bool is_suspended:1; /* Ditto */
    bool is_noirq_suspended:1;
    bool is_late_suspended:1;
    + bool no_pm_required:1;
    bool early_init:1; /* Owned by the PM core */
    bool direct_complete:1; /* Owned by the PM core */
    u32 driver_flags;
    --
    2.17.1
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