Re: [PATCH v5 1/2] PM / sleep: Go direct_complete if driver has no callbacks

[Tomeu Vizoso]

On 4 October 2015 at 17:16, Pavel Machek <pavel@xxxxxx> wrote:
> On Tue 2015-09-29 14:29:19, Tomeu Vizoso wrote:
>> If a suitable prepare callback cannot be found for a given device and
>> its driver has no PM callbacks at all, assume that it can go direct to
>> complete when the system goes to sleep.
>>
>> The reason for this is that there's lots of devices in a system that do
>> no PM at all and there's no reason for them to prevent their ancestors
>> to do direct_complete if they can support it.
>
> Dunno. This sounds like asking for trouble. Even if most devices can handle
> this, is not this bound to introduce some bugs?

Hi Pavel,

in which situations do you think that this could be problematic?

Thanks,

Tomeu

> Thanks,
>                                                                         Pavel
>
>>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
>> ---
>>
>> Changes in v5:
>> - Check for all dev_pm_ops instances associated to a device, updating a
>>   no_pm_callbacks flag at the times when that could change.
>>
>>  drivers/base/dd.c           |  3 ++
>>  drivers/base/power/domain.c |  5 ++++
>>  drivers/base/power/main.c   | 69 ++++++++++++++++++++++++++++++++-------------
>>  drivers/base/power/power.h  |  2 ++
>>  include/linux/pm.h          |  1 +
>>  5 files changed, 61 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index be0eb4639128..fe0e9cb684b8 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -205,6 +205,8 @@ static void driver_bound(struct device *dev)
>>
>>       klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
>>
>> +     device_check_pm_callbacks(dev);
>> +
>>       /*
>>        * Make sure the device is no longer in one of the deferred lists and
>>        * kick off retrying all pending devices
>> @@ -695,6 +697,7 @@ static void __device_release_driver(struct device *dev)
>>                       dev->pm_domain->dismiss(dev);
>>
>>               klist_remove(&dev->p->knode_driver);
>> +             device_check_pm_callbacks(dev);
>>               if (dev->bus)
>>                       blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
>>                                                    BUS_NOTIFY_UNBOUND_DRIVER,
>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>> index 16550c63d611..3cae1aa1885b 100644
>> --- a/drivers/base/power/domain.c
>> +++ b/drivers/base/power/domain.c
>> @@ -20,6 +20,8 @@
>>  #include <linux/suspend.h>
>>  #include <linux/export.h>
>>
>> +#include "power.h"
>> +
>>  #define GENPD_RETRY_MAX_MS   250             /* Approximate */
>>
>>  #define GENPD_DEV_CALLBACK(genpd, type, callback, dev)               \
>> @@ -1305,6 +1307,7 @@ int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
>>
>>       list_add_tail(&gpd_data->base.list_node, &genpd->dev_list);
>>
>> +     device_check_pm_callbacks(dev);
>>   out:
>>       mutex_unlock(&genpd->lock);
>>
>> @@ -1369,6 +1372,8 @@ int pm_genpd_remove_device(struct generic_pm_domain *genpd,
>>
>>       genpd_free_dev_data(dev, gpd_data);
>>
>> +     device_check_pm_callbacks(dev);
>> +
>>       return 0;
>>
>>   out:
>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>> index 1710c26ba097..b6eaa00b2540 100644
>> --- a/drivers/base/power/main.c
>> +++ b/drivers/base/power/main.c
>> @@ -117,6 +117,31 @@ void device_pm_unlock(void)
>>       mutex_unlock(&dpm_list_mtx);
>>  }
>>
>> +static bool pm_ops_is_empty(const struct dev_pm_ops *ops)
>> +{
>> +     if (!ops)
>> +             return true;
>> +
>> +     return !ops->prepare &&
>> +            !ops->suspend &&
>> +            !ops->suspend_late &&
>> +            !ops->suspend_noirq &&
>> +            !ops->resume_noirq &&
>> +            !ops->resume_early &&
>> +            !ops->resume &&
>> +            !ops->complete;
>> +}
>> +
>> +void device_check_pm_callbacks(struct device *dev)
>> +{
>> +     dev->power.no_pm_callbacks =
>> +             (!dev->bus || pm_ops_is_empty(dev->bus->pm)) &&
>> +             (!dev->class || pm_ops_is_empty(dev->class->pm)) &&
>> +             (!dev->type || pm_ops_is_empty(dev->type->pm)) &&
>> +             (!dev->pm_domain || pm_ops_is_empty(&dev->pm_domain->ops)) &&
>> +             (!dev->driver || pm_ops_is_empty(dev->driver->pm));
>> +}
>> +
>>  /**
>>   * device_pm_add - Add a device to the PM core's list of active devices.
>>   * @dev: Device to add to the list.
>> @@ -131,6 +156,8 @@ void device_pm_add(struct device *dev)
>>                       dev_name(dev->parent));
>>       list_add_tail(&dev->power.entry, &dpm_list);
>>       mutex_unlock(&dpm_list_mtx);
>> +
>> +     device_check_pm_callbacks(dev);
>>  }
>>
>>  /**
>> @@ -1569,27 +1596,31 @@ static int device_prepare(struct device *dev, pm_message_t state)
>>
>>       dev->power.wakeup_path = device_may_wakeup(dev);
>>
>> -     if (dev->pm_domain) {
>> -             info = "preparing power domain ";
>> -             callback = dev->pm_domain->ops.prepare;
>> -     } else if (dev->type && dev->type->pm) {
>> -             info = "preparing type ";
>> -             callback = dev->type->pm->prepare;
>> -     } else if (dev->class && dev->class->pm) {
>> -             info = "preparing class ";
>> -             callback = dev->class->pm->prepare;
>> -     } else if (dev->bus && dev->bus->pm) {
>> -             info = "preparing bus ";
>> -             callback = dev->bus->pm->prepare;
>> -     }
>> +     if (dev->power.no_pm_callbacks)
>> +             ret = 1;        /* Let device go direct_complete */
>> +     else {
>> +             if (dev->pm_domain) {
>> +                     info = "preparing power domain ";
>> +                     callback = dev->pm_domain->ops.prepare;
>> +             } else if (dev->type && dev->type->pm) {
>> +                     info = "preparing type ";
>> +                     callback = dev->type->pm->prepare;
>> +             } else if (dev->class && dev->class->pm) {
>> +                     info = "preparing class ";
>> +                     callback = dev->class->pm->prepare;
>> +             } else if (dev->bus && dev->bus->pm) {
>> +                     info = "preparing bus ";
>> +                     callback = dev->bus->pm->prepare;
>> +             }
>>
>> -     if (!callback && dev->driver && dev->driver->pm) {
>> -             info = "preparing driver ";
>> -             callback = dev->driver->pm->prepare;
>> -     }
>> +             if (!callback && dev->driver && dev->driver->pm) {
>> +                     info = "preparing driver ";
>> +                     callback = dev->driver->pm->prepare;
>> +             }
>>
>> -     if (callback)
>> -             ret = callback(dev);
>> +             if (callback)
>> +                     ret = callback(dev);
>> +     }
>>
>>       device_unlock(dev);
>>
>> diff --git a/drivers/base/power/power.h b/drivers/base/power/power.h
>> index 998fa6b23084..518a8fc84e8d 100644
>> --- a/drivers/base/power/power.h
>> +++ b/drivers/base/power/power.h
>> @@ -9,6 +9,8 @@ static inline void device_pm_init_common(struct device *dev)
>>       }
>>  }
>>
>> +extern void device_check_pm_callbacks(struct device *dev);
>> +
>>  #ifdef CONFIG_PM
>>
>>  static inline void pm_runtime_early_init(struct device *dev)
>> diff --git a/include/linux/pm.h b/include/linux/pm.h
>> index 35d599e7250d..e334b9b8cd46 100644
>> --- a/include/linux/pm.h
>> +++ b/include/linux/pm.h
>> @@ -566,6 +566,7 @@ struct dev_pm_info {
>>       bool                    ignore_children:1;
>>       bool                    early_init:1;   /* Owned by the PM core */
>>       bool                    direct_complete:1;      /* Owned by the PM core */
>> +     bool                    no_pm_callbacks:1;      /* Owned by the PM core */
>>       spinlock_t              lock;
>>  #ifdef CONFIG_PM_SLEEP
>>       struct list_head        entry;
>> --
>> 2.4.3
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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