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    SubjectRe: [RFC][PATCH 1/3] PM: Asynchronous resume of devices
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    On Friday 14 August 2009, Pavel Machek wrote:
    > > The patch below introduces a mechanism allowing some devices to be
    > > resumed asynchronously, using completions with the following rules:
    > > (1) There is a completion, dev->power.comp, for each device object.
    > > (2) All of these completions are reset before suspend as well as
    > > each resume stage (dpm_resume_noirq(), dpm_resume()).
    > > (3) If dev->power.async_suspend is set for dev or for its parent, the
    > > PM core waits for the parent's completion before attempting to
    > > run the resume callbacks, appropriate for this particular stage
    > > of resume, for dev.
    >
    > at least this needs to go in as a comment.

    OK, this is a prototype patch, still under discussion.

    > > (4) dev->power.comp is completed for each device after running its
    > > @@ -411,9 +412,12 @@ struct dev_pm_info {
    > > pm_message_t power_state;
    > > unsigned int can_wakeup:1;
    > > unsigned int should_wakeup:1;
    > > + unsigned async_suspend:1;
    > > enum dpm_state status; /* Owned by the PM core */
    >
    > unsigned int? Or bool?

    unsigned means 'unsigned int'. I should have added 'int', but again, this is
    a prototype patch.

    > Should it go under config_pm_sleep?

    Not necessaily. 'status' is not there as well.

    > > #ifdef CONFIG_PM_SLEEP
    > > struct list_head entry;
    > > + struct completion comp;
    > > + pm_message_t async_state;
    > > #endif
    > > }
    > >
    > > +static inline void device_enable_async_suspend(struct device *dev, bool enable)
    > > +{
    > > + if (dev->power.status == DPM_ON)
    > > + dev->power.async_suspend = enable;
    > > +}
    > > +
    > > @@ -163,6 +166,34 @@ void device_pm_move_last(struct device *
    > > list_move_tail(&dev->power.entry, &dpm_list);
    > > }
    > >
    > > +static void dpm_synchronize_noirq(void)
    > > +{
    > > + struct device *dev;
    > > +
    > > + async_synchronize_full();
    > > +
    > > + list_for_each_entry(dev, &dpm_list, power.entry)
    > > + INIT_COMPLETION(dev->power.comp);
    > > +}
    > > +
    > > +static void dpm_synchronize(void)
    > > +{
    > > + struct device *dev;
    > > +
    > > + async_synchronize_full();
    > > +
    > > + mutex_lock(&dpm_list_mtx);
    > > + list_for_each_entry(dev, &dpm_list, power.entry)
    > > + INIT_COMPLETION(dev->power.comp);
    > > + mutex_unlock(&dpm_list_mtx);
    > > +}
    >
    > Why is it ok to avoid locking in noirq case?

    It's not, but we hold dpm_list_mtx throughout the entire noirq suspend.

    > Do we really need async for noirq handlers?

    Yes, we do. Specifically, for PCI.

    > > /**
    > > - * device_resume_noirq - Power on one device (early resume).
    > > - * @dev: Device.
    > > - * @state: PM transition of the system being carried out.
    > > + * __device_resume_noirq - Execute an "early resume" callback for given device.
    > > + * @dev: Device to resume.
    > > + * @state: PM transition of the system being carried out.
    > > *
    > > - * Must be called with interrupts disabled.
    > > + * The driver of the device won't receive interrupts while this function is
    > > + * being executed.
    > > */
    >
    > You still want it called with interrupts disabled, right?

    No. It's not called with interrupts off now.

    Thanks,
    Rafael


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