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SubjectRe: [RFC][PATCH 1/3] PM: Asynchronous resume of devices
Date
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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