linux-kernel - Re: [RFC][PATCH 2/3] PM: Asynchronous suspend of devices

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Date:	Sat, 15 Aug 2009 23:04:59 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	"linux-pm" <linux-pm@...ts.linux-foundation.org>,
	"linux-acpi" <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>, Len Brown <lenb@...nel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [RFC][PATCH 2/3] PM: Asynchronous suspend of devices

On Friday 14 August 2009, Pavel Machek wrote:
> > @@ -659,26 +674,61 @@ static pm_message_t resume_event(pm_mess
> >  }
> >  
> >  /**
> > - *	device_suspend_noirq - Shut down one device (late suspend).
> > - *	@dev:	Device.
> > - *	@state: PM transition of the system being carried out.
> > + * __device_suspend_noirq - Execute a "late" suspend callback for given device.
> > + * @dev: Device to suspend.
> > + * @state: PM transition of the system being carried out.
> 
> >   *
> > - *	This is called with interrupts off and only a single CPU running.
> 
> that still looks like useful comment... why delete it?

Because it's not valid any more.

> > + * The driver of the device won't receive interrupts while this function is
> > + * being executed.
> >   */
> > @@ -696,13 +746,19 @@ int dpm_suspend_noirq(pm_message_t state
> >  	suspend_device_irqs();
> >  	mutex_lock(&dpm_list_mtx);
> >  	list_for_each_entry_reverse(dev, &dpm_list, power.entry) {
> > +		dev->power.status = DPM_OFF_IRQ;
> >  		error = device_suspend_noirq(dev, state);
> >  		if (error) {
> >  			pm_dev_err(dev, state, " late", error);
> > +			dev->power.status = DPM_OFF;
> > +			break;
> > +		}
> > +		if (async_error) {
> > +			error = async_error;
> >  			break;
> 
> async_error is 'interesting'. How does locking work in noirq case?

It's racy, a little bit. :-)

If two async drivers return errors exactly at the same time, one of them will
win the race, but it doesn't really matter which one wins as long as
async_error is different from zero as a result.  And it will be, since it's
an 'int' and the integrity of these is guaranteed.

Thanks,
Rafael
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