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

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Message-Id: <200908222346.49736.rjw@sisk.pl>
Date:	Sat, 22 Aug 2009 23:46:49 +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 Saturday 22 August 2009, Pavel Machek wrote:
> > > > + * 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.
> 
> Rather than relying on atomicity of 'int' (where half of kernel
> hackers says it is and second half says it is not), can we just use
> atomic_t? It compiles to same code on sane architectures, and serves
> as documentation/warning...

I used atomic_t for that in the updated patches, already sent a few days ago.
Please refer to that code.

Thanks,
Rafael
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