linux-kernel - Re: [PATCH v2] PM / sleep: Let devices force direct

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Date:	Thu, 14 May 2015 14:12:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
cc:	linux-pm@...r.kernel.org,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Kevin Hilman <khilman@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PM / sleep: Let devices force direct_complete

On Thu, 14 May 2015, Tomeu Vizoso wrote:

> Introduce a new per-device flag power.force_direct_complete that will
> instruct the PM core to let that device remain in runtime suspend when
> the system goes into a sleep power state, regardless of the PM state of
> any of its descendants.
> 
> This is needed because otherwise it would be needed to get dozens of
> drivers to implement the prepare() callback and be runtime PM active
> even if they don't have a 1-to-1 relationship with a piece of HW.
> 
> This only applies to devices that aren't wakeup-capable, as those would
> need to setup their IRQs as wakeup-capable in their prepare() callbacks.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>

There's one little problem in this...

> @@ -1605,9 +1607,13 @@ static int device_prepare(struct device *dev, pm_message_t state)
>  	 * will do the same thing with all of its descendants".  This only
>  	 * applies to suspend transitions, however.
>  	 */
> -	spin_lock_irq(&dev->power.lock);
> -	dev->power.direct_complete = ret > 0 && state.event == PM_EVENT_SUSPEND;
> -	spin_unlock_irq(&dev->power.lock);
> +	if (state.event == PM_EVENT_SUSPEND) {
> +		spin_lock_irq(&dev->power.lock);
> +		dev->power.direct_complete = ret > 0 ||
> +			(dev->power.force_direct_complete &&
> +			 !device_can_wakeup(dev));
> +		spin_unlock_irq(&dev->power.lock);
> +	}

When state.event is not PM_EVENT_SUSPEND, this fails to set 
dev->power.direct_complete to 0.  Sticking closer to the original code 
arrangement would help.

Aside from that small issue:

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern


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