linux-kernel - Re: [PATCH v5 1/2] PM / sleep: Go direct

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Date:	Tue, 29 Sep 2015 10:39:20 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
cc:	linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
	<martyn.welch@...labora.co.uk>, <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>,
	Kevin Hilman <khilman@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Pavel Machek <pavel@....cz>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v5 1/2] PM / sleep: Go direct_complete if driver has no
 callbacks

On Tue, 29 Sep 2015, Tomeu Vizoso wrote:

> If a suitable prepare callback cannot be found for a given device and
> its driver has no PM callbacks at all, assume that it can go direct to
> complete when the system goes to sleep.
> 
> The reason for this is that there's lots of devices in a system that do
> no PM at all and there's no reason for them to prevent their ancestors
> to do direct_complete if they can support it.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>

> +void device_check_pm_callbacks(struct device *dev)
> +{
> +	dev->power.no_pm_callbacks =
> +		(!dev->bus || pm_ops_is_empty(dev->bus->pm)) &&
> +		(!dev->class || pm_ops_is_empty(dev->class->pm)) &&
> +		(!dev->type || pm_ops_is_empty(dev->type->pm)) &&
> +		(!dev->pm_domain || pm_ops_is_empty(&dev->pm_domain->ops)) &&
> +		(!dev->driver || pm_ops_is_empty(dev->driver->pm));
> +}

One fairly minor point: You should lock dev->power.lock before setting
this bitfield.  This is because bitfields are not SMP-safe.

Alan Stern

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