linux-kernel - Re: [RFC][PATCH 1/2] PM: Add support for device power domains

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Date:	Mon, 14 Feb 2011 11:12:48 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kevin Hilman <khilman@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Len Brown <lenb@...nel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC][PATCH 1/2] PM: Add support for device power domains

On Sat, 12 Feb 2011, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> The platform bus type is often used to handle Systems-on-a-Chip (SoC)
> where all devices are represented by objects of type struct
> platform_device.  In those cases the same "platform" device driver
> may be used with multiple different system configurations, but the
> actions needed to put the devices it handles into a low-power state
> and back into the full-power state may depend on the design of the
> given SoC.  The driver, however, cannot possibly include all the
> information necessary for the power management of its device on all
> the systems it is used with.  Moreover, the device hierarchy in its
> current form also is not suitable for representing this kind of
> information.
> 
> The patch below attempts to address this problem by introducing
> objects of type struct dev_power_domain that can be used for
> representing power domains within a SoC.  Every struct
> dev_power_domain object provides a sets of device power
> management callbacks that can be used to perform what's needed for
> device power management in addition to the operations carried out by
> the device's driver and subsystem.
> 
> Namely, if a struct dev_power_domain object is pointed to by the
> pwr_domain field in a struct device, the callbacks provided by its
> ops member will be executed in addition to the corresponding
> callbacks provided by the device's subsystem and driver during all
> power transitions.

Overall this looks very good.

> Index: linux-2.6/include/linux/pm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/pm.h
> +++ linux-2.6/include/linux/pm.h
> @@ -463,6 +463,14 @@ struct dev_pm_info {
>  
>  extern void update_pm_runtime_accounting(struct device *dev);
>  
> +/*
> + * Power domains provide callbacks that are executed during system suspend,
> + * hibernation, system resume and during runtime PM transitions along with
> + * subsystem-level and driver-level callbacks.
> + */
> +struct dev_power_domain {
> +	struct dev_pm_ops	ops;
> +};

I don't have a clear picture of how people are going to want to use 
these dev_power_domain structures.  Should there be a

	void			*priv;

member as well?

Alan Stern

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