linux-kernel - Re: [PATCH 5] PM: Update comments describing device power management callbacks

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Date:	Tue, 22 Nov 2011 16:02:49 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Randy Dunlap <rdunlap@...otime.net>
Subject: Re: [PATCH 5] PM: Update comments describing device power management
 callbacks

On Tue, 22 Nov 2011, Rafael J. Wysocki wrote:

> > The same data structure (dev_pm_ops) is used for both drivers and
> > subsystems.  Therefore the comments should be directed toward both
> > driver writers and subsystem writers.
> 
> I don't quite agree.  Trying to do so would turn that comment into a lengthy
> document and there's no room for anything like that in the header file.

That's a good point.

> Perhaps I'll just modify the comment to say when the callbacks are executed
> without specifying what the specific callbacks are supposed to do (because
> that may vary from one subsystem to another and even between different
> drivers belonging to the same subsystem).  If PM domains are taken into
> account, it gets even more complicated.

Yes, a minimal description would be good, along with a pointer to the 
Documentation/power files.

> > It won't be moot if you add the sentences I recommend above.  You could
> > add an additional sentence: "Either way, the @freeze() and
> > @freeze_noirq() callbacks (both the subsystem's and the driver's)  
> > should always avoid changing the device's state."
> 
> That sounds good.

Actually I meant to write "avoid changing the device's power state".

Alan Stern

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