linux-kernel - Re: NAK new drivers without proper power management?

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Message-Id: <200702122131.33662.rjw@sisk.pl>
Date:	Mon, 12 Feb 2007 21:31:32 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Nigel Cunningham <nigel@...el.suspend2.net>,
	Manu Abraham <abraham.manu@...il.com>,
	Willy Tarreau <w@....eu>,
	Arjan van de Ven <arjan@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, tilman@...p.cc,
	Robert Hancock <hancockr@...w.ca>
Subject: Re: NAK new drivers without proper power management?

On Monday, 12 February 2007 17:52, Pavel Machek wrote:
> Hi!
> 
> > > > > > Neither am I. I'm just asking that new drivers have power management as
> > > > > > standard.
> > > >
> > > > > What if the hardware doesn't support power management ?
> > > >
> > > > You would still want to do the cleanup and configuration that you'd do
> > > > for module load/unload.
> > > >
> > > By adding dummy functions, wouldn't that just look awkward ?
> > 
> > If all you need to do is say 'I don't need to do anything' and we have a
> > shared function that does that, all we're talking about doing is adding
> > to your struct pci_device (or whatever)
> > 
> > .resume = generic_empty_resume;
> > 
> > To me at least, that doesn't look awkward, and says cleanly and clearly
> > that you've checked things over and decided you know what's required.
> 
> Actually, I'd like it to be
> 
> .resume = generic_empty_resume; /* Explain, why your driver needs no
> 				   resume */

Okay, but we can't define an empty .resume(), because, for example, the PCI's
generic suspend/resume won't be called.

I think we can introduce a "pm_safe" flag that will indicate if the driver
handles suspend/resume correctly.  If we do it, we can flag all of the drivers
currently in the tree as "pm_safe" unless we know that they aren't.  Next,
we can convert the core to fail the suspend for any driver that is not flagged
as "pm_safe".  But I think that will take time.

In the meantime, I'd like to ask the authors of new drivers to define
error-returning .suspend() if they don't intend to define "real" .suspend()
and .resume() for now.  When we are ready with the conversion, we'll be able
to drop the error-returning .suspend()s and clear "pm_safe" for them.

Greetings,
Rafael
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