linux-kernel - Re: Null suspend/resume functions

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Date:	Tue, 17 Nov 2009 23:14:04 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Magnus Damm <magnus.damm@...il.com>,
	Kuninori Morimoto <morimoto.kuninori@...esas.com>,
	alsa-devel@...a-project.org, linux-pm@...ts.linux-foundation.org,
	Magnus Damm <damm@...nsource.se>, linux-kernel@...r.kernel.org
Subject: Re: Null suspend/resume functions

On Tuesday 17 November 2009, Mark Brown wrote:
> On Tue, Nov 17, 2009 at 09:46:35PM +0900, Magnus Damm wrote:
> 
> > On SuperH we have Runtime PM enabled on a few platforms together with
> > a few updated drivers. The latest driver to become more power aware is
> > this FSI driver.
> 
> I understand exactly what the runtime PM stuff and the driver are doing
> here, the issue is the mandatory suspend and resume functions.
> 
> > At this point the SuperH specific platform bus code requires the
> > callbacks ->runtime_suspend() and ->runtime_resume() to be present. It
> > may be a good idea to allow them to be NULL in the future or maybe
> > having some shared functions, but before starting to break out stuff
> > I'd like to see how other Runtime PM implementations deal with this.
> > So unless people object I prefer to keep it as-is for now.
> 
> What is the reason for requiring that the driver provide stub functions?
> For me the issue is that if it's mandatory for the driver to provide the
> functions then having stub functions in there makes the driver look like
> it is abusing the API by not implementing mandatory functionality.

In fact, it's not mandatory for bus types, not for drivers.  IMO bus types
really have to know how to suspend a device and how to resume it,
otherwise the core framework won't be useful anyway.  What the bus type does
about drivers not implementing ->runtime_suspend() or ->runtime_resume(), it's
up to the bus type.  That's even documented IIRC.

Thanks,
Rafael
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