linux-kernel - Re: Null suspend/resume functions

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Message-ID: <aec7e5c30911180209x1981978es80db2dadf7dd8ef4@mail.gmail.com>
Date:	Wed, 18 Nov 2009 19:09:14 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	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 Tue, Nov 17, 2009 at 9:59 PM, Mark Brown
<broonie@...nsource.wolfsonmicro.com> 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.

Cool, but don't you think it makes sense to see how other
architectures will deal with this first?

>> 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.

I see your point, but there is another side to it as well. Having the
stubs there is a way of showing that these functions may be called as
part of the Runtime PM management. Not having them would confuse
people even more IMO.

> Given that the arch is now dealing with clocking and power for the
> device using the runtime PM system it seems fairly clear that there are
> going to be drivers like this one that can at least skip the suspend
> part and may not need to do anything at resume time either.

Right. We just need to figure out what the arch-independent solution
would be, and we're unfortunately not there yet.

I can spend some time on updating the drivers and removing the
nop-stubs if you'd like, but I'd rather not since I suspect that I'll
have to update things again when we get Runtime PM for ARM or other
non-sh architectures.

Let me know what you think!

/ magnus
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