[alsa-devel] Null suspend/resume functions

Magnus Damm magnus.damm at gmail.com
Wed Nov 18 11:09:14 CET 2009

On Tue, Nov 17, 2009 at 9:59 PM, Mark Brown
<broonie at opensource.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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