Re: [Ksummit-discuss] [TECH TOPIC] PM dependencies

[Mark Brown <broonie@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 1547 bytes --]

On Mon, May 12, 2014 at 11:16:57PM +0200, Tomasz Figa wrote:
> On 12.05.2014 22:31, Mark Brown wrote:

> > It also solves the system suspend dependencies.  Why don't the
> > runtime PM dependencies just work with reference counting?

> Runtime PM dependencies work with reference counting just fine, but
> only for topologies matching Linux driver model, e.g. devices with
> exactly one device they depend on, e.g. SPI controller and SPI devices
> on the bus driven by it. Add there an IOMMU and other various strange
> things that should be transparent to the drivers and it stops working.

There's no reason why runtime PM references have to follow the topology
- you do get a default reference count up to any parent (though we break
that sometimes, as is the case with SPI controllers being suspended even
though the devices below them are active) but there's nothing stopping
references being taken outside the topology.

> I'm still investigating this issue, so more uses cases are yet to be
> found, but I also guess this is the purpose of this thread. Anyway,
> for some reason .suspend_late() and .resume_early() callbacks exist in
> dev_pm_ops struct and I believe that at least some of the cases
> "solved" by them might be related to the issue being discussed here.

Yes, they're partly solving a particular common case for this sort of
interdependency (though I guess they do also do things like allow us to
make sure the hardware came back in a state where it won't be harmful
to the rest of the system if we start enabling things).

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 836 bytes --]