On 31 May 2018 at 11:14, Viresh Kumar [off-list ref] wrote:

On 29-05-18, 12:04, Ulf Hansson wrote:

quoted

Changes in v2:
      - Addressed comments from Geert around DT doc.
      - Addressed comments from Jon around clarification of how to use this
      and changes to returned error codes.
      - Fixed build error in case CONFIG_PM was unset.

There are devices that are partitioned across multiple PM domains. Currently
these can't be supported well by the available PM infrastructures we have in
the kernel. This series is an attempt to address this.

The interesting parts happens from patch 5 an onwards, including a minor DT
update to the existing power-domain bindings, the 4 earlier are just trivial
clean-ups of some related code in genpd, which I happened to stumble over.

Some additional background:

One existing case where devices are partitioned across multiple PM domains, is
the Nvida Tegra 124/210 X-USB subsystem. A while ago Jon Hunter (Nvidia) sent a
series, trying to address these issues, however this is a new approach, while
it re-uses the same concepts from DT point of view.

The Tegra 124/210 X-USB subsystem contains of a host controller and a device
controller. Each controller have its own independent PM domain, but are being
partitioned across another shared PM domain for the USB super-speed logic.

Currently to make the drivers work, either the related PM domains needs to stay
powered on always or the PM domain topology needs to be in-correctly modelled
through sub-domains. In both cases PM domains may be powered on while they
don't need to be, so in the end this means - wasting power -.

As stated above, this series intends to address these problem from a PM
infrastructure point of view. More details are available in each changelog.

It should be noted that this series has been tested on HW, however only by using
a home-cooked test PM domain driver for genpd and together with a test driver.
This allowed me to play with PM domain (genpd), runtime PM and device links.

Any further deployment for real use cases are greatly appreciated. I am happy to
to help, if needed!

Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>

Thanks!

Kind regards
Uffe