The Tegra124/210 XUSB subsystem (that consists of both host and device
controllers) is partitioned across 3 PM domains which are:
- XUSBA: Superspeed logic (for USB 3.0)
- XUSBB: Device controller
- XUSBC: Host controller

These power domains are not nested and can be powered-up and down
independently of one another. In practice different scenarios require
different combinations of the power domains, for example:
- Superspeed host: XUSBA and XUSBC
- Superspeed device: XUSBA and XUSBB

Although it could be possible to logically nest both the XUSBB and XUSBC
domains under the XUSBA, superspeed may not always be used/required and
so this would keep it on unnecessarily.

Given that Tegra uses device-tree for describing the hardware, it would
be ideal that the device-tree 'power-domains' property for generic PM
domains could be extended to allow more than one PM domain to be
specified. For example, define the following the Tegra210 xHCI device ...

        usb@70090000 {
                compatible = "nvidia,tegra210-xusb";
                power-domains = <&pd_xusbhost>, <&pd_xusbss>;

This RFC extends the generic PM domain framework to allow a device to
define more than one PM domain in the device-tree 'power-domains'

Jon Hunter (3):
  PM / Domains: Add helper functions for finding and attaching PM
  PM / Domains: Add support for devices with multiple domains
  dt-bindings: Add support for devices with multiple PM domains

 .../devicetree/bindings/power/power_domain.txt     |   5 +-
 drivers/base/power/domain.c                        | 205 +++++++++++++++------
 2 files changed, 155 insertions(+), 55 deletions(-)


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