Re: [PATCH v1 2/2] PCI: Allow user to request power management of conventional and hotplug bridges

[Mika Westerberg]

On Thu, Feb 22, 2018 at 02:18:34PM +0100, Lukas Wunner wrote:
> We do need runtime PM on hotplug ports to power off Thunderbolt
> controllers when nothing is plugged in.  That saves 1.5 W, so a
> noticeable amount of power.  I was going to respin the series one
> of these days, I think the best I can do is continue to forbid
> runtime PM on hotplug ports by default, but whitelist it for
> Thunderbolt and allow manually enabling it on other platforms via
> the command line.  That way, vendors are put in a position to
> validate their platforms for runtime PM of hotplug ports, and
> perhaps someday we can enable it for all platforms by default,
> but with a BIOS cut-off date.

AFAIK Windows started to enable runtime PM (RTD3) for native PCIe
hotplug ports with the latest release (I guess it's the RS3 release) but
only when there is a special ACPI _DSD property ("HotPlugSupportInD3")
associated with the root port. I think we can take advantage of that in
Linux as well and I already have a patch series to enable runtime PM for
such ports but I haven't been able to test it properly yet.