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

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Date:   Mon, 26 Feb 2018 14:05:34 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Valdis Kletnieks <Valdis.Kletnieks@...edu>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Wu <peter@...ensteyn.nl>,
        Qipeng Zha <qipeng.zha@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andreas Noever <andreas.noever@...il.com>,
        Dave Airlie <airlied@...il.com>, Qi Zheng <qi.zheng@...el.com>
Subject: Re: [PATCH v1 2/2] PCI: Allow user to request power management of
 conventional and hotplug bridges

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.