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 13:22:43 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
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 Mon, Feb 26, 2018 at 02:05:34PM +0200, Mika Westerberg wrote:
> 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.

Okay.  Well it would be trivial to whitelist those ports with
device_property_present("HotPlugSupportInD3").  In how far are
your patches identical with the patches I submitted last May?
I've started reworking them for v2 but that would be a waste of
time if you're working on this issue in parallel.

Thanks,

Lukas