linux-kernel - Re: [PATCH 1/2] vga_switcheroo: add power support for windows 10 machines.

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Message-ID: <CAJZ5v0igUCP8-uH+VUb5KmUeZv5khtMJRjUh-z=orHOgRrcmiw@mail.gmail.com>
Date:	Mon, 14 Mar 2016 13:50:41 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Dave Airlie <airlied@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] vga_switcheroo: add power support for windows 10 machines.

On Mon, Mar 14, 2016 at 11:23 AM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> On Mon, Mar 14, 2016 at 07:47:39PM +1000, Dave Airlie wrote:
>> >
>> >> -     if (pcie_port_runtime_suspend_allowed(dev))
>> >> +     if (pcie_port_runtime_suspend_allowed(dev)) {
>> >> +             pm_runtime_allow(&dev->dev);
>> >
>> > PCI drivers typically have left this decision up to the userspace. I'm
>> > wondering whether it is good idea to deviate from that here? Of course
>> > this allows immediate power savings but could potentially cause problems
>> > as well.
>> >
>>
>> No distro has ever shipped userspace to do this, I really think this
>> is a bad design.
>> We have wasted countless watts of power on this stupid idea that people will
>> run powertop, only a few people in the world run powertop, lots of
>> people use Linux.
>
> That is a fair point.
>
> I do not have anything against calling pm_runtime_allow() here. In fact
> we already do the same in Intel LPSS drivers. I just wanted to bring
> that up.
>
> Rafael, what do you think?

We can do that to start with.  If there are no problems in the field
with it, I don't see any problems in principle.

> If we anyway are going to add cut-off date to enable runtime PM we
> should expect that the hardware is also capable of doing so (and if not
> we can always blacklist the exceptions).

Sounds reasonable.

>> The kernel should power stuff down not wait for the user to run powertop,
>> At least for the GPU it's in the area of 8W of power, and I've got the
>> GPU drivers doing this themselves,
>>
>> I could have the GPU driver call runtime allow for it's host bridge I suppose,
>> if we insist on the userspace cares, but I'd prefer not doing so.
>>
>> > I think we need to add corresponding call to pm_runtime_forbid() in
>> > pcie_portdrv_remove().
>>
>> Yes most likely.
>
> BTW, I can add both calls to the next version of PCIe runtime PM patches
> if you are OK with that, and all agree this is a good idea.

That would be fine by me.

Thanks,
Rafael