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

[Mika Westerberg]

On Mon, Mar 14, 2016 at 01:50:41PM +0100, Rafael J. Wysocki wrote:
> On Mon, Mar 14, 2016 at 11:23 AM, Mika Westerberg
> <mika.westerberg@xxxxxxxxxxxxxxx> 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.

OK thanks.

I'll do these changes to the next version of the patch series then.