On Mon, Jan 30, 2017 at 08:15:40AM +0100, Rafael J. Wysocki wrote: > On Sat, Jan 28, 2017 at 11:09 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Sun, Jan 15, 2017 at 09:03:45PM +0100, Lukas Wunner wrote: > >> Currently PCIe ports are only allowed to go to D3 if the BIOS is dated > >> 2015 or newer to avoid potential issues with old chipsets. However for > >> Thunderbolt we know that even the oldest controller, Light Ridge (2010), > >> is able to suspend its ports to D3 just fine. > >> > >> We're about to add runtime PM for Thunderbolt on the Mac. Apple has > >> released two EFI security updates in 2015 which encompass all machines > >> with Thunderbolt, but the achieved power saving should be made available > >> to users even if they haven't updated their BIOS. To this end, > >> special-case Thunderbolt in pci_bridge_d3_possible(). > > > > I think this whole paragraph is unnecessary detail. I first thought > > you had some connection with a firmware security issue, but now I see > > the only point is that if you have pre-2015 firmware, you could update > > it since newer firmware is available. > > > >> This allows the Thunderbolt controller to power down but the root port > >> to which the Thunderbolt controller is attached remains in D0 unless > >> the EFI update is installed. Users can pass pcie_port_pm=force on the > >> kernel command line if they cannot install the EFI update but still want > >> to benefit from the additional power saving of putting the root port > >> into D3. In practice, root ports can be suspended to D3 without issues > >> at least on 2012 Ivy Bridge machines. > > > > I'm not sure I like advertising pcie_port_pm=force. That just means a > > few leet folks will use this parameter and run in a subtly different > > configuration than everybody else, and possibly trip over subtly > > different issues. The audience (users who read kernel change logs and > > are willing to use special boot parameters, but who can't install an > > EFI update) seems small. > > That basically is for somebody who has a product and knows that the > feature works there, but doesn't want or simply can't patch the kernel > (which is shipped by a distro or similar). Yes, OK. This isn't adding a new parameter, and I'm OK with the actual change here, so Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
