On Sat, Mar 31, 2018 at 11:56 AM, Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> wrote: > On Sat, Mar 31, 2018 at 11:30:44AM +0200, Rafael J. Wysocki wrote: >> > The whole point here is that those are *not* hotplug slots just regular >> > downstream ports. >> >> I'm not sure what scenario exactly you are referring to to be honest. >> >> Something related to Thunderbolt I suppose? > > Here is an example that hopefully clarifies. This example is from a > system using Thunderbolt in "native" mode but I think it is not specific > to Thunderbolt. The idea is that when you don't have anything connected > to Thunderbolt ports you have following PCI topology: > > 00:1b.0 -- > > So a root port that is hotplug capable and handled by pciehp. > > Next when you plug in a Thunderbolt enpdoint, you get native PCIe > hotplug event and after it is handled the topology looks like: > > 00:1b.0 --- 01:00.0 --+- 02:00.0 -- > +- 02:01.0 (hotplug) -- > \- 02:02.0 -- > > In other words there is a PCIe switch with one hotplug port (02:01.0) > that is again handled by pciehp (this is used to daisy chain further > devices). However, downstream ports 02:00.0 and 02:02.0 are not marked > as hotplug capable so pciehp is not controlling them. > > To bring in xHCI and/or Thunderbolt host controller we get ACPI Notify() > to the root port 00:1b.0 which should result following topology after > handled by acpiphp: > > 00:1b.0 --- 01:00.0 --+- 02:00.0 -- Thunderbolt host controller > +- 02:01.0 (hotplug) -- > \- 02:02.0 -- xHCI host controller > > In other words ACPI Notify() is used to populate devices connected to > non-hotplug downstream ports. It is also used to "hot-unplug" them in > the same way (for example if you only connect standard USB-C device to > the port the Thunderbolt host controller is hot-unplugged using this > mechanism). > > Rest of the devices in the chain are hotplugged using standard native > PCIe hotplug so pciehp will be controlling then. OK, thanks! I thought it would be something like this. :-) So the mechanism is not TBT-specific in principle, but I don't think that it is used in practice anywhere outside of Thunderbolt. I also think that it would be good to put the above example somewhere like a git commit changelog or even a comment in the code, so people in the future don't have to wonder what this is all about. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
