On Monday, July 25, 2016 12:48:32 AM Lukas Wunner wrote: > On Thu, Jul 21, 2016 at 02:25:15AM +0200, Rafael J. Wysocki wrote: > > On Thursday, July 21, 2016 01:25:53 AM Lukas Wunner wrote: > > > On Thu, Jul 21, 2016 at 12:51:31AM +0200, Rafael J. Wysocki wrote: > > > > On Wednesday, July 20, 2016 05:23:40 PM Lukas Wunner wrote: > > > > > On Wed, Jul 20, 2016 at 02:52:42PM +0200, Rafael J. Wysocki wrote: > > > > > > On Wednesday, July 20, 2016 08:24:50 AM Lukas Wunner wrote: > > > > > > > On Wed, Jul 20, 2016 at 02:33:18AM +0200, Rafael J. Wysocki wrote: > > > > > > > > On Friday, June 17, 2016 04:07:38 PM Lukas Wunner wrote: > > > > > > > > > On Fri, Jun 17, 2016 at 02:54:56PM +0200, Rafael J. Wysocki wrote: > > > > > > > > > > On Fri, Jun 17, 2016 at 12:36 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote: > > > > > > > > > > > On Fri, Jun 17, 2016 at 08:26:52AM +0200, Marek Szyprowski wrote: > > > > > > > > > > > > From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> > > > > > > > > > > > We also have such a functional dependency for Thunderbolt on Macs: > > > > > > > > > > > On resume from system sleep, the PCIe hotplug ports may not resume > > > > > > > > > > > before the thunderbolt driver has reestablished the PCI tunnels. > > > > > > > > > > > Currently this is enforced by quirk_apple_wait_for_thunderbolt() > > > > > > > > > > > in drivers/pci/quirks.c. It would be good if we could represent > > > > > > > > > > > this dependency using something like Rafael's approach instead of > > > > > > > > > > > open coding it, however one detail in Rafael's patches is problematic: > > > > > > > > > > > > > > > > > > > > > > > New links are added by calling device_link_add() which may happen > > > > > > > > > > > > either before the consumer device is probed or when probing it, in > > > > > > > > > > > > which case the caller needs to ensure that the driver of the > > > > > > > > > > > > supplier device is present and functional and the DEVICE_LINK_PROBE_TIME > > > > > > > > > > > > flag should be passed to device_link_add() to reflect that. > > > > > > > > > > > > > > > > > > > > > > The thunderbolt driver cannot call device_link_add() before the > > > > > > > > > > > PCIe hotplug ports are bound to a driver unless we amend portdrv > > > > > > > > > > > to return -EPROBE_DEFER for Thunderbolt hotplug ports on Macs > > > > > > > > > > > if the thunderbolt driver isn't loaded. > > > > > > > > > > > > > > > > > > > > > > It would therefore be beneficial if device_link_add() can be > > > > > > > > > > > called even *after* the consumer is bound. > > > > > > > > > > > > > > > > > > > > I don't quite follow. > > > > > > > > > > > > > > > > > > > > Who's the provider and who's the consumer here? > > > > > > > > > > > > > > > > > > thunderbolt.ko is the supplier. > > > > > > > > > > > > > > > > But it binds to the children of the ports that are supposed to be its > > > > > > > > consumers? > > > > > > > > > > > > > > > > Why is that even expected to work? > > > > > > > > > > > > > > No, the consumers are aunts (or uncles) of the supplier, if you will. :-) > > > > > > > > > > > > > > The consumers are the hotplug ports (named "Downstream Bridge 1 / 2" in > > > > > > > the drawing below). The supplier is the NHI: > > > > > > > > > > > > > > (Root Port) ---- Upstream Bridge --+-- Downstream Bridge 0 ---- NHI > > > > > > > +-- Downstream Bridge 1 -- > > > > > > > +-- Downstream Bridge 2 -- > > > > > > > ... > > > > > > > > > > > > > > We're calling pci_power_up() and pci_restore_state() from > > > > > > > pci_pm_resume_noirq(). And that will fail for devices below > > > > > > > the hotplug ports if the PCI tunnels haven't been re-established > > > > > > > yet by the NHI. > > > > > > > > > > > > So the NHI is a PCIe device, right? > > > > > > > > > > > > Does the Thunderbolt driver bind to that device? > > > > > > > > > > The NHI is a PCI device but not a bridge. It has class 0x88000. > > > > > Yes, thunderbolt.ko binds to the NHI. > > > > > > > > > > And portdrv binds to the upstream bridge and downstream bridges. > > > > > Those have class 0x60400. > > > > > > > > OK, so why would there be a problem with creating links from the NHI > > > > (producer) to the ports (consumers) before binding portdrv to them? > > > > > > Because the ordering in which drivers bind isn't guaranteed. At least > > > on my machine (Debian), portdrv always binds before thunderbolt. > > > > But what drivers have to do with that really? Do you need drivers to > > know that the dependency is there? > > > > Just add likns *before* even probing for drivers (yes, you can do that) > > and the core will handle that for you. > > Forgive me for being dense: How do you suggest to add links before > probing drivers? Only way I could think of is with a PCI quirk. > > Which is what we're already doing right now (see drivers/pci/quirk.c: > quirk_apple_wait_for_thunderbolt()). And it ain't pretty. Well, maybe not, but doing it once during enumeration would be better than on every resume. Plus there is runtime PM to cover. > > > I guess I could amend portdrv to return -EPROBE_DEFER on Macs if > > > no driver is bound to the NHI. Doesn't feel pretty to me though. > > > > > > Ultimately this seems to be the same issue as with calling > > > dev_pm_domain_set() for a bound device. Perhaps device_link_add() > > > can likewise be allowed if a runtime PM ref is held for the devices > > > and the call happens under lock_system_sleep()? > > > > No, the whole synchronization scheme in the links code would have had to be > > changed for that to really work. > > > > And it really is about what is needed (at least in principle) to run your > > device. If you think you need device X with a driver to handle device Y > > correctly, then either you need it all the time, from probe to remove, or > > you just don't really need it at all. > > Real life isn't as simple as that. > > In this case, we have consumers (hotplug ports) which are doing fine > if the driver for the supplier (NHI) is not loaded. But once it loads, > the links must be in place. Hmm. What if it is not loaded and the system suspends. Will everything work as expected after the subsequent resume? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
