On Fri, Jun 17, 2016 at 12:36 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote: > Hi Marek, > > On Fri, Jun 17, 2016 at 08:26:52AM +0200, Marek Szyprowski wrote: >> From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> >> >> Currently, there is a problem with handling cases where functional >> dependencies between devices are involved. >> >> What I mean by a "functional dependency" is when the driver of device >> B needs both device A and its driver to be present and functional to >> be able to work. This implies that the driver of A needs to be >> working for B to be probed successfully and it cannot be unbound from >> the device before the B's driver. This also has certain consequences >> for power management of these devices (suspend/resume and runtime PM >> ordering). >> >> Add support for representing those functional dependencies between >> devices to allow the driver core to track them and act on them in >> certain cases where they matter. > > Rafael has indicated that he intends to respin this series: > https://lkml.org/lkml/2016/6/8/1061 That's OK. > 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? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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